The Effectiveness of Resistance Exercises Performed on Unstable
The Effectiveness of Resistance Exercises Performed on Unstable Equipment
Jeffrey M. Willardson, MS
Arizona State University, Tempe, Arizona
ABSTRACT
The performance of resistance exercises on unstable equipment has increased in popularity, despite the lack of research supporting their effectiveness. Resistance exercise performed on unstable equipment may not be effective in developing the type of balance, proprioception, and core stability required for successful sports performance. Free weight exercises performed while standing on a stable surface have been proven most effective for enhancing sports related skills.
Key Words: skill transfer, balance, proprioception, core stability
One of the latest trends among fitness professionals is to instruct clients to perform resistance exercises on unstable equipment. Many companies have contributed to this trend by marketing various types of unstable equipment such as stability balls, foam rollers, wobble boards, and variations of such equipment. Some fitness professionals claim exercises performed on unstable equipment are effective for enhancing sports performance (5, 6, 8, 10, 16, 20, 21). However, these authors have not cited research that supports their claims. Additionally, there is little information in the texts and position stands endorsed by the National Strength and Conditioning Association and the American College of Sports Medicine that validates the effectiveness of these exercises (2, 3, 14).
The majority of studies demonstrating the effectiveness of resistance exercises for enhancing sports performance have used exercises performed on a stable surface (12, 15, 19, 22, 23). A stable surface in this context refers to a solid, level surface that does not move. The purpose of this article will be to question the effectiveness of resistance exercises performed on unstable equipment for enhancing sports performance. Research related to the topic as well as claims made by proponents of these exercises will be discussed and evaluated. This article will be divided into 3 sections: (a) specificity in resistance training, (b) core stabilization, and (c) resistance training for sports.
Specificity in Resistance Training
The exercises prescribed within a resistance-training program should be dependent on the specific physiological and biomechanical demands of a sport or position within a sport (1–3, 11, 12, 14, 18, 19, 22, 26). The design of a resistance-training program can be structured to promote different outcomes such as muscular power, muscular strength, muscular hypertrophy, localized muscular endurance, movement efficiency, movement velocity, proprioception, balance, and core stability (2, 3, 7, 14, 26). The specificity of a resistance-training program is determined by the extent to which training exercises transfer to sports performance.
Authors have claimed that resistance exercises performed on unstable equipment are specific to sports skills because of the balance, proprioception, and core stability required to perform these exercises successfully (5, 6, 8, 10, 16, 20, 21). Although resistance exercises performed on unstable equipment can be challenging, research has not demonstrated that the type of balance, proprioception, and core stability developed through these exercises will transfer to any sports skill. Therefore, performing resistance exercises on unstable equipment will make an individual proficient at performing resistance exercises on unstable equipment but may not enhance the performance of sports skills.
For example, having a gymnast balance on a wobble board may not improve balance-beam performance, because balance is skill specific. Likewise, having a baseball pitcher perform medicine-ball throws while standing on a foam roller may not improve proprioception when throwing from a mound, because proprioception is skill specific. Similarly, having a football running back perform squats while standing on stability disks may not improve core stability when running through a defensive line, because stability is skill specific. The optimal method to promote increases in balance, proprioception, and core stability for any given sports skill is to practice the skill itself on the same surface on which the skill is performed during competition (1, 18, 24).
Research has shown little transfer between different balance skills. Drowatzky and Zuccato (9) analyzed the relationship between 6 measures of static and dynamic balance. The static balance measures included a stork stand, diver's stand, and stick test. The dynamic balance measures included a sideward leap, Bass stepping-stone test, and balance-beam test. Pearson product-moment correlation coefficients were computed between each of the balance tests. Out of the 15 correlations computed, only the correlation between the sideward leap and Bass stepping-stone test was found to be significant, but this was low and possessed little predictive value (r = 0.3083). The authors concluded that each of the balance tests measured a different type of balance. These results suggest very little transfer between skills that require static balance and skills that require dynamic balance. Resistance exercises performed on unstable equipment, which require a high level of static balance, may not transfer to sports skills, which require a high level of dynamic balance.
Specificity is an important factor to consider when exercises are prescribed for a resistance-training program (2,3,14,26). Sports skills are performed under a variety of conditions, which increases the difficulty in deciding upon appropriate exercises. Although 100% specificity is impossible to achieve, exercises should be chosen that most closely mimic the demands of a sport. A review by Sale and MacDougall (19) emphasized that specificity of resistance training is increased when factors such as movement pattern, muscle action, muscular force output, and movement velocity are considered.
When practicing sports-related skills, the use of a stability ball, foam roller, or wobble board may actually reduce specificity. For example, there are no sports that require an individual to squat while standing on any surface that resembles a stability disk, foam roller, or wobble board. The majority of sports are played on a solid, level surface that does not move. Exceptions may include ice hockey, snow skiing, beach volleyball, and swimming. However, performing resistance exercises on unstable equipment has not been shown to enhance any skill related to these sports.
As an individual masters a given movement pattern, a specific neuromuscular pattern is created that is unique to that movement alone. This specific neuromuscular pattern is called an engram (24). Movement patterns are generally learned at a low velocity and then practiced until they can be performed at a high velocity (1, 18). Two problems may arise when exercises are performed on unstable equipment with the intent to mimic the skills required by a given sport.
