muscle Hypertrophy (from nasm)

jacky

Hypertrophy

For many, a desired outcome of resistance training is growth of muscle tissue. This hypertrophy and resulting strength enhancement accompanies long-term resistance training. Many realize that the initial rapid increase in strength when a novice begins a resistance training program is due in large part to neural adaptations increasing muscle fiber recruitment. Hypertrophy, according to genetic considerations, follows. The following papers, reported chronologically, met the inclusion criteria about the nature of the hypertrophic response to resistance training.

One of the long-standing questions of the latter 10-20 years of the 20 th century surrounded the question of hypertrophy (increasing fiber size) or hyperplasia (increasing fiber number). Some early work in animals suggested a major role of hyperplasia leading to some investigations on humans using the muscle biopsy technique (for fiber area) and imaging (for muscle area). Dividing muscle area by fiber area was a gross method of estimating fiber number. McCall (1996) attempted to determine the interaction of hypertrophy and hyperplasia on recreationally trained male lifters. Fifteen of 28 applicants were selected, but only 12 completed the study. Training was conducted 3 days per week emphasizing all major muscle groups, but 4 exercises involved elbow flexion--the muscles of interest. The resistance was 10RM and once a subject could execute the lifts 10-12 times without assistance, 5% was added. Strength (as 1-RM) was determined every 3 weeks during the 12-week study. Diet was evaluated to ensure similar protein intake throughout the study (1.5g/kg mass). Areas of the arm were determined pre and post training using MRI while needle biopsies of the biceps were used for cellular dimensions.
The 12-week program showed no changes in mass or sum of skinfold thicknesses. Protein intake remained constant at 15.5-17.5% of total calorie intake, with only one subject needing to increase protein calories. Forearm flexion strength was determined using a preacher curl exercise and 1-RM showed consistent increases every three weeks. Each test period was significantly greater than pre-training only. The observed increases were not different from one session to the next. The data were presented in bar graphs so effect sizes could not be accurately determined. Overall arm cross sectional area was significantly increased by 14% (ES=.90). Individually, the biceps brachii increased by 12% (ES=.55), the brachialis by 7.5% (p=n.s., ES=.51), and the triceps by 25% (ES=.95). Both type I (+10%) and type II (+17%) fiber types significantly increased in area. A final result was capillary density. Capillaries per fiber increased for both type I fibers (+13%, ES=.98) and for type II fibers (22.6%, ES=1.51). The number of fibers counted per biopsy sample was small, around 120-130 fibers.
Despite the small numbers in this study, there were some interesting findings. The observed change in muscle size was due mostly to hypertrophy. With both fiber types increasing in area, the greatest improvement was in the type II fibers. Overall, there was no evidence of hyperplasia, although there was the rare subject who did show some evidence of hyperplasia. One of the problems in hyperplasia studies in humans is the small number of fibers counted. Stable estimates of fiber number require many more cells. Also of interest was the increase in capillaries per fiber in rough proportion to fiber area.
There is some agreement that adaptations to resistance training programs can be influenced by the experience of the subjects. The prior study was conducted on college age males with recreational lifting experience. Chilibeck (1998) studied 29 young women with "minimal strength training experience." Their goal was to determine how much hypertrophy contributes to the increase in strength. Their project was unique in that it compared simple (one joint) vs. complex (multi-joint) movements. The training program was twice a week for 20 weeks. The simple exercise was the forearm curl while the complex lifts were the bench and leg presses. Other upper and lower extremity exercises were included. The intensity of the upper body exercises was 6-10RM and 10-12RM for the lower body exercises. An additional factor in the project was a "whole" (all exercises performed on two days per week) or a "split" (half on Monday-Wednesday and other half on Tuesday-Thursday) routine. A 1-RM for the bench press, leg press, and the forearm curl was used to verify change in strength. Muscle mass was imaged using DEXA. Data was collected pre training, mid (10 weeks), and post training (20 weeks). The training group consisted of 19 women with the remaining 10 serving as controls. The training group was further divided for comparison of whole vs. split training routines that was reported in another outlet (Calder, 1994). All assignments were random.
Forearm curl, bench, and leg press strength were significantly increased at each testing period. For example, curl strength increased by 50% from pre to mid training and 15% from mid to post training. Bench press strength increased by 22% and 8%, respectively. Leg press strength increased by 13% and 7.5%, respectively. The improvement in muscle mass of the arms were significant only from pre to mid training (7.5%) while increases on trunk (2.7%) and leg mass (2%) occurred only from mid to post training. The data were presented as bar graphs so effect sizes could not be determined. The increase in muscle mass "correlated poorly" with the change in strength.
The project has limited generalizability as the subject sample was female with limited resistance training experience and the results might have differed in male subjects, for subjects with more extensive resistance training experience, or a different training prescription. Regardless, the rapid hypertrophy of the more simple exercises vs. the later hypertrophy of the more complex exercises suggests there was some prolonged neural adaptation for the complex exercises. The simpler, single joint exercise showed the more rapid adaptation while the greatest adaptation in the complex exercises happened later.
