In many general exercise programs, resistance training participants undertake a variety of prescriptions to either tone up their muscles or increase their muscle size. There is a plethora of magazines available that focus on the concept of increasing muscle size both through the manipulation of diet and exercise programming in combination with the additional use of nutritional supplements. Consequently, information abounds that at times is controversial, attracting widespread debate. Before a consensus of opinion can be developed, research on hypertrophy and hyperplasia needs to be examined to form at least a base opinion as to the mechanism of hypertrophy and the effect that the manipulation of training variables has on this mechanism.
This issue of the FIA Research Review examines the process of muscle hypertrophy and its application in general exercise prescription by examining skeletal muscle adaptations as a result of hypertrophy, hormonal influences, training volume, specific muscle contractions and hypertrophy responses and exercise prescriptions.
- Skeletal Muscle Adaptations during Early Phase Heavy Resistance Training in Men and Women, Staron, R. S. , Karaponda, D. L. , Kraemer, W. J. , Fry, A. C. , Gordon, S. E. , Falkel, J. E. Hagerman, F. C. & Hikida, R. S. (1994). Journal of Applied Physiology 76 (3) : 1247-1255.
It has been reported that both hypertrophy and neural responses contribute to increases in strength. Neural responses include motor unit synchronization, neural activation, increased excitability of motor end plates and decreased inhibition of the Golgi tendon organs while hypertrophy involves the increase in size of the muscle fibers and perhaps some hyperplasia. It has been generally accepted that the initial strength responses occur from the neural adaptations followed by muscle hypertrophy responses. Recently this has been challenged with reports of significant hypertrophy in all major fiber types after just six weeks of high intensity training. The purpose of this study was to investigate the time period of muscular responses every two weeks during an eight week high intensity heavy resistance training program in trained and untrained subjects.
Thirty-three subjects volunteered for this study. Thirteen men and eight women comprised the trained group while seven men and five women comprised the untrained group who acted as a control group. Body composition, hormone analyses, muscle biopsies, myosin heavy chain analyses and serum collection was conducted every two weeks of the eight-week program. The heavy resistance-training program consisted of three lower limb exercises performed twice per week. Workouts consisted of two warm-up sets followed by three sets to failure of either six to eight repetitions for each of the three exercises.
Women increased strength significantly in leg extension and squat while men increased strength in squat and leg press. There was a decrease in Ftb after two weeks in women and four weeks in men, while testosterone levels increased in men after four weeks and cortisol decreased after six weeks. No other significant changes occurred.
Application for the Fitness Instructor
- Studies have reported a significant increase in the size of all muscle fibers of young and elderly women after participation in a 20 week high intensity resistance training program. It was also demonstrated that there was an apparent fiber conversion from Ftb to Fta. This is somewhat unusual as this is a typical response of endurance training.
- It has been suggested that after a single bout of heavy training there can be an increase in protein synthesis for up to 24 hours. This can ultimately lead to an increase in the number of actin and myosin filaments within the sarcomere of the affected fibers. This process can show significant cross sectional changes in the muscle within eight weeks of training.
- Even though the addition of actin and myosin takes up to eight weeks to initiate, the conversion of Ftb to Fta appears to occur much quicker in women. However the general strength changes are very similar for men and women during the first eight weeks of training.
- One specific gender difference observed was the increased testosterone and decreased cortisol in men which was not apparent in women. The increases in these hormones suggest an improved environment for muscle growth.
- While neural factors still appear to be very important in the initial stages of a heavy resistance training program muscle specific cross sectional responses cannot be underestimated.
- The Effect of Voluntary Effort to Influence Speed of Contraction on Strength, Muscular Power and Hypertrophy Development, Young, W. B. & Bilby, G. E. (1993). Journal of Strength and Conditioning Research 7 (3) : 172-178.
It has become apparent over many years that to improve strength and power required different exercise prescriptions. Sports such as sprinting, jumping, throwing and kicking require high-speed actions and maximum force generation and are generally trained in power activities. Prescriptions to develop power have generally involved loads of approximately 20 to 80 percent of maximum strength performed with fast contractions. Strength is developed at 90 percent of maximum strength in a slower more concentrated contraction.
More recently this prescription has been challenged with some studies reporting improvements in power with heavy loads and slow contractions. A study by Schmidtbleicher and Haralambie trained subjects on 90 to 100 percent of maximum strength + 1kg performing sets of one to four repetitions. The subjects improved in strength, rate of force production and speed of the electrical impulse. It has been further suggested that if maximum effort is used the activation pattern of the muscle is the same regardless of the speed of movement. Perhaps the external speed of the limb is less important than the speed of the muscle contraction that is controlled by the central nervous system.
The purpose of this study was to determine the effects of voluntary effort on strength, muscle power and hypertrophy in untrained subjects.
Eighteen subjects who were untrained and free of injury volunteered for this study.