First, an individual may be mastering two separate skills, one that includes the unstable equipment and another that is required by the sport. Even though the movement patterns may look similar, the underlying neuromuscular recruitment patterns and proprioceptive feedback may be completely different (1, 9, 18, 24, 26). For example, throwing a baseball while standing on a stable surface might be different from throwing a baseball while standing on a wobble board. A potential disadvantage in this case is that practice time that could be spent mastering the actual skill is wasted with time spent mastering a different unstable skill. Second, introducing anything foreign to a skill such as a stability ball, foam roller, or wobble board might confuse the original neuromuscular recruitment pattern, creating a negative transfer and a resulting decrement in performance (1, 18, 24).
There is no guarantee that any resistance exercise will transfer to sports performance, regardless of whether the exercise is performed on a stable or an unstable surface. However, free-weight exercises performed while standing on a stable surface may result in the highest degree of transfer. Free-weight exercises performed in this manner require the type of balance, proprioception, and core stability that more closely mimics the demands of sports-related skills (2, 3, 11, 14, 19, 22, 26). Examples of a few stable free-weight exercises proven to be effective include the squat, dead lift, power clean, standing shoulder press, and push press (3, 11, 12, 22, 23, 26).
Although different muscle actions (i.e., concentric, eccentric, isometric) might be emphasized on a stability ball, muscular force output is significantly reduced (4, 17). Muscular force output has been shown to be a key factor that determines muscular overload and subsequent strength gains (2, 3, 14). To maximize strength increases, the target musculature must be loaded with an amount of resistance that allows for sufficient recruitment of muscle fibers. When resistance exercises are performed on unstable equipment, muscular force output is significantly reduced, with a concomitant reduction in muscle fiber recruitment and muscular overload (4, 17).
Behm et al. (4) examined isometric force output and muscle activation of agonist and antagonist muscle groups with subjects seated on a stable versus an unstable surface. Eight subjects performed unilateral leg extension (LE) and plantar flexion (PF) muscle actions while seated on a bench or stability ball. Subjects were either resistance trained or had previous resistance-training experience. For the LE, the agonist/antagonist muscle groups were considered to be the quadriceps/hamstrings. For the PF, the agonist/antagonist muscle groups were considered to be the soleus/tibialis anterior.
For the agonist muscle groups, isometric force output was reported to be 70.5% (LE) and 20.2% (PF) less when muscle actions were performed on a stability ball. Muscle activation followed the same pattern, with 44.3% (LE) and 2.9% (PF) less activation when muscle actions were performed on a stability ball. In contrast, for the antagonistic muscle groups, muscle activation was 40.2% (LE) and 30.7% (PF) greater when muscle actions were performed on a stability ball.
Although Behm et al. (4) demonstrated greater activity in the antagonist or “stabilizer” muscle groups when muscle actions were performed on a stability ball, this does not indicate that these exercises are more effective for enhancing sports performance. First, this was a cross-sectional study, and subjects were not tested for improved performance in any sports-related skill. Second, isometric force output of the agonist muscle groups was reduced, which has been shown to limit gains in strength and power (2, 3, 14). Third, the stability requirements of stability ball exercises might be different from the stability requirements of sports skills (1,9,18,24).
Core Stabilization
Recently, much attention has been given to the importance of core stabilization. The term “core” is used to describe collectively a group of muscles that stabilize the lumbar spine and pelvis. Some of these muscles include the rectus abdominis, transversus abdominis, internal and external oblique, erector spinae, and multifidi (13). Hodges and Richardson (13) demonstrated that when subjects performed a unilateral shoulder movement, the transversus abdominis was the first of the trunk muscles to become active, and this activation occurred prior to the onset of actual limb movement. This study suggests that for the throwing athlete, core stability would be important as force is transferred from the ground, up through the lower extremities, across the trunk, and out to the throwing arm.
Some authors have claimed that when resistance exercises are performed on a stable surface, muscular stabilization is reduced, thus creating the need for resistance exercises performed on unstable equipment (5, 6, 8, 10, 16, 20, 21). However, improvements in stability consequent to performing resistance exercises on unstable equipment may not transfer to improvements in sports performance. According to Yessis (25), “Isolated core strengthening, when not accompanied by appropriate motor skills training, does not automatically enhance core stability, or the ability to maintain or adjust posture during execution of an exercise or sports skill” (p. 27). This suggests that in order to increase core stabilization, core-strengthening exercises must be accompanied by sports skill practice.
Unstable resistance exercises might be ineffective for core strengthening for 2 reasons. First, there is difficulty in applying a progressive overload. During the early phases of training, performing only unstable resistance exercises may provide a sufficient overload to the core musculature. However, strength levels may ultimately increase to the point that unstable equipment can no longer be effectively and safely used. This is because a progressive overload can only be achieved by either increasing the resistance or decreasing the stability, both of which can increase the risk for injury.
For example, a typical progression for a shoulder press might be performing the exercise while seated on a stability ball with 2 feet on the floor, then with 1 foot on the floor, and finally while standing on a wobble board (6). When performing exercises such as the squat, dead lift, power clean, standing shoulder press, and push press, the inclusion of unstable equipment has not been shown to be safe or effective.
Second, the use of resistance exercises performed on unstable equipment makes planning a periodized program difficult because a 1 repetition maximum (1RM) cannot safely be determined and strength gains are difficult to measure. Some may argue that these exercises can be performed on “light” days to maintain strength. However, the amount of resistance that can safely be used while training on unstable equipment may not be sufficient to maintain strength gains (4, 17). When considering exercises to increase core strength, free-weight exercises performed while standing on a stable surface may provide the best combination of muscular overload and neuromuscular specificity to sports skills (2, 3, 11, 12, 14, 15, 22, 23, 25, 26).
Although any resistance exercise performed incorrectly can result in injury, the risks involved when performing stable free-weight exercises are minimal. Zemper (27) conducted a 4-year study of weight-room injuries in a national sample of college football teams. The results indicated that the rate of time-loss injuries during weight room activities was less than 1% of the total football injuries reported. The teams sampled performed mostly free-weight exercises while standing on a stable surface.
According to Yessis (25), “Performing free weight exercises on a stable surface is much safer than performing exercises on an unstable surface, where exercisers must give equal or greater attention to maintaining balance instead of exercise execution” (p. 27). Free-weight exercises such as the squat, dead lift, power clean, standing shoulder press, and push press have been shown to load safely the core musculature (27). When these free-weight exercises are performed while standing on a stable surface, many of the core muscles function as stabilizers, either isometrically or dynamically with small concentric or eccentric muscle actions (3,22,25,26). The increased core strength can then be applied to the practice of sport skills to increase core stability and decrease the risk for injuries.
Resistance Training for Sports
Resistance training is an important priority for most sports-training programs. Muscular adaptations are specific to the repetition range and velocity being trained (2, 3, 7, 19, 22). Different sports require different approaches in the way that the muscles are trained. For example, sports such as American football require short duration maximal strength, which necessitates training with relatively heavy loads. Other sports such as cycling require long duration muscular endurance, which necessitates training with relatively light loads (2, 3, 7).
Most sports require individuals to develop strength at both low and high movement velocities, which has been shown to maximize muscular power (12, 23). To develop low-velocity strength, exercises are performed in the same manner as described previously for maximal strength. Because the resistance is near maximal, movement velocity is unintentionally slow. In contrast, to develop high-velocity strength, resistance exercises are performed with submaximal resistance (30–60% of 1RM), and velocity of movement is intentionally fast (2, 3, 19, 22, 26).
Research has repeatedly demonstrated the effectiveness of stable free-weight exercises for enhancing sports-related skills (11, 12, 15, 19, 22, 23). In contrast, not a single study has demonstrated the effectiveness of resistance exercises performed on unstable equipment. Garhammer (11) advocated stable free-weight exercises based on the “multi-joint, multi-muscle group nature of total body free weight exercises, and the resulting neuromuscular specificity and transferability to sport activities” (p. 25). The effectiveness of stable free-weight exercises for enhancing sports skills has been thoroughly reviewed elsewhere (11,14,19,22). However, this article will discuss the key findings from a few relevant studies.
Stone et al. (23) demonstrated that stable free-weight exercises were most effective for increasing vertical jump. Some of the exercises included the push press, squat (full and quarter), and clean-pull. The authors concluded that the stable free-weight exercises exhibited a high degree of mechanical specificity to the vertical jump.
Newton and McEvoy (15) demonstrated that stable free-weight exercises were most effective for increasing throwing velocity. Subjects performed stable free-weight exercises such as the barbell pullover and bench press with a 6–10RM load. The authors concluded that the stable free-weight exercises increased the strength of the muscles involved in the throwing motion, which transferred to greater throwing velocity.
Harris et al. (12) demonstrated that improvement in several sports-related skills was greatest when stable free-weight exercises were performed at both “slow” and “fast” movement velocities. Some of the exercises included the parallel and quarter squat, push press, mid-thigh pull, and bent-over row. Improvement was demonstrated in the following skills: the vertical jump, standing long jump, 10-yd shuttle, and 30-m sprint. The authors concluded that the combination of “slow” and “fast” movement velocities increased muscular power, which transferred to greater improvements in sport skill performance.
Conclusion
Based on the research that currently exists, the optimal approach for enhancing sports performance is to perform free-weight exercises while standing on a stable surface to increase muscular overload and the stimulus for strength gains (2, 3, 11, 12, 14, 19, 22, 23, 25, 26). The increased strength developed in the weight room can then be applied to the practice of sports skills to enhance performance. Resistance exercises performed on unstable equipment have not been proven to be safe or effective in developing the type of balance, proprioception, and core stability necessary for successful sports performance.
Because the majority of sports are played on a stable surface, exercises designed to increase balance, proprioception, and core stability should be performed on a stable surface. Exceptions may include sports such as ice hockey, snow skiing, beach volleyball, and swimming. However, exercises designed to increase balance, proprioception, and core stability for these sports might best be performed on ice, snow, sand, or in the water, respectively (1, 18, 24).
Although there is no guarantee that any resistance exercise will transfer to sports performance, free-weight exercises performed while standing on a stable surface may result in the highest degree of transfer. Exercises such as the squat, dead lift, power clean, standing shoulder press, and push press have been demonstrated to be effective for enhancing performance in several sports-related skills (2, 3, 11, 12, 14, 19, 22, 23, 25, 26). There is little information in the texts and position stands endorsed by the National Strength and Conditioning Association and the American College of Sports Medicine that validates the effectiveness of resistance exercises performed on unstable equipment (2, 3, 14). No study has demonstrated improvement in any sports skill consequent to performing these exercises.
With the lack of research currently available, fitness professionals must be cautious in prescribing resistance exercises performed on unstable equipment. The majority of claims made by proponents of these exercises are currently undocumented (5, 6, 8, 10, 16, 20, 21). Hopefully, this paper will stimulate more research that examines the effectiveness of resistance exercises performed on unstable equipment for enhancing sports performance.
Jeffrey M. Willardson, MS
Arizona State University, Tempe, Arizona
ABSTRACT
The performance of resistance exercises on unstable equipment has increased in popularity, despite the lack of research supporting their effectiveness. Resistance exercise performed on unstable equipment may not be effective in developing the type of balance, proprioception, and core stability required for successful sports performance. Free weight exercises performed while standing on a stable surface have been proven most effective for enhancing sports related skills.
Key Words: skill transfer, balance, proprioception, core stability
One of the latest trends among fitness professionals is to instruct clients to perform resistance exercises on unstable equipment. Many companies have contributed to this trend by marketing various types of unstable equipment such as stability balls, foam rollers, wobble boards, and variations of such equipment. Some fitness professionals claim exercises performed on unstable equipment are effective for enhancing sports performance (5, 6, 8, 10, 16, 20, 21). However, these authors have not cited research that supports their claims. Additionally, there is little information in the texts and position stands endorsed by the National Strength and Conditioning Association and the American College of Sports Medicine that validates the effectiveness of these exercises (2, 3, 14).
The majority of studies demonstrating the effectiveness of resistance exercises for enhancing sports performance have used exercises performed on a stable surface (12, 15, 19, 22, 23). A stable surface in this context refers to a solid, level surface that does not move. The purpose of this article will be to question the effectiveness of resistance exercises performed on unstable equipment for enhancing sports performance. Research related to the topic as well as claims made by proponents of these exercises will be discussed and evaluated. This article will be divided into 3 sections: (a) specificity in resistance training, (b) core stabilization, and (c) resistance training for sports.
Specificity in Resistance Training
The exercises prescribed within a resistance-training program should be dependent on the specific physiological and biomechanical demands of a sport or position within a sport (1–3, 11, 12, 14, 18, 19, 22, 26). The design of a resistance-training program can be structured to promote different outcomes such as muscular power, muscular strength, muscular hypertrophy, localized muscular endurance, movement efficiency, movement velocity, proprioception, balance, and core stability (2, 3, 7, 14, 26). The specificity of a resistance-training program is determined by the extent to which training exercises transfer to sports performance.
Authors have claimed that resistance exercises performed on unstable equipment are specific to sports skills because of the balance, proprioception, and core stability required to perform these exercises successfully (5, 6, 8, 10, 16, 20, 21). Although resistance exercises performed on unstable equipment can be challenging, research has not demonstrated that the type of balance, proprioception, and core stability developed through these exercises will transfer to any sports skill. Therefore, performing resistance exercises on unstable equipment will make an individual proficient at performing resistance exercises on unstable equipment but may not enhance the performance of sports skills.
For example, having a gymnast balance on a wobble board may not improve balance-beam performance, because balance is skill specific. Likewise, having a baseball pitcher perform medicine-ball throws while standing on a foam roller may not improve proprioception when throwing from a mound, because proprioception is skill specific. Similarly, having a football running back perform squats while standing on stability disks may not improve core stability when running through a defensive line, because stability is skill specific. The optimal method to promote increases in balance, proprioception, and core stability for any given sports skill is to practice the skill itself on the same surface on which the skill is performed during competition (1, 18, 24).
Research has shown little transfer between different balance skills. Drowatzky and Zuccato (9) analyzed the relationship between 6 measures of static and dynamic balance. The static balance measures included a stork stand, diver's stand, and stick test. The dynamic balance measures included a sideward leap, Bass stepping-stone test, and balance-beam test. Pearson product-moment correlation coefficients were computed between each of the balance tests. Out of the 15 correlations computed, only the correlation between the sideward leap and Bass stepping-stone test was found to be significant, but this was low and possessed little predictive value (r = 0.3083). The authors concluded that each of the balance tests measured a different type of balance. These results suggest very little transfer between skills that require static balance and skills that require dynamic balance. Resistance exercises performed on unstable equipment, which require a high level of static balance, may not transfer to sports skills, which require a high level of dynamic balance.
Specificity is an important factor to consider when exercises are prescribed for a resistance-training program (2,3,14,26). Sports skills are performed under a variety of conditions, which increases the difficulty in deciding upon appropriate exercises. Although 100% specificity is impossible to achieve, exercises should be chosen that most closely mimic the demands of a sport. A review by Sale and MacDougall (19) emphasized that specificity of resistance training is increased when factors such as movement pattern, muscle action, muscular force output, and movement velocity are considered.
When practicing sports-related skills, the use of a stability ball, foam roller, or wobble board may actually reduce specificity. For example, there are no sports that require an individual to squat while standing on any surface that resembles a stability disk, foam roller, or wobble board. The majority of sports are played on a solid, level surface that does not move. Exceptions may include ice hockey, snow skiing, beach volleyball, and swimming. However, performing resistance exercises on unstable equipment has not been shown to enhance any skill related to these sports.
