Fatigue-related Feedback from Calf Muscles Impairs Knee Extensor Voluntary Activation

Abstract

Introduction Fatigue-related group III/IV muscle afferent firing from agonist, antagonist or distal muscles impairs the ability to drive the elbow flexors maximally, that is, reduces voluntary activation. In the lower limb, the effect of feedback from distal muscles on the proximal knee extensors is unknown. Here, we test whether maintained group III/IV afferent feedback from the plantarflexor muscles reduces voluntary activation of the knee extensors. Methods On 2 d, voluntary activation of the knee extensors during maximal voluntary contractions (MVCs) was assessed in 12 participants before and after a 3-min fatiguing task of the plantarflexors. On 1 d, an inflatable cuff around the calf occluded blood flow for 2 min immediately postexercise (cuff day). The other day had no occlusion (no-cuff day). Supramaximal stimulation of the femoral nerve elicited superimposed twitches during MVC of the knee extensors and resting twitches 2 to 3 s after relaxation. Pain (0–10 point scale) was reported throughout. Results In the 2 min after the 3-min fatiguing plantarflexor task, voluntary activation was 5.3% (SD, 7%) lower on the cuff day than on the no-cuff day (P = 0.045), and MVC force was reduced by 13% (SD, 16%) (P = 0.021). The resting twitch was similar on both days (P = 0.98). Pain rated 4.9 points higher with the cuff inflated (P = 0.001). Conclusions Maintained group III/IV afferent feedback from the fatigued plantarflexor muscles reduced maximal force and voluntary activation of the unfatigued knee extensors, suggesting that afferents from the calf act centrally to inhibit the ability to drive the motoneurones of the knee extensors.

Pharmacological Blockade of Muscle Afferents and Perception of Effort: A Systematic Review with Meta-analysis

“…An interesting approach could consist of increasing feedback from group III-IV muscle afferents concomitantly of the presence of the perception of effort. This is possible for example with the use of intramuscular metabolites or saline injection [e.g., 127,128,129] or cuff-induced muscle ischemia [e.g., 130,131,132]. Due to the overall inhibitory effect of group III/IV muscle afferents on the corticospinal pathway and the generation of the motor command, thus contributing to the development of neuromuscular fatigue [38,39], we would expect an increase in the perception of effort.…”

The corticomuscular response to experimental pain via blood flow occlusion when applied to the ipsilateral and contralateral leg during an isometric force task

“…While BFO paradigms are typically implemented by occluding the exercising musculature (i.e., ipsilateral), there is growing interest in exploring the perceptual and neuromuscular responses to BFO of nonexercising (typically contralateral) musculature during exercise (Finn et al., 2020). This is useful because this approach can stimulate group III–IV muscle afferents without altering the exercising muscle's metabolic status.…”

The effect of hypertonic saline evoked muscle pain on neurophysiological changes and exercise performance in the contralateral limb

“…When ischaemia was induced on the left leg to gradually increase muscle pain, a 21% reduction in single limb cycling time to task failure (TTF) was seen in the right leg, which was coupled with lesser end-exercise reduction in maximum force and potentiated twitch force compared to no prior fatigue. Additionally, reductions in voluntary activation of non-local muscles have been found following a fatiguing protocol and subsequent maintenance of group III/IV afferent firing (and pain) through ischemia (Kennedy et al 2013(Kennedy et al , 2014(Kennedy et al , 2015Finn et al 2020). Therefore, it is unclear how muscle pain may act at a non-local level to impact neuromuscular fatigue and endurance performance.…”