Subjects were tested for height, weight and absolute one Repetition Maximum on a machine squat. Subjects were assigned to one of two experimental groups. Both groups completed four sets of eight to 12 repetitions at an eight to 12 RM, with a rest of three minutes between sets, three times per week for seven and half weeks on half squat exercise. The fast group completed the sets in a fast controlled upward motion while the slow group completed the sets in a slow and controlled upward and downward motion, minimizing acceleration. The exercise was supervised under close supervision at all times. Subjects were not permitted to undergo any additional exercise that may train the lower extremity.
All subjects were tested pre- and post-program on vertical jump, one RM, peak isometric force, middle and distal thigh circumference, rectus femoris and vastus intermedius thickness and body weight.
The fast group (68.7 percent) improved more than the slow group (23.5 percent) in maximum rate of force development (power), while the slow group (31 percent) performed better than the fast group (12.4 percent) in absolute isometric strength. Both groups increased similarly for hypertrophy. There was no difference in one RM for either the slow or fast group.
Application for the Fitness Instructor
- The investigators reported significant gains in strength, power and hypertrophy concurrently in untrained subjects after seven and half weeks participation in a resistance training program. Consequently, initial gains for untrained subjects may be general in nature.
- The results suggest that a greater improvement in power can occur with faster movements when compared to slower movements. This may indicate that these initial power gains in beginners can be substantially influenced by neural factors.
- The fast group and the slow group showed no significant difference in one RM strength measures. An examination of the raw scores still indicated that the greatest values were reported in the slow group. If little difference exists between both speeds, because of safety the slow method should be prescribed first for beginners. Isometric gains were significantly greater in the slow group than the faster group. This would indicate that slow speed training increases isometric strength while faster speed training increases power for lower body exercises. Strength gains can occur irrespective of the speed that training is performed at.
- Both the fast and slow training methods produced gains in muscle hypertrophy. The highest values were reported in the vastus intermedius than the rectus femoris. This may reflect the individual involvement of each of these muscles. Overall strength gains were greater than hypertrophy gains. This may indicate that neural factors are again more prevalent in the early stage of the program for beginners.
- Seven and half weeks of resistance training either using fast or slow methods appears to be sufficient to induce significant hypertrophy changes in beginning exercisers. With further participation, it is theorized that the slow training method would achieve greater gains due to the increased length of time the muscle would be placed under tension.
- The Effect of Weight Training Volume on Hormonal Output and Muscular Size and Function, Ostrowski, K. J. , Wilson, G. , Weatherby, R. , Murphy, P. W. & Lyttle, A. D. (1997). Journal of Strength and Conditioning Research 11 (3) : 148-154.
Muscle hypertrophy is often pursued by both athletes and recreational exercise enthusiasts alike. Athletes seek hypertrophy to increase strength and power, while exercisers desire the "look." Intensity and volume of effort have long been recognized as crucial to the hypertrophy response. However, controversy exists as to the best prescription for muscle hypertrophy. Scientific studies have suggested that one to four sets per muscle group per session is highly effective while body builders have typically performed nine to 24 sets per muscle group. Consequently it is generally accepted that three to six sets per exercise for three to four exercises using a load of 60 to 80 percent max may represent the best hypertrophy prescription.
The purpose of this study was to examine the effects of three specific volume methods on hypertrophy, strength and power in average trained subjects.
Thirtyfive males were selected for this study. Each had been training for between one to four years and was able to squat and bench press 130 percent and 100 percent of their body weight. Subjects were assigned to one of three groups: a low volume group who performed three sets per muscle group, a moderate volume who performed six sets per muscle group and a high volume group who performed 12 sets per muscle group.
The program was conducted for 10 weeks, with subjects training to fatigue in each set four times per week. Each training session consisted of a variety of exercises, each performed once per week.
Each subject was tested for hypertrophy by an ultrasound procedure, strength by a one repetition maximum on squat and bench press, peak power by vertical jumps and bench press throws and testosterone and cortisol changes through urine testing.
All three training volumes increased power, strength and power over the 10-week training program. There was no reported change in testosterone or cortisol levels in any of the volume groups.
Application for the Fitness Instructor
- This study reported that there were similar increases in strength and power regardless of the training volume (three, six or 12 sets). In other words, there appears a training volume threshold where additional volume is no longer an advantage. By decreasing the training volume by almost half, strength and power responses can be maintained.
- Over a 10-week program of four times per week, there was no difference in muscle hypertrophy between performing three, six or 12 sets of the same exercise. This finding contradicts some of the currently available literature as it has often been postulated that time under tension of a muscle is a key stimulus for muscle growth. Based on this recommendation, an increased muscle tension for a longer duration is supposed to produce the best adaptation. An increase in muscle hypertrophy is based on the disruption of myofibrils forcing an increase in the deposit of contractile protein increasing the size and number of myofibrils. The present study indicates that programs of varying volumes will all increase muscle hypertrophy at a similar rate. This indicates that further overload through additional volume at a high intensity will not necessarily increase the size of the muscle to a greater extent.
- The results of this study indicated that average trained subjects did not significantly increase testosterone and cortisol levels after 10 weeks of high intensity training. This is in support of a study completed by Hakkinen who reported that athletes can increase muscle strength without an increase in hormonal levels.