Muscle alterations induced by electrostimulation are lower at short quadriceps femoris length

Abstract

Purpose This study aimed at determining through MRI investigations, force and soreness assessments whether the modulation of muscle length is a relevant strategy for minimising neuromuscular electrical stimulation (NMES)-induced muscle damage in young healthy participants. Methods Comparison of 2 NMES sessions (40 isometric electrically-evoked contractions of the knee extensors) was randomly performed on 1 knee flexed at 50° (short muscle length) and the contralateral at 100° (long muscle length) in a single group of healthy participants. Indirect markers of muscle damage including changes in maximal voluntary isometric contraction (MVC) force, muscle volume and transverse relaxation time (T 2 ) were measured before, 2 days (D2), 4 days (D4) and 7 days (D7) after the NMES sessions in each limb of the ten participants. Results Although stimulation intensity was similar during the NMES session on both limbs, significantly lower force production was recorded at long muscle length (peak at 30 ± 5% MVC force) as compared to short muscle length (peak at 61 ± 12% MVC force). In the following days, MVC force at long muscle length was decreased from D2 to D7, whereas no significant change occurred at short muscle length. Increases in muscle volume and T 2 were found at each time point in stimulated muscles at long muscle length, whereas no change was found at short muscle length. Conclusion For the same stimulation intensity, NMES-induced isometric contractions generate higher knee extension force output and result in lower muscle tissues alterations that could be related to a lower intramuscular shear strain when exercise is performed at short muscle length.

Skeletal Muscle Damage Produced by Electrically Evoked Muscle Contractions

“…In addition, a long-lasting T 2 increase was reported in the VL muscle 21 d after the NMES session (10). In agreement with the minor changes in MVC force, such MRI parameters were not significantly affected when NMES was performed at short muscle lengths (28).…”

“…NMES-induced muscle damage was often assessed from indirect markers, such as decreased MVC force, blood sampling parameters (e.g., creatine kinase [CK]) activity) and delayed-onset muscle soreness (10,22,23,(28)(29)(30)(31)(32)(33).…”

“…Therefore, the transverse strain could be involved in specific damage of costameres within deep muscle fibers. This phenomenon could be further exacerbated at long muscle lengths when the passive tension in the muscle-tendon unit is increased, as illustrated by the lack of damage in stimulated muscles at short muscle lengths (28).…”

“…1) actually induced severe damage (10,21), whereas no or minor changes in force were reported after NMES at short muscle lengths (i.e., defined as a joint position lower than 50% RoM max ) (Fig. 1) (28). However, our understanding of the physiological and mechanical processes involved in the severe damaging effects of NMES-evoked submaximal isometric contractions remains unclear.…”

“…The joint angle used during the NMES session (θ NMES ) was normalized to the RoM max as %RoM max = ((θ NMES − θ min )/RoM max  100). For instance, when θ NMES = 50°for the knee extensors (28), %RoM max = 35.7% (i.e., ((50°− 0°)/ 140°Â 100); when θ NMES = 160°for the elbow flexors (23), %RoM max = 85.7% (i.e., (160°− 40°)/140°Â 100). Experimental conditions (A-E), changes in maximal voluntary isometric contraction (MVC) force (F), evoked force during the NMES session (G), changes in CK activity (H), and the delayed-onset muscle soreness assessed from the visual analog scale (VAS) (I) were reported.…”