As an individual masters a given movement pattern, a specific neuromuscular pattern is created that is unique to that movement alone. This specific neuromuscular pattern is called an engram (24). Movement patterns are generally learned at a low velocity and then practiced until they can be performed at a high velocity (1, 18). Two problems may arise when exercises are performed on unstable equipment with the intent to mimic the skills required by a given sport.
First, an individual may be mastering two separate skills, one that includes the unstable equipment and another that is required by the sport. Even though the movement patterns may look similar, the underlying neuromuscular recruitment patterns and proprioceptive feedback may be completely different (1, 9, 18, 24, 26). For example, throwing a baseball while standing on a stable surface might be different from throwing a baseball while standing on a wobble board. A potential disadvantage in this case is that practice time that could be spent mastering the actual skill is wasted with time spent mastering a different unstable skill. Second, introducing anything foreign to a skill such as a stability ball, foam roller, or wobble board might confuse the original neuromuscular recruitment pattern, creating a negative transfer and a resulting decrement in performance (1, 18, 24).
There is no guarantee that any resistance exercise will transfer to sports performance, regardless of whether the exercise is performed on a stable or an unstable surface. However, free-weight exercises performed while standing on a stable surface may result in the highest degree of transfer. Free-weight exercises performed in this manner require the type of balance, proprioception, and core stability that more closely mimics the demands of sports-related skills (2, 3, 11, 14, 19, 22, 26). Examples of a few stable free-weight exercises proven to be effective include the squat, dead lift, power clean, standing shoulder press, and push press (3, 11, 12, 22, 23, 26).
Although different muscle actions (i.e., concentric, eccentric, isometric) might be emphasized on a stability ball, muscular force output is significantly reduced (4, 17). Muscular force output has been shown to be a key factor that determines muscular overload and subsequent strength gains (2, 3, 14). To maximize strength increases, the target musculature must be loaded with an amount of resistance that allows for sufficient recruitment of muscle fibers. When resistance exercises are performed on unstable equipment, muscular force output is significantly reduced, with a concomitant reduction in muscle fiber recruitment and muscular overload (4, 17).
Behm et al. (4) examined isometric force output and muscle activation of agonist and antagonist muscle groups with subjects seated on a stable versus an unstable surface. Eight subjects performed unilateral leg extension (LE) and plantar flexion (PF) muscle actions while seated on a bench or stability ball. Subjects were either resistance trained or had previous resistance-training experience. For the LE, the agonist/antagonist muscle groups were considered to be the quadriceps/hamstrings. For the PF, the agonist/antagonist muscle groups were considered to be the soleus/tibialis anterior.
For the agonist muscle groups, isometric force output was reported to be 70.5% (LE) and 20.2% (PF) less when muscle actions were performed on a stability ball. Muscle activation followed the same pattern, with 44.3% (LE) and 2.9% (PF) less activation when muscle actions were performed on a stability ball. In contrast, for the antagonistic muscle groups, muscle activation was 40.2% (LE) and 30.7% (PF) greater when muscle actions were performed on a stability ball.
Although Behm et al. (4) demonstrated greater activity in the antagonist or “stabilizer” muscle groups when muscle actions were performed on a stability ball, this does not indicate that these exercises are more effective for enhancing sports performance. First, this was a cross-sectional study, and subjects were not tested for improved performance in any sports-related skill. Second, isometric force output of the agonist muscle groups was reduced, which has been shown to limit gains in strength and power (2, 3, 14). Third, the stability requirements of stability ball exercises might be different from the stability requirements of sports skills (1,9,18,24).
Core Stabilization
Recently, much attention has been given to the importance of core stabilization. The term “core” is used to describe collectively a group of muscles that stabilize the lumbar spine and pelvis. Some of these muscles include the rectus abdominis, transversus abdominis, internal and external oblique, erector spinae, and multifidi (13). Hodges and Richardson (13) demonstrated that when subjects performed a unilateral shoulder movement, the transversus abdominis was the first of the trunk muscles to become active, and this activation occurred prior to the onset of actual limb movement. This study suggests that for the throwing athlete, core stability would be important as force is transferred from the ground, up through the lower extremities, across the trunk, and out to the throwing arm.
Some authors have claimed that when resistance exercises are performed on a stable surface, muscular stabilization is reduced, thus creating the need for resistance exercises performed on unstable equipment (5, 6, 8, 10, 16, 20, 21). However, improvements in stability consequent to performing resistance exercises on unstable equipment may not transfer to improvements in sports performance. According to Yessis (25), “Isolated core strengthening, when not accompanied by appropriate motor skills training, does not automatically enhance core stability, or the ability to maintain or adjust posture during execution of an exercise or sports skill” (p. 27). This suggests that in order to increase core stabilization, core-strengthening exercises must be accompanied by sports skill practice.
Unstable resistance exercises might be ineffective for core strengthening for 2 reasons. First, there is difficulty in applying a progressive overload. During the early phases of training, performing only unstable resistance exercises may provide a sufficient overload to the core musculature. However, strength levels may ultimately increase to the point that unstable equipment can no longer be effectively and safely used. This is because a progressive overload can only be achieved by either increasing the resistance or decreasing the stability, both of which can increase the risk for injury.
For example, a typical progression for a shoulder press might be performing the exercise while seated on a stability ball with 2 feet on the floor, then with 1 foot on the floor, and finally while standing on a wobble board (6). When performing exercises such as the squat, dead lift, power clean, standing shoulder press, and push press, the inclusion of unstable equipment has not been shown to be safe or effective.
