Fiber type composition of the vastus lateralis muscle of young men and women.

This study presents data collected over the past 10 years on the muscle fiber type composition of the vastus lateralis muscle of young men and women. Biopsies were taken from the vastus lateralis muscle of 55 women (21.2+/-2.2 yr) and 95 men (21.5+/-2.4 yr) who had volunteered to participate in various research projects. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were classified using mATPase histochemistry, and cross-sectional area was measured for the major fiber types (I, IIA, and IIB). Myosin heavy chain (MHC) content was determined electrophoretically on all of the samples from the men and on 26 samples from the women. With the exception of fiber Type IC, no significant differences were found between men and women for muscle fiber type distribution. The vastus lateralis muscle of both the men and women contained approximately 41% I, 1% IC, 1% IIC, 31% IIA, 6% IIAB, and 20% IIB. However, the cross-sectional area of all three major fiber types was larger for the men compared to the women. In addition, the Type IIA fibers were the largest for the men, whereas the Type I fibers tended to be the largest for the women. Therefore, gender differences were found with regard to the area occupied by each specific fiber type: IIA>I>IIB for the men and I>IIA>IIB for the women. These data establish normative values for the mATPase-based fiber type distribution and sizes in untrained young men and women.

The effectiveness of 0.5-lb increments in progressive resistance exercise.

A traditional progressive resistance exercise program consists of increasing the number of repetitions at a constant load until exceeding an established repetition range. Subsequently, the load is increased by 1.1 kg (2.5 lb) or more, and the lifter works at the new load until again exceeding the repetition range. This investigation examines the use of small incremental loads for 2 upper-body exercises (bench press and triceps press). Subjects were randomly assigned to traditional (TRAD) progressive resistance exercise (5 women, 5 men) and small increment (SI) progressive resistance exercise (5 women, 4 men) groups. Initially, both groups trained for 8 weeks using TRAD progressive resistance exercise. Subjects who achieved 7 repetitions on the final set of an exercise increased the load for the next session by 2.2 (bench press) or 1.1 kg (triceps press). Following the initial 8-week training period, the TRAD group continued for another 8 weeks following the same protocol, whereas the SI group trained for an additional 8 weeks, increasing the load by 0.22 kg (0.5 lb) when completing 7 or 8 repetitions and 0.44 kg (1 lb) when achieving 9 or more repetitions. All groups, except TRAD women, made significant increases in 1 repetition maximum (1RM) for the bench press. Both TRAD men and SI men significantly increased 1RM triceps press. Groups that did not significantly increase 1RM, in either the bench press or triceps press, demonstrated similar trends. For TRAD men and SI men, the number of repetitions to failure for the bench press at 60% 1RM decreased after training. Both regimens proved effective for increasing strength throughout 8 weeks. In conclusion, SI progressive resistance exercise appears to be as effective as TRAD progressive resistance exercise for increasing strength during 8 weeks in short-term pretrained college-aged men and women. However, preliminary data suggest that the TRAD progressive resistance exercise program might be a more effective method of increasing resistance during an extended period.

In vivo measurement of fascicle length and pennation angle of the human biceps femoris muscle.

The purpose of this investigation was to measure in vivo fascicle length (L(fas)) and pennation angle (PA) of the long head of the biceps femoris muscle (BF(lh) m.) at different hip and knee angles while the muscle was relaxed using ultrasonography (US). Data were collected from 18 healthy females (23.0 +/- 1.8 years). To validate the measurements of the L(fas) and PA, the US measurements on cadavers (n = 5), embalmed with the hip and knee in anatomical position, were compared to actual fiber lengths and PA from the dissected muscles. US images from volunteer subjects were recorded when the hip joint was positioned at 0 degrees, 45 degrees and 90 degrees of hip flexion, and at each hip position, the knee joint was placed at 0 degrees, 45 degrees and 90 degrees from full extension. The images were digitized to measure L(fas) and PA. Results showed no significant differences between US and direct measurements of the L(fas) and PA on the cadaver BF(lh) m. (p > 0.05). L(fas) and PA changed significantly between the different hip and knee positions in volunteer subjects (p < 0.05). Changes in the L(fas) and PA are more sensitive to changes in hip position with the knee position constant than to changes in knee position with the hip position constant. This difference may be related to the larger muscle moment arm at the hip resulting in greater excursion of the muscle with changing hip position. Based on the changes in L(fas) with changing joint positions, BF(lh) sarcomere length was estimated to occupy a portion of the ascending limb, the plateau and descending limb of the length-tension relationship over the range of motion studied. US scanning is valid and reliable for measuring L(fas) and PA of the BF(lh) m. An understanding of the dynamic nature of muscle architecture will assist in determining effective and efficient clinical evaluation and rehabilitation techniques.

Skeletal muscle adaptations in elastic resistance-trained young men and women.

Skeletal muscle adaptations (fiber-type composition, cross-sectional area, myosin heavy chain (MHC) content, and capillarity) were assessed in the vastus lateralis muscle of young men and women after 8 weeks of training with the Sportcord, an elastic resistance device. Ten men [mean (SD) age 20 (1.1) years] and 13 women [20 (1.2) years] performed two sets each to failure of single leg squats and leg extensions at approximately 50 repetitions x min(-1). Biopsy samples were taken from the right vastus lateralis muscle before and after training. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were classified using myofibrillar ATPase histochemistry. Training with the Sportcord caused a small, but significant, increase in one-repetition maximum using free weights and a large increase in repetitions to failure. In addition, elastic resistance training caused an increase in the percentage of fibers classified as type IIAB for both men and women, and a decrease in the percentage of type IIB fibers in the men. MHC analysis supported these findings (a significant increase in the percentage of MHCIIa for the men). The cross-sectional areas ofboth the type I and IIAB + IIB fibers increased after training for the men, whereas no area changes were found for the women. The capillary:fiber ratio and capillary contacts per fiber type increased significantly for the men, and similar trends were noted for the women. Capillary density did not change in either the men or the women. These data suggest minor changes in fiber type composition (IIB-->IIAB), fiber size, and capillarization following short-term training with elastic resistance. Although muscular changes did occur using the Sportcord, the extent of these changes was less than those reported previously for short-term resistance-training programs using free weights.