Matthew P. Harber

Skeletal muscle and hormonal adaptations to circuit weight training in untrained men.

Twelve men either performed 10 weeks of timed circuit weight training 3 days week−1 (CWT; n=8; X±SE; age=23.6±1.8 years), or were part of a sedentary control group (n=4; age=20.5±1.0 years). Significance was P<0.05 for all analyses. The CWT program significantly increased 1 repetition maximum (1 RM) strength for nine of 10 exercises (15–42%). Although no body composition measure significantly changed for the CWT group, low‐to‐moderate effect sizes were evident for body weight, lean body mass, and relative fat. CWT did not alter percent fiber type, but did increase cross‐sectional areas for type IIA fibers (μm2; pre=5988±323, post=7259±669). Relative (%) myosin heavy‐chain (MHC) expression increased for MHC IIa (pre=42.5±2.7, post=50.1±2.6), and decreased for MHC IIb (pre=21.8±2.8, post=15.4±2.4) for the CWT group. Serum testosterone, cortisol, and the testosterone/cortisol ratio did not change at any time for the CWT group. None of the measured variables changed for the control group. These data indicate that for untrained subjects, CWT of the type used resulted in improved muscular strength and a tendency toward increased lean mass. Compared with other types of weight training, fewer adaptations of the muscle fibers were evident. This is likely due in part to the relatively low loads used with this type of resistance exercise.

Myocellular Basis for Tapering in Competitive Distance Runners

The purpose of this study was to examine the effects of a 3-wk taper on the physiology of competitive distance runners. We studied seven collegiate distance runners (20+/-1 yr, 66+/-1 kg) before and after a 3-wk taper. The primary measures included 8-km cross-country race performance, gastrocnemius single muscle fiber size and function (peak force, shortening velocity, and power), baseline and exercise-induced gene expression 4 h after a standardized 8-km run, citrate synthase activity, and maximal and submaximal cardiovascular physiology (oxygen consumption, ventilation, heart rate, and respiratory exchange ratio). Race performance improved by 3% following taper (P<0.05). Myosin heavy chain (MHC) IIa fiber diameter (+7%, P<0.05), peak force (+11%, P=0.06), and absolute power (+9%, P<0.05) increased following taper. In addition to the MHC IIa adaptations, taper elicited a distinct postexercise gene response. Specifically, the induction of MuRF-1 was attenuated following taper, whereas MRF4, HSP 72, and MT-2A displayed an exaggerated response (P<0.05). No changes were observed in MHC I size or function, baseline gene expression, citrate synthase activity, or cardiovascular function. Our findings show that tapered training in competitive runners promoted MHC IIa fiber remodeling and an altered transcriptional response following the same exercise perturbation, with no adverse affects on aerobic fitness. Together, these results provide a myocellular basis for distance runners to taper in preparation for peak performance.