Spinal contribution to neuromuscular recovery differs between elbow-flexor and knee-extensor muscles after a maximal sustained fatiguing task

Abstract

Data from studies of elbow-flexor (EF) or knee-extensor (KE) muscles suggest that a fatigue-related decrease in motoneuron excitability only occurs in EF. It is unknown how motoneuron excitability changes after sustained fatiguing maximal voluntary isometric contractions (MVICs) in EF and KE in the same participants. In two sessions, eight healthy men performed a 2-min MVIC of EF or KE to induce fatigue with brief MVICs before and six times after the 2-min MVIC. Electromyographic responses elicited by corticospinal tract stimulation at the transmastoid [cervicomedullary motor-evoked potential (CMEP)] or thoracic [thoracic motor-evoked potential (TMEP)] level were recorded from EF and KE, respectively. To account for muscle excitability, CMEPs and TMEPs were normalized to maximal M-wave (Mmax) elicited by peripheral nerve stimulation during each brief MVIC. Immediately after the 2-min MVIC, biceps brachii and brachioradialis CMEP/Mmax were 88% (SD 11%) (P = 0.026) and 87% (SD 12%) (P = 0.029) of pre-MVIC values, respectively, and remained lower than PRE after 5 s of recovery [91% (SD 8%), P = 0.036 and 87% (SD 13%), P = 0.046, respectively]. No subsequent time points differed from PRE (all P ³ 0.253). TMEP/Mmax for rectus femoris and vastus lateralis were not different from PRE at any time during the recovery period (all P > 0.050). A different recovery pattern in motoneuron excitability occurred in EF as it recovered by 60 s whereas KE motoneurons were unaffected by the fatiguing task. The present findings may contribute to better understand muscle-specific neurophysiological differences in spinal excitability.

Downhill running affects the late but not the early phase of the rate of force development

“…First, our POST measurements were collected after 90 s of recovery. As recovery kinetics at the level of the central nervous system is rapid (Kennedy et al 2016 ; Mira et al 2017 ; Vernillo et al 2018 ; Krüger et al 2019 ; Koral et al 2020 ; Vernillo et al 2020b ; Ducrocq et al 2021 ), we cannot rule out that the capacity to deliver maximal discharge frequency and incidence of doublet discharge during fast contractions (i.e., the neural factors influencing RFD) has been underestimated in the present study. Second, RFD contractions also depend on the ability of the individual to perform impulsive contractions.…”

Performance fatigability and recovery after dynamic multi-joint maximal exercise in elbow flexors versus knee extensors

“…Thus, to understand beyond immediately post-exercise, MVIC force recovery must be considered. Previous studies have shown that the magnitude and mechanisms of recovery after fatiguing exercise are related to the characteristics of the preceding exercise bout (12) and may be different between muscle groups (4,9,16). For example, Vernillo et al (16) showed that after a sustained 2-min MVIC, MVIC force gradually recovered and returned to baseline values for both EF and KE within 4 min of recovery; whereas Senefeld et al (9) reported that EF MVIC force loss was ~15% lower than KE MVIC force 10 min after completing 90 submaximal isotonic contractions at maximal voluntary shortening velocity.…”