With his prior study showing the role of hypertrophy in the adaptive response, the next paper from McCall and colleagues (1999) analyzed blood drawn from the subjects in their 1996 study to learn more about the role of anabolic hormones in the hypertrophic response to a resistance training program specifically designed to induce hypertrophy. This small study of recreational resistance trained college men followed the same protocol of their 1996 project outlined above, only in this project blood samples were drawn to analyze for growth hormone, insulin-like growth factor (IGF-1), testosterone, cortisol, and sex hormone binding globulin (SHBG). Resting values were determined pre and post training. Responses to exercise were obtained before, during, and after the 10 th and 20 th exercise session.
The strength and cross sectional adaptations are discussed in the 1996 paper (above). In this paper, an untrained control group of eight was added. There were no changes, other than a decrease in cortisol, in resting hormone concentrations before or after training or between groups. Hormonal concentrations of IGF-1, testosterone, and SHBG (after correction for exercise-induced decreases in plasma volume), were unaffected by exercise while growth hormone was increased in response to exercise. Cortisol was elevated post exercise. There were no differences in the pattern of response between the 10 th and 20 th week.
There were few correlations between the panel of hormones and the resulting muscle and fiber hypertrophy reported in their 1996 paper. The only correlation was between exercise-induced growth hormone concentrations and increases in muscle fiber area. The authors postulated that the development of muscle hypertrophy from resistance training could be influenced by the repeated exercise-induced elevations of growth hormone.
Most of the papers reported here are longer term studies. Blazevich and colleagues (2003) conducted a short-term project of only five weeks. They pointed out that most of the earlier work show improvements, but the length of the studies are such that even mid-study measurements would likely miss changes that might occur during a short term training period. A unique feature of this project was the attempt to determine muscle fascicle angle, a factor in force output.
They started with 30 competitive athletes, but injuries forced seven to drop out leaving 23 (8 women) who completed the study. All subjects competed in team sports and had performed resistance training for at least 3 months prior to enrolling in the study. Before the project began, they trained in their sport twice per week, played one match per week, and did two resistance training sessions per week. During the study, they performed a 4-week "standardization" period of resistance (2d/wk) and sprint/jump training (2d/wk). After this phase, the subjects were randomly assigned to a squat, a hack squat or a sprint/jump training group where each performed exercises specific to their assignment. The subjects in the two resistance training groups trained twice a week with a heavy (3 sets, 6RM) and a light (squat jumps, isometric contractions at 30-50% max). The sprint/jump group trained with multiple 20m and 30m sprints along with one and two-legged counter movement jumps. Sprint speed (10m and 20m), one and two-legged counter movement jumps, 1-RM squat and hack squat, force during loaded (30% and 60% of isometric maximum) jump squats, and isokinetic knee extension were tested before and after the training period. Fascicle angle and length within the vastus lateralis and rectus femoris was determined by ultrasound.
While there were significant increases in performance on selected variables (10m, 1 and 2 legged isometric hack squat, force during loaded jump squats), there were no group differences suggesting all groups responded to a similar magnitude. Isokinetic torque was unchanged with training. There was a reduction in fascicle angle in the distal vastus lateralis in the sprint/jump training group alone. Fascicle angle increased in the proximal vastus lateralis in the squat and hack squat group, but decreased in the sprint/jump group. Fascicle angle also increased in the distal rectus femoris group in only the hack squat training group. Increases in fascicle length were more commonly seen in response to sprint/jump training. Muscle thickness was increased with training, but there were no group differences.
The authors felt it was significant that they found changes in muscle fascicle architecture in such a brief training study and that the changes were specific to the type of training. Sprint/jump training (i.e., high velocity training) led to decreases in fascicle angle and increases in fascicle length while resistance training increased the fascicle angle without changing fascicle length. By individual muscle, the monoarticular vastus lateralis displayed greater changes in architecture than the biarticular rectus femoris. Based on the fundamental differences in the training programs, it appeared that the force-velocity nature of the individual training exercises had a specific effect on muscle fascicle architecture. Despite the changes in architecture, there was little effect on performance between the groups.
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In the early to middle 1980's came reports that concurrent strength and endurance training interfered with the adaptations of each other. Subsequent studies either confirmed or failed to find this same interference effect. With some sports and occupations requiring both strength and endurance, Hakkinen (2003) looked at combined strength and endurance training vs. strength training during a long term study.
This is another paper with WJ Kraemer as an integral part of the research team. The study began with 32 healthy men from Finland (age=37.5y) enrolling, but five had to withdraw. A total of 16 men were in the strength training only group and 11 in the combined group. The study was 21 weeks long with testing, pre training, and then every 7 weeks. Strength was determined isometrically and concentrically for the hip, knee, and ankle extensors and knee flexors. A 1-RM was obtained for each movement. MRI was used to determine muscle cross sectional area of the right quadriceps. A cycle ergometer was used to measure aerobic power as well as aerobic and anaerobic thresholds. Numerous other mechanical measures were obtained (e.g., EMG, rate of force development, and more), but will not be reported here.
The strength aspect of the training focused on the quadriceps. Training was conducted twice a week. Additional upper body and trunk work was also performed. The training protocol was based in 7 week segments. During the first 7 weeks, the subjects performed 3-4 sets of 10-15 repetitions at 50-70% of 1-RM of each exercise. The loads were increased by about 10% for the next 7 weeks with a slight reduction in the repetitions. For the final weeks, the loads were again increased with corresponding decreases on repetitions. A three-week taper began at week 18.
