The Effect of Elevated Muscle Pain on Neuromuscular Fatigue during Exercise

Abstract

Purpose: Muscle pain can impair exercise performance but the mechanisms for this are unknown. This study examined the effects of muscle pain on neuromuscular fatigue during an endurance task. Methods: On separate visits, twelve participants completed an isometric time to task failure (TTF) of the right knee extensors at ~20% of maximum force following an intramuscular injection of isotonic saline (CTRL) or hypertonic saline (HYP) into the vastus lateralis. Measures of neuromuscular fatigue were taken before, during and after the TTF using transcranial magnetic stimulation (TMS) and peripheral nerve stimulation (PNS). Results: The mean pain intensity was 57 ± 10 in HYP compared to 38 ± 18 in CTRL (P < 0.001). TTF was reduced in HYP (4.36 ± