Health Benefits of Strength Training

Article by Ed McNeely and David Sandler

There are many definitions of health ranging from the absence of disease, to optimal mental, physical, social and spiritual functioning and every thing in between. While health can be a very abstract topic by any definition strength training plays an important role in the development and maintenance of health. Strength training can improve confidence and self image and provide opportunities for social interaction as well as improve many physical characteristics that are often linked to the development of disease later in life. The focus of this chapter will be on the physical adaptations to strength training that can lead to improved health like changes in blood lipid profiles, heart function, weight loss, and bone density.

 

 Strength Training and Body Composition

 

Industrialized societies are currently facing an obesity epidemic brought on by a combination of an over consumption of food and a lack of exercise. While participation in youth sports leagues has remained relatively constant competitive sport opportunities are less available for people once they finish high school often causing a drop in physical activity levels that carry through young adult hood into later life. Life long fitness activities can have a positive effect on body weight in later life if the foundation for their participation is laid in adolescence. Strength training in particular can have a tremendous impact on body composition.

 

 

Research on strength training and decreases in fat mass have yielded mixed results. Sedentary individuals who take up strength training typically will see a decrease in body fat levels and an increase in lean muscle mass, this is particularly true for older adults.

Active people who add strength training to their programs see an increase in muscle mass but only a transient change in long term fat levels, following an initial period of fat loss there is an increase in fat levels back to the initial starting level. This is probably because active people adjust their eating patterns to compensate for the increased energy demands of the strength training program.

 

An imbalance between the amount of energy taken in and the energy expended results in weight loss or weight gain. Strength training sessions affect energy balance in two ways; the caloric cost of a strength training session is related to the total amount of weight lifted. This means that high volume training sessions where lots of reps are done with lighter weights require more energy than high intensity training sessions where heavy weight are used for relative few reps.

 

During strength training type exercise anaerobic metabolism meets most of the energy demands; little fat is oxidized during the training session. To reduce body fat there must be periodic changes in carbohydrate and fat balance. If a sufficient amount of carbohydrates are used during strength training a carbohydrate imbalance may exist which would favor the oxidation of fat after exercise. Post-exercise fat oxidation is greater in anaerobic training than in low intensity endurance training. 

 

You don’t have to look any further than a competitive bodybuilder or football player to see that one of the most obvious changes that occurs with strength training is an increase in lean body mass. It is through this that strength training has the potential for treating obesity. Basal metabolic rate is the amount of energy required to maintain the physiological processes that are necessary for life and body function. Resting metabolic rate is the amount of energy used at rest. Muscle mass accounts for about 35% of resting metabolic rate; an increase in muscle mass increases resting metabolic rate and the amount of energy that can be consumed without increasing fat stores. Increasing muscle mass is not a quick solution to obesity because the amount of true muscle tissue that can be gained in the course of a year without the use of anabolic steroids is only about five pounds but this can add up over the time. Except during an adolescent growth spurt, when someone gains 20 pounds over a summer as the result of a strength training program only a portion of that weight gain is true muscle tissue the rest is stored carbohydrates, intramuscular fat and a substantial amount of intramuscular water.

 

Some guidelines for designing a program to help alter body composition are:

 

As mentioned earlier, the caloric cost of strength training is related to the total amount of weight lifted. High volume training results in a greater total amount of weight lifted, increasing energy expenditure and promoting muscle hypertrophy.

 

You can perform high volumes of work in short periods of time in circuit training. Because rest time between exercises is reduced, there is a greater density of work and more calories are burned per unit of time. Sequencing upper and lower body activities will distribute fatigue and allow adequate recovery of each muscle group between circuits.

 

In order to stimulate muscle growth and increase metabolic rate adequate tension and resistance must be placed on the muscles. Hypertrophy seems to be developed most effectively when resistances of 60%-80% of 1RM are used for multiple sets. While lower resistances may allow a higher total volume of work they are less effective at creating hypertrophy, which is important for long term weight loss.

  

Blood lipid levels, Cholesterol and triglycerides are a critical risk factor of coronary heart disease. Serum cholesterol levels have been associated consistently with the development of heart disease. Controlling cholesterol levels, either increasing HDL, the good cholesterol or decreasing LDL, the bad cholesterol, can lessen the incidence of heart disease.

 

Strength training’s role in altering blood lipid profiles is controversial.  Several cross-sectional studies reveal unfavorable changes in blood lipid profiles including suppressed HDL-cholesterol and elevated total cholesterol to HDL-cholesterol ratios. However, these studies have been criticized because they did not control for age, body fat, and training regimen. Many studies also did not control for anabolic steroid use. Steroid use is common among weightlifters, bodybuilders and powerlifters and has been shown to decrease HDL-cholesterol levels. In more controlled studies the effectiveness of strength training for altering blood lipid profiles seems to be closely related to program design.