Second, the use of resistance exercises performed on unstable equipment makes planning a periodized program difficult because a 1 repetition maximum (1RM) cannot safely be determined and strength gains are difficult to measure. Some may argue that these exercises can be performed on “light” days to maintain strength. However, the amount of resistance that can safely be used while training on unstable equipment may not be sufficient to maintain strength gains (4, 17). When considering exercises to increase core strength, free-weight exercises performed while standing on a stable surface may provide the best combination of muscular overload and neuromuscular specificity to sports skills (2, 3, 11, 12, 14, 15, 22, 23, 25, 26).
Although any resistance exercise performed incorrectly can result in injury, the risks involved when performing stable free-weight exercises are minimal. Zemper (27) conducted a 4-year study of weight-room injuries in a national sample of college football teams. The results indicated that the rate of time-loss injuries during weight room activities was less than 1% of the total football injuries reported. The teams sampled performed mostly free-weight exercises while standing on a stable surface.
According to Yessis (25), “Performing free weight exercises on a stable surface is much safer than performing exercises on an unstable surface, where exercisers must give equal or greater attention to maintaining balance instead of exercise execution” (p. 27). Free-weight exercises such as the squat, dead lift, power clean, standing shoulder press, and push press have been shown to load safely the core musculature (27). When these free-weight exercises are performed while standing on a stable surface, many of the core muscles function as stabilizers, either isometrically or dynamically with small concentric or eccentric muscle actions (3,22,25,26). The increased core strength can then be applied to the practice of sport skills to increase core stability and decrease the risk for injuries.
Resistance Training for Sports
Resistance training is an important priority for most sports-training programs. Muscular adaptations are specific to the repetition range and velocity being trained (2, 3, 7, 19, 22). Different sports require different approaches in the way that the muscles are trained. For example, sports such as American football require short duration maximal strength, which necessitates training with relatively heavy loads. Other sports such as cycling require long duration muscular endurance, which necessitates training with relatively light loads (2, 3, 7).
Most sports require individuals to develop strength at both low and high movement velocities, which has been shown to maximize muscular power (12, 23). To develop low-velocity strength, exercises are performed in the same manner as described previously for maximal strength. Because the resistance is near maximal, movement velocity is unintentionally slow. In contrast, to develop high-velocity strength, resistance exercises are performed with submaximal resistance (30–60% of 1RM), and velocity of movement is intentionally fast (2, 3, 19, 22, 26).
Research has repeatedly demonstrated the effectiveness of stable free-weight exercises for enhancing sports-related skills (11, 12, 15, 19, 22, 23). In contrast, not a single study has demonstrated the effectiveness of resistance exercises performed on unstable equipment. Garhammer (11) advocated stable free-weight exercises based on the “multi-joint, multi-muscle group nature of total body free weight exercises, and the resulting neuromuscular specificity and transferability to sport activities” (p. 25). The effectiveness of stable free-weight exercises for enhancing sports skills has been thoroughly reviewed elsewhere (11,14,19,22). However, this article will discuss the key findings from a few relevant studies.
Stone et al. (23) demonstrated that stable free-weight exercises were most effective for increasing vertical jump. Some of the exercises included the push press, squat (full and quarter), and clean-pull. The authors concluded that the stable free-weight exercises exhibited a high degree of mechanical specificity to the vertical jump.
Newton and McEvoy (15) demonstrated that stable free-weight exercises were most effective for increasing throwing velocity. Subjects performed stable free-weight exercises such as the barbell pullover and bench press with a 6–10RM load. The authors concluded that the stable free-weight exercises increased the strength of the muscles involved in the throwing motion, which transferred to greater throwing velocity.
Harris et al. (12) demonstrated that improvement in several sports-related skills was greatest when stable free-weight exercises were performed at both “slow” and “fast” movement velocities. Some of the exercises included the parallel and quarter squat, push press, mid-thigh pull, and bent-over row. Improvement was demonstrated in the following skills: the vertical jump, standing long jump, 10-yd shuttle, and 30-m sprint. The authors concluded that the combination of “slow” and “fast” movement velocities increased muscular power, which transferred to greater improvements in sport skill performance.
Conclusion
Based on the research that currently exists, the optimal approach for enhancing sports performance is to perform free-weight exercises while standing on a stable surface to increase muscular overload and the stimulus for strength gains (2, 3, 11, 12, 14, 19, 22, 23, 25, 26). The increased strength developed in the weight room can then be applied to the practice of sports skills to enhance performance. Resistance exercises performed on unstable equipment have not been proven to be safe or effective in developing the type of balance, proprioception, and core stability necessary for successful sports performance.
Because the majority of sports are played on a stable surface, exercises designed to increase balance, proprioception, and core stability should be performed on a stable surface. Exceptions may include sports such as ice hockey, snow skiing, beach volleyball, and swimming. However, exercises designed to increase balance, proprioception, and core stability for these sports might best be performed on ice, snow, sand, or in the water, respectively (1, 18, 24).
Although there is no guarantee that any resistance exercise will transfer to sports performance, free-weight exercises performed while standing on a stable surface may result in the highest degree of transfer. Exercises such as the squat, dead lift, power clean, standing shoulder press, and push press have been demonstrated to be effective for enhancing performance in several sports-related skills (2, 3, 11, 12, 14, 19, 22, 23, 25, 26). There is little information in the texts and position stands endorsed by the National Strength and Conditioning Association and the American College of Sports Medicine that validates the effectiveness of resistance exercises performed on unstable equipment (2, 3, 14). No study has demonstrated improvement in any sports skill consequent to performing these exercises.
