Energy metabolism during repeated sets of leg press exercise leading to failure or not

Abstract

This investigation examined the influence of the number of repetitions per set on power output and muscle metabolism during leg press exercise. Six trained men (age 34 ± 6 yr) randomly performed either 5 sets of 10 repetitions (10REP), or 10 sets of 5 repetitions (5REP) of bilateral leg press exercise, with the same initial load and rest intervals between sets. Muscle biopsies (vastus lateralis) were taken before the first set, and after the first and the final sets. Compared with 5REP, 10REP resulted in a markedly greater decrease (P<0.05) of the power output, muscle PCr and ATP content, and markedly higher (P<0.05) levels of muscle lactate and IMP. Significant correlations (P<0.01) were observed between changes in muscle PCr and muscle lactate (R(2) = 0.46), between changes in muscle PCr and IMP (R(2) = 0.44) as well as between changes in power output and changes in muscle ATP (R(2) = 0.59) and lactate (R(2) = 0.64) levels. Reducing the number of repetitions per set by 50% causes a lower disruption to the energy balance in the muscle. The correlations suggest that the changes in PCr and muscle lactate mainly occur simultaneously during exercise, whereas IMP only accumulates when PCr levels are low. The decrease in ATP stores may contribute to fatigue.

Figure 1. Peak power output profiles (average for n = 6 subjects) for each exercise during the two experimental conditions: when exercise was 5 sets of 10 repetitions to failure (10REP; open circles), and when exercise was 10 sets of 5 repetitions not to failure (5REP; filled circles).

Boxes represent mean of the peak power output throughout 50 repetitions for 10REP and 5REP. *significant difference (P<0.05) between 10REP and 5REP (pooled from 5 to 5 repetitions). Values are means ± SD.

Figure 2. Individual relationship between muscle lactate concentrations and PCr concentrations (expressed in percent of initial value) (2A) and between PCr decreases (expressed in percent of initial value) and muscle IMP concentrations (2B), during 10REP (open circles), and 5REP (filled circles).

Figure 3. Individual relationships between the relative average peak power output changes (expressed in percent of initial value) between the first and the last two repetitions, and ATP decreases (expressed in percent of initial value), during 10REP exercise (open circles), and 5REP exercise (filled circles).

Figure 4. Individual relationships between the relative average peak power output changes (expressed in percent of initial value) between the first and the last two repetitions of the first set and between the first and last two repetitions of the exercise, and muscle lactate concentrations, during 10REP (open circles), and 5REP (filled circles).