Protective Effect Conferred by Isometric Preconditioning Against Slow- and Fast-Velocity Eccentric Exercise-Induced Muscle Damage

Abstract

We investigated if the same isometric preconditioning protocol (IPP) attenuates the magnitude of muscle damage induced by different maximal eccentric exercise protocols in the elbow flexors. Sixty-four untrained men were assigned to either two experimental or two control groups. Participants in the experimental groups performed an IPP prior to either slow (60°·s^-1 - ISO + ECC-S) or fast (180°·s^-1 - ISO + ECC-F) maximal eccentric contractions (MaxECC). Subjects in the control groups performed slow (ECC-S) or fast (ECC-F) MaxECC without IPP. Maximal isokinetic concentric torque (MVC), muscle soreness (SOR), and muscle thickness (MT) were assessed before, immediately after, and 1-4 days following the MaxECC. Significant (p < 0.05) group vs. time interactions were found for MVC (F = 4,517), SOR (F = 6,318), and MT (F = 1,863). The ECC-S group presented faster (p < 0.05) recovery of MVC and MT and less (p < 0.05) SOR at 96 h post-MaxECC compared with ECC-F group. No significant differences in MVC and MT were found between ECC-S and ECC-F groups following MaxECC. The ISO + ECC-S group showed faster (p < 0.05) recovery of MVC and SOR compared to the ECC-S group. No significant differences were evident between ISO + ECC-S and ECC-S in any variable. The ISO + ECC-F group showed faster (p < 0.05) recovery of all assessed variables compared with the ECC-F group. MVC was greater (p < 0.05) at 48-72 h, and SOR was less (p < 0.05) at 48-96 h in the ISO + ECC-F compared to the ECC-F group. No significant differences were evident between ISO + ECC-S and ISO + ECC-F for any variable. These results show that the IPP accelerated recovery of MVC and SOR for the slow-eccentric exercise condition and attenuated strength loss and SOR in addition to faster recovery of all assessed variables for the fast-eccentric exercise condition. Therefore, the IPP can be used as a strategy to attenuate and accelerate recovery of muscle damage induced by different-velocity eccentric exercises, resulting in greater protection against muscle damage induced by faster velocity.

Keywords: delayed-onset muscle soreness; eccentric exercise; index of protection; muscle damage; repeated bout effect; strength loss.

Figure 1

Changes (mean ± SD) in isometric peak torque over the repetitions during isometric preconditioning protocol for the experimental groups (ISO + ECC-S and ISO + ECC-F). No significant differences over repetitions were found between groups (p > 0.05).

Figure 2

Changes (mean ± SD) in average peak torque over the sets during the slow-eccentric exercise (ECC-S and ISO + ECC-S, two sets of maximal slow-eccentric contractions) and fast-eccentric exercise (ECC-F and ISO + ECC-F, six sets of maximal fast-eccentric contractions). (*) p < 0.05 for ECC-F vs. ISO + ECC-S, (a) p < 0.05 from the first set for ECC-S and ISO + ECC-S, (b) p < 0.05 from the first set for ECC-F and ISO + ECC-F, (c) p < 0.05 from the previous set for ECC-F, and (d) p < 0.05 from the previous set for ISO + ECC-F.

Figure 3

Average total work (mean ± SD) of slow- (ECC-S and ISO + ECC-S) and fast-eccentric (ECC-F and ISO + ECC-F) exercises. (*) p < 0.05 vs. ECC-S and ISO + ECC-S.

Figure 4

Normalized changes (mean ± SD) in maximal voluntary concentric contraction peak torque before (Pre), immediately after (Post) and 24–96 h after maximal eccentric exercise. (*) p < 0.05 for ECC-F vs. ISO + ECC-F, (a) p < 0.05 vs. Pre for ECC-S, (b) p < 0.05 vs. Pre for ISO + ECC-S, (c) p < 0.05 vs. Pre for ECC-F, and (d) p < 0.05 vs. Pre for ISO + ECC-F.

Figure 5

Absolute changes (mean ± SD) in SOR before (Pre) and 24–96 h after maximal eccentric exercise. (*) p < 0.05 for ECC-F vs. ISO + ECC-F, (†) p < 0.05 for ECC-S vs. ECC-F, (a) p < 0.05 vs. Pre for ECC-S, (b) p < 0.05 vs. Pre for ISO + ECC-S, (c) p < 0.05 vs. Pre for ECC-F, and (d) p < 0.05 vs. Pre for ISO + ECC-F.

Figure 6

Normalized changes (mean ± SD) in MT before (Pre), immediately after (Post), and 24–96 h after maximal eccentric exercise. (a) p < 0.05 vs. Pre for ECC-S, (b) p < 0.05 vs. Pre for ISO + ECC-S, (c) p < 0.05 vs. Pre for ECC-F, and (d) p < 0.05 vs. Pre for ISO + ECC-F.

Figure 7

Index of protection of isometric preconditioning on the two conditions of muscle damage. Indexes of protection are expressed as percentage (%) for groups that performed slow-eccentric exercise (SEE) or fast-eccentric exercise (FEE) for maximal voluntary concentric contraction (MVC), muscle soreness (SOR), and muscle thickness (MT) variables, based on the following equation: (percentage change in the variable for the control group − percentage change in the variable for the experimental group)/percentage change in the variable for the control group × 100. The greater the percentage value, the greater the protective effect induced by isometric preconditioning.