Endurance training was also conducted twice a week. During the first 7 weeks, the subjects performed cycle ergometer exercise for 30 minutes just under their aerobic threshold intensity. During the next 7 weeks, on the first endurance day of the week, they cycled for 45 minutes at progressively increased intensities (15 minutes below aerobic threshold, 10 minutes between the aerobic and anaerobic thresholds, 5 minutes above the anaerobic threshold, 15 minutes below the aerobic threshold). The second endurance day they cycled for 60 minutes below the aerobic threshold. The goal of the final 7 weeks was to increase cycling speed through a series of high intensity intervals one day a week and to increase endurance with 60-90 minutes at the aerobic threshold on the other day.
Bilateral, concentric leg extension1-RM increased in parallel in the two groups, each by 21-22%. Uni and bilateral isometric leg extension force showed similar increases. The increase in quadriceps cross sectional area averaged 6% and 9% in the strength and strength/endurance groups, respectively. At the fiber level, the cross sectional area of the type I, type IIa, and type IIb increased by 47%, 26%, and 37%, respectively for the strength trained group and by 13%, 23%, and 31%, respectively for the strength/endurance trained group. Of the mechanical data, only maximum rate of force development and corresponding EMG in the strength/endurance group were below that of the strength group and these could affect explosive strength. Endurance, as VO2max, increased by 18.5% in the strength/endurance group, maximal power output increased by 17% as well as the work loads for the aerobic (+16%) and the anaerobic (+14%) thresholds.
The authors felt that their data did not support the concept that concurrent endurance training "interfered" with strength enhancement or hypertrophy. Both strength and endurance increased by nearly similar magnitudes. However, the authors point out that there may be a potential for interference should the intensity of training be greater than that used in this project. In this case, rapid strength gains might occur early in the training program, but then show only limited improvements later a program. They also questioned a potential for interference in explosive power output based on some of their neural activation data. One finding that did have very practical significance was that endurance could improve training only twice per week.
Because of the numerous training variables in resistance training, it is difficult to design a single study that will allow direct comparison of all the possible variables; it would just be too big a training study. What Kraemer et al (2004) tried to do was compare a program focusing on hypertrophy vs. a program focusing on strength/power with a further factor of transfer (upper body only vs. whole body training). They chose to study previously untrained women for 6 months. Prior work on this population had shown training plateaus at around 12-15 weeks of training and the authors were curious if their periodized program might continue to stress the women sufficiently to continued improvements.
A total of 85 women completed this 6-month training program. These untrained, but active college women, were randomly assigned to one of four groups or to a control group. One factor was training emphasis (power or hypertrophy) and the other was training location (upper body only, total body) giving four groups: total body power (TP, n=18), total body hypertrophy (TH, n=21), upper body power (UP, n=21), and upper body hypertrophy (UH, n=19). The control group had six subjects. Body composition was estimated using skinfolds; muscle and limb cross sectional areas (mid thigh, mid upper arm) was determined using MRI images. Squat and bench press 1-RM were determined. Power was measured with the jump squat and the ballistic bench press. The training programs were all linear periodized in design; the details and lifts used are beyond the scope of this paper. All tests were conducted pretraining, then after 12 and 24 weeks of training.
All groups increased fat free mass, except the upper body power group, after 24 weeks of training. There were some group differences in percent body fat, but no significant changes over time within any group. Cross sectional areas of the arm increased in all groups (TP=6.6%, TH=15%, UP=11.7%, UH=13.4%). Overall, there was an 11% increase in area from pre to mid training and an increase of ~6% from mid training to post training. For the thigh, only the total body training groups increased their cross sectional area from pre to mid training (TP=4.8%, TH=2.7%) and from mid training to post training (TP=4.8%, TH=4.2%). The cross sectional area of all arm muscles for all training groups was increased over time. The cross sectional area of each of the anterior thigh muscles was increased in the both total body training groups, but only the short head of the biceps femoris. Curiously, the vastus intermedius was increased in both upper body training groups. Squat 1-RM was increased in both total body groups at both test periods while all training groups increased 1-RM bench press performance at all test periods. Jump squat power output at 30% and 60% of 1-RM increased in the TP and TH. Power output during the ballistic bench press was increased significantly from pre to post training in all four training groups. The data for performance were presented in bar graphs making accurate effect size impossible to determine.
This project adds further support for the specificity of training concept in that the upper body training groups had little transfer to the untrained lower body while the total body groups showed improvements for both the upper and lower body measurements. On the strength vs. power question, the authors showed that both were about equally effective at improving strength, power, and cross sectional areas of the muscle groups trained. Of particular interest was the continued improvement in performance by these women throughout the duration of the study demonstrating that women following a well-designed and executed program can continue to show improvements and not reach the early plateau of earlier research.


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