With the lack of research currently available, fitness professionals must be cautious in prescribing resistance exercises performed on unstable equipment. The majority of claims made by proponents of these exercises are currently undocumented (5, 6, 8, 10, 16, 20, 21). Hopefully, this paper will stimulate more research that examines the effectiveness of resistance exercises performed on unstable equipment for enhancing sports performance.
References
1. Adams, J.A. Historical review and appraisal of research on the learning, retention, and transfer of human motor skills. Psychol. Bull. 101:(1) 41–74. 1987.
2. American College of Sports Medicine. Position stand : Progression models in resistance training for healthy adults. Med. Sci. Sports Exerc. 34:(2) 364–380. 2002.
3. Baechle, T.R., R.W. Earle, and D. Wathen. Resistance training. In: Essentials of Strength Training and Conditioning (2nd ed.). T.R. Baechle, and R.W. Earle, eds. Champaign, IL: Human Kinetics. 2000. pp. 395–425.
4. Behm, D.G., K. Anderson, and R.S. Curnew. Muscle force and activation under stable and unstable conditions. J. Strength Cond. Res. 16:(3) 416–422. 2002.
5. Bigatton, J.L. Sports training with a Swiss ball. Ultra FIT. 12:(5) 40–41. 2002.
6. Boyle, M. Functional Training for Sports. Champaign, IL: Human Kinetics. 2004.
7. Campos, G.E.R., T.J. Luecke, H.K. Wendeln, K. Toma, F.C. Hagerman, T.F. Murray, K.E. Ragg, N.A. Ratamess, W.J. Kraemer, and R.S. Staron. Muscular adaptations in response to three different resistance-training regimens: Specificity of repetition maximum training zones. Eur. J. Appl. Physiol. 88:50–60. 2002.
8. Chek, P. Swiss ball exercises for swimming, soccer & basketball. Sports Coach. 21:(4) 12–13. 1999.
9. Drowatzky, J.N., and F.C. Zuccato. Interrelationships between selected measures of static and dynamic balance. Res. Q. 38:(3) 509–510. 1966.
10. Gambetta, V. Let's get physio. For swim-specific weight training, get on the ball. It's easy with our simple but effective physioball routine. Rodale's Fitness Swimmer. 8:(3) 30–33. 1999.
11. Garhammer, J. Free weight equipment for the development of athletic strength and power. Natl. Strength Cond. Assoc. J. 3:(6) 24–26. 1981.
12. Harris, G.R., M.H. Stone, H.S. O'Bryant, C.M. Proulx, and R.L. Johnson. Short-term performance effects of high speed, high force, or combined weight-training methods. J. Strength Cond. Res. 14:(1) 14–20. 2000.
13. Hodges, P.W., and C.A. Richardson. Feedforward contraction of transversus abdominis is not influenced by the direction of arm movement. Exp. Brain Res. 114:362–370. 1997.
14. Kraemer, W.J., and J.A. Bush. Factors affecting the acute neuromuscular responses to resistance exercise. In: ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription (3rd ed.), J.L. Roitman, ed. Baltimore, MD: Williams & Wilkins. 1998. pp. 164–173.
15. Newton, R.U., and K.P. McEvoy. Baseball throwing velocity: A comparison of medicine ball training and weight training. J. Strength Cond. Res. 8:(3) 198–203. 1994.
16. Reid, M. Improving tennis performance using a different type of ball: The Swiss ball. ITF Coaching Sports Sci. Rev. 22:4–6. 2000.
17. Rutherford, O.M., and D.A. Jones. The role of learning and coordination in strength training. Eur. J. Appl. Physiol. 55:(1) 100–105. 1986.
18. Sage, G.H. Introduction to motor behavior (2nd ed). Reading, MA: Addison-Wesley. 1977.
19. Sale, D., and D. MacDougall. Specificity in strength training: A review for the coach and athlete. Can. J. Appl. Sport Sci. 6:(2) 87–92. 1981.
20. Santana, J.C. Stability and balance training: performance training or circus acts?. Strength Cond. J. 24:(4) 75–76. 2000.
21. Santana, J.C. Hamstrings of steel: Preventing the pull. Part II—training the “triple threat.”. Strength Cond. J. 23:(1) 18–20. 2001.
22. Stone, M.H. Literature review : Explosive exercises and training. Natl. Strength Cond. Assoc. J. 15:(3) 7–15. 1993.
23. Stone, M.H., R.L. Johnson, and D.R. Carter. A short-term comparison of two different methods of resistance training on leg strength and power. Athletic Training. 11:(3) 158–160. 1979.
24. Wilmore, J.H., and D.L. Costill. Neurological control of movement. In: Physiology of Sport and Exercise. S. Mauck, ed. Champaign, IL: Human Kinetics. 1994. pp. 44–65.
25. Yessis, M. Using free weights for stability training. Fitness Manage. 19:(12) 26–28. 2003.
26. Zatsiorsky, V.M. Task specific strength. In: Science and Practice of Strength Training. R. Washburn and A. Mischakoff, eds. Champaign, IL: Human Kinetics. 1995. pp. 20–57.
27. Zemper, E.D. Four-year study of weight room injuries in a national sample of college football teams. Natl. Strength Cond. Assoc. J. 12:(3) 32–34. 1990.
Jeffrey M. Willardson is currently completing doctoral studies in exercise and wellness with a concentration in resistance exercise prescription at Arizona State University
1. Adams, J.A. Historical review and appraisal of research on the learning, retention, and transfer of human motor skills. Psychol. Bull. 101:(1) 41–74. 1987.
2. American College of Sports Medicine. Position stand : Progression models in resistance training for healthy adults. Med. Sci. Sports Exerc. 34:(2) 364–380. 2002.
3. Baechle, T.R., R.W. Earle, and D. Wathen. Resistance training. In: Essentials of Strength Training and Conditioning (2nd ed.). T.R. Baechle, and R.W. Earle, eds. Champaign, IL: Human Kinetics. 2000. pp. 395–425.
4. Behm, D.G., K. Anderson, and R.S. Curnew. Muscle force and activation under stable and unstable conditions. J. Strength Cond. Res. 16:(3) 416–422. 2002.
5. Bigatton, J.L. Sports training with a Swiss ball. Ultra FIT. 12:(5) 40–41. 2002.
6. Boyle, M. Functional Training for Sports. Champaign, IL: Human Kinetics. 2004.
7. Campos, G.E.R., T.J. Luecke, H.K. Wendeln, K. Toma, F.C. Hagerman, T.F. Murray, K.E. Ragg, N.A. Ratamess, W.J. Kraemer, and R.S. Staron. Muscular adaptations in response to three different resistance-training regimens: Specificity of repetition maximum training zones. Eur. J. Appl. Physiol. 88:50–60. 2002.
8. Chek, P. Swiss ball exercises for swimming, soccer & basketball. Sports Coach. 21:(4) 12–13. 1999.
9. Drowatzky, J.N., and F.C. Zuccato. Interrelationships between selected measures of static and dynamic balance. Res. Q. 38:(3) 509–510. 1966.
10. Gambetta, V. Let's get physio. For swim-specific weight training, get on the ball. It's easy with our simple but effective physioball routine. Rodale's Fitness Swimmer. 8:(3) 30–33. 1999.
11. Garhammer, J. Free weight equipment for the development of athletic strength and power. Natl. Strength Cond. Assoc. J. 3:(6) 24–26. 1981.
12. Harris, G.R., M.H. Stone, H.S. O'Bryant, C.M. Proulx, and R.L. Johnson. Short-term performance effects of high speed, high force, or combined weight-training methods. J. Strength Cond. Res. 14:(1) 14–20. 2000.
13. Hodges, P.W., and C.A. Richardson. Feedforward contraction of transversus abdominis is not influenced by the direction of arm movement. Exp. Brain Res. 114:362–370. 1997.
14. Kraemer, W.J., and J.A. Bush. Factors affecting the acute neuromuscular responses to resistance exercise. In: ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription (3rd ed.), J.L. Roitman, ed. Baltimore, MD: Williams & Wilkins. 1998. pp. 164–173.
15. Newton, R.U., and K.P. McEvoy. Baseball throwing velocity: A comparison of medicine ball training and weight training. J. Strength Cond. Res. 8:(3) 198–203. 1994.
16. Reid, M. Improving tennis performance using a different type of ball: The Swiss ball. ITF Coaching Sports Sci. Rev. 22:4–6. 2000.
17. Rutherford, O.M., and D.A. Jones. The role of learning and coordination in strength training. Eur. J. Appl. Physiol. 55:(1) 100–105. 1986.
18. Sage, G.H. Introduction to motor behavior (2nd ed). Reading, MA: Addison-Wesley. 1977.
19. Sale, D., and D. MacDougall. Specificity in strength training: A review for the coach and athlete. Can. J. Appl. Sport Sci. 6:(2) 87–92. 1981.
20. Santana, J.C. Stability and balance training: performance training or circus acts?. Strength Cond. J. 24:(4) 75–76. 2000.
21. Santana, J.C. Hamstrings of steel: Preventing the pull. Part II—training the “triple threat.”. Strength Cond. J. 23:(1) 18–20. 2001.
22. Stone, M.H. Literature review : Explosive exercises and training. Natl. Strength Cond. Assoc. J. 15:(3) 7–15. 1993.
23. Stone, M.H., R.L. Johnson, and D.R. Carter. A short-term comparison of two different methods of resistance training on leg strength and power. Athletic Training. 11:(3) 158–160. 1979.
24. Wilmore, J.H., and D.L. Costill. Neurological control of movement. In: Physiology of Sport and Exercise. S. Mauck, ed. Champaign, IL: Human Kinetics. 1994. pp. 44–65.
25. Yessis, M. Using free weights for stability training. Fitness Manage. 19:(12) 26–28. 2003.
26. Zatsiorsky, V.M. Task specific strength. In: Science and Practice of Strength Training. R. Washburn and A. Mischakoff, eds. Champaign, IL: Human Kinetics. 1995. pp. 20–57.
27. Zemper, E.D. Four-year study of weight room injuries in a national sample of college football teams. Natl. Strength Cond. Assoc. J. 12:(3) 32–34. 1990.
Jeffrey M. Willardson is currently completing doctoral studies in exercise and wellness with a concentration in resistance exercise prescription at Arizona State University
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