 

Fleck (1992) suggests that high volumes of strength training, 8-12 repetitions per set, may benefit blood lipid profiles more than low volumes, 1-6 repetitions per set. Goldberg, Elliot, Schutz, and Kloster (1984) found decreases in total cholesterol, LDL-cholesterol and LDL/HDL cholesterol ratios after 16 weeks of strength training using sets of 3-8 repetitions. lessing et al. (1987) and Johnson et al. (1982) noted significant decreases in total cholesterol/HDL-cholesterol ratios and increases in HDL-cholesterol after 12 weeks of strength training. In both studies the greatest change in serum lipids occurred during the highest volumes of training. Wallace, Moffatt, Haymes, and Green (1991) found acute increases in HDL-cholesterol 24 hours after a strength training session involving sets of 8-12 repetitions and no changes in HDL-cholesterol after low-volume training sessions, i.e., sets of 1-5 repetitions.

  

The heart consists of four chambers, the left ventricle, which circulates blood the rest of the body, the right ventricle which circulates blood to the lungs, the right atrium which receives blood from the body, and the left atrium which receives oxygenated blood from the lungs.

 

One of the goals of exercise is to increase the efficiency of the heart, improving the circulation of blood throughout the body by increasing stroke volume, the amount of blood pumped with each beat, decreasing resting heart rate and improving cardiac output, the amount of blood circulated in a given period of time.

 

Weight training is generally believed to be of little benefit in modifying the risk factors of cardiovascular disease but this opinion, however, is slowly changing as more research reveals that the heart, like other muscles, adapts to the stress of weight training. Specifically, the left ventricular (LV) wall thickens to adapt to the stress allowing the heart to beat more forcefully and eject more blood with each contraction. Researchers have found that compared to untrained controls, national and international weightlifters were found to have a greater degree of LV wall hypertrophy and LV mass in several studies. In a training study, researchers found increases of 10% in the thickness of the LV wall.

 

Changes in left ventricle function and size are not the only cardiac adaptations to strength training. There is also a decrease in resting heart rate of 3-11% associated with starting a strength training program and resting blood pressure has been found to drop by 3-4% compared to pre training levels.

 

This does not mean that strength training can replace aerobic training as a means of improving cardiovascular fitness. The adaptations to the two type of training are very different. Where strength training seems to increase left ventricular wall thickness aerobic training increases the size of the chamber. Whether one type of training is better than another is still being debated. The only sure thing is that either type is better than no training.

 

Increases in LV mass appear to be a function of exercise intensity. High intensity strength training increases blood pressure during exercise. Elevated blood pressure increases LV mass and thickens the LV wall. Most types of strength training do not appear to affect the size of the heart chamber. However, some types of high volume bodybuilding programs with limited rest periods may increase the chamber’s size. Some guidelines for improving cardiovascular function and blood lipid profiles through weight training are:

 

Circuit weight training with short or no rest periods increases the aerobic demand of the exercise. In some cases oxygen demand could get as high as 55% of VO2 max, high enough to create cardiovascular adaptations.

The volume per set and total work volume should be kept high. Use 4-5 sets of 8-12 reps to stimulate both improved cardiac function and positively alter blood lipid profiles.

 

 Strength Training for Increased Bone Density

Osteoporosis is a problem in today’s society, affecting millions of people every year. While low bone density can affect both genders it is more prevalent amongst females and often starts during the teenage years. Bone density is most effectively increased before the age of 30 after this age a natural decline in bone density makes it difficult to see a net accumulation of bone mineral. Addressing the issue of bone density during the teenage years can help prevent future complications that may arise from osteoporosis.

 

We have known for more than a century that there is a relationship between mechanical loading and bone hypertrophy. Certain types and volumes of physical activity increase bone mineral density (BMD) while immobilization or bed rest decrease bone density. When a force is applied to a material such as bone there is a certain amount of bending or deformation. The amount of bending compared to its original length is known as strain. When muscles pull on bones with sufficient force strain is created where the muscle attaches to the bone. Strain and rate of strain are the two most important factors responsible for increased bone density through exercise. Strength training, when done at a high enough intensity, can provide sufficient strain to increase bone density but it is not the most effective means of increasing bone density; jumping, because it creates a higher strain and rate of strain, has been shown to be the most effective form of exercise for increasing bone density. A recent study of adolescent girls found that adding 10 maximal effort jumps to a PE class 2-3 times per week is sufficient to increase bone density in the legs, hips and spine. While jumping is the fastest way to increase bone density weight training has the advantage of incorporating the whole body. Bone density increases are very specific to the muscle groups and body parts used in the exercises. For example squats will increase bone density of the head of the femur and lumbar spine but do little for bone density in the wrists, cervical, or thoracic spine while bench pressing increases bone density of the wrists and clavicles but not in the lower body.

