Influence of fascicle strain and corticospinal excitability during eccentric contractions on force loss

Abstract

New Findings What is the central question of this study?Do neural and/or mechanical factors determine the extent of muscle damage induced by eccentric contractions? What is the main finding and its importance?The extent of muscle damage induced by eccentric contractions is related to both mechanical strain and corticospinal excitability measured at long muscle lengths during eccentric contractions. Abstract In this study, we investigated whether the mechanical and neural characteristics of maximal voluntary eccentric contractions would determine the extent of change in postexercise maximal voluntary isometric contraction (MVC) torque and muscle soreness. Eleven men performed 10 sets of 15 isokinetic (45 deg s−1) maximal voluntary eccentric knee extensions. Knee‐extension torque and vastus lateralis fascicle length were assessed at sets 1, 5 and 9. Vastus lateralis motor evoked potential, maximal M wave (MEP/M) and the cortical silent period (CSP) were measured at 75 and 100 deg of knee flexion (0 deg = full extension) during contractions and were normalized to MEP/M (MEP/Mecc/iso) and CSP (CSPecc/iso) recorded during isometric MVC at each angle. The MVC torque and muscle soreness of the knee extensors were assessed before, 24, 48 and 96 h after the eccentric contractions. The extent of relative decrease in MVC torque at 24 h postexercise (r2 = 0.38) and peak muscle soreness (r2 = 0.69) were correlated (P < 0.05) with MEP/Mecc/iso measured at 100 deg, but not at 75 deg. The average torque on the descending limb of the torque–angle relationship (r2 = 0.16), fascicle elongation (r2 = 0.18) and CSPecc/iso at both 75 (r2 = 0.00) and 100 deg (r2 = 0.02) were not significantly correlated with the relative decrease in MVC torque. The relative decrease in MVC torque was best predicted by a combination of mean torque on the descending limb, fascicle elongation and MEP/Mecc/iso (R2 = 0.93). It is concluded that the extent of muscle damage based on the reduction in MVC torque is determined by mechanical strain and corticospinal excitability at long muscle lengths during maximal voluntary eccentric contractions.

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

“…This result is in accordance with the alteration of neuromuscular transmission after eccentric exerciseinduced muscle damage (Hedayatpour and Falla 2012) and the disturbance in post-synaptic regulation of acetylcholine as a result of neuromuscular junction remodeling at the injured sites (Warren et al 1999). In addition, a decreased voluntary activation has been reported (Fouré et al 2014) which can be related to the corticospinal contribution in the decreased MVC force observed following damaging eccentric contractions (Doguet et al 2019). Based on the T 2 changes reported in the present study, muscle alterations were highlighted at long muscle length in comparison to short muscle length condition.…”

“…It would have been of interest to assess the strain on active fascicles but also on passive structures such as series elastic components during the NMES-isometric contractions throughout the exercise. The impact of the fascicle/passive structures strain at short and long muscle lengths on the extent of muscle T 2 increase and MVC force decrease could have been assessed as reported recently during voluntary eccentric contractions (Guilhem et al 2016;Doguet et al 2019).…”

“…Similar NMES sessions were randomly performed either with the knee flexed at 100° corresponding to a long muscle-tendon length (hereafter referred to as long muscle length) and with the contralateral knee flexed at 50° corresponding to a short muscle-tendon length (hereafter referred to as short muscle length). Link between knee joint angle and muscle fascicle length was performed on the basis of ultrasound imaging measurements on the vastus lateralis during eccentric contractions with a mean fascicle length of 85 mm and 100 mm at a knee flexion angle of 40° and 100°, respectively (Doguet et al 2019). Considering that VL muscle slack length was assessed for a knee flexion angle of 24° [range 16°-30°] (Stubbs et al 2018), we assume that the two testing positions were beyond the VL slack length (Stubbs et al 2018;Xu et al 2018).…”

“…Similarly, eccentric exercise involving high force generation and a high number of repetitions can cause large muscle fibre structural alterations (Lieber and Friden 1993;Paulsen et al 2012). Using real-time ultrasound imaging, it has been reported that the amount of fascicle length changes during maximal voluntary eccentric contractions and then the level of negative work imposed by the exercise is highly involved in the subsequent MVC force loss (Guilhem et al 2016;Doguet et al 2019). Muscle damage has also been reported as a result of intense voluntary isometric contractions (> 60% MVC) performed at long muscle length (Allen et al 2018) even if muscle force and length change were lower than what could be generated during maximal voluntary eccentric contractions.…”

Effects of wrist position on eccentric exercise‐induced muscle damage of the elbow flexors

“…Guilhem et al 14 found that the muscle fascicle lengthening during 10 sets of 30 maximal eccentric plantar flexor contractions was correlated with the magnitude of the force decrease at 2 days post‐exercise (assumed to reflect the extent of muscle damage), indicating that muscle lengthening critically influences the damage response. More recently, Doguet et al 18 reported that the magnitude of decrease in maximal voluntary knee extensor torque was related to both mechanical (ie, torque production and fascicle elongation) and neural (ie, corticospinal excitability) factors present at long muscle lengths during maximal voluntary eccentric contractions. However, it cannot be determined from these data whether the initial or average muscle length also influences this response.…”