 

Many popular magazines and other publications promote weight bearing exercise such as walking or jogging for improving bone density. While this is an acceptable prescription for older adults who have been sedentary for long periods of time it is insufficient to improve BMD in younger people. In fact, volumes of aerobic training in excess of eight hours per week can result in decreased bone density. This is one of the reasons for keeping strength training in the programs of endurance athletes all year round.

 

A well balanced program begun during adolescence can reduce or eliminate the effects of osteoperosis. Consider these guidelines for designing programs to improve bone density.

 

Increase resistance progressively. This is necessary because for bone to form it requires a minimum amount of strain. Once a bone adapts to a given strain level, the stimulus for bone to form is removed and a higher strain level becomes necessary for it to adapt further. Increase the resistance used at regular intervals, every 2-3 weeks to ensure continued progress.

 

While it is common for strength training exercises to be done in a slow controlled fashion this is not the best approach to increasing bone density. Higher speed movements and the attempt to move at a high speed create higher rates of strain and improves the effectiveness of strength training for increased BMD. The addition of Olympic style lifts to the program is an excellent way of increase the rate of strain. Olympic style lifters have been shown to have some of the highest levels of bone density in athletes.

 

Increases in BMD during strength training are related to the load placed on the muscles around the bone. Evidence supporting this hypothesis comes from the lack of adaptation in total body BMD and lack of increased BMD in bones surrounded by muscles that do no act as prime movers. Changing the distribution of strain is important to develop new bone and may be more critical than the amount of strain. Changing exercises frequently, and subsequently the muscles used, will help change the distribution of strain and ensure that a wide variety of muscles act as prime movers.

 

There is a threshold below which the resistance and strain placed on the bone are insufficient to increase bone density. Current research suggests that this around 70% of 1RM and that exercise below this intensity will have limited effects on bone density.

 

The bone remodeling cycle lasts four to six months. This is the minimum period of time needed for BMD to change significantly. Training must be done at least three times a week for a year to see measurable increases in bone density. Ideally strength training becomes part of an active lifestyle that will help maintain bone mass through adolescents into adult hood and old age.

 

Strength train is now an integral part of most sport and fitness programs. The reason most cited for including strength training is increased strength and power but strength training can also play a role in injury prevention.

 

Many assume that higher levels of strength are key on preventing injury. This could not be further from the truth. Most research indicates that stronger athletes actually have higher injury rates than weaker athletes, possibly because they are capable of pushing themselves further and take more risks because of their strength.

 

Strength training can help prevent injury by correcting muscle imbalances. Muscle imbalance are differences in strength between the right and left side of the body or a difference in strength between agonists muscles, the muscles that make a movement happen and antagonist muscles, those on the opposite side of the body that help stop the movement.  When these imbalances occur the body does not move efficiently and bones and joints are pulled unevenly, increasing the risk of injury. When differences between sides of the body are greater than 5% the risk of injury increases by 20 times.

 

Muscle imbalances are a serious problem for many athletes. Sports such as baseball, hockey, and golf all feature unilateral rotations which develop one side of the body more than the other. Most sports have some sort of unilateral movement that will create a strength imbalance. Even everyday living can cause muscle imbalances as almost everyone tends to favour one side of their body over another.

 

Every strength training program should account for the potential muscle imbalances that everyone has and try to correct them. Consider these guidelines when designing strength training programs to help prevent injuries:

 

When you throw a ball it is the muscles on the front side of the body that create the throwing motion and it is the muscles on the back side of the body that stop the arm before it gets injured. All movements work in these pairings and the training program should address these pairings. If you are going to do bench press, which works the chest and pulls the arms forward you need to do an exercise like bent lateral raises that will work the muscles of the upper back that pull the arms backward.

 

Since bilateral asymmetries have been implicated as an injury risk factor, dedicate periods in the year to correcting these imbalances. When right and left sides are trained together (using barbells or exercise machines), the stronger side can take a larger proportion of the load.  Training the sides independently helps to ensure that both sides work equally.

 

Exercises such as squats, cleans, bench presses, and deadlifts are commonly used in programs designed to improve athletic performance. Though these exercises are key to a training plan, give attention to specific exercises for the muscles that stabilize joints like the rotator cuff, the glutes, leg abductors and adductors.

 
Use Barbell and Dumbells instead of machines

Machines work through a predetermined range of motion and require no work to stabilize the resistance. Free weight exercises force you to work on balance and stability. This will increase the strength in secondary muscles that help prevent injury.

 

Strength imbalances can become a serious long term problem if they are not corrected and can lead to chronic injury and pain. Addressing them early in your lifting career will help you stay injury free.

 

 Conclusion

 

Strength training is often viewed as a means of altering physical appearance or improving athletic performance but it can be far more. As a lifelong activity strength training is an excellent tool for promoting health by altering blood lipids, treating obesity, decreasing the chance of injury , increasing bone density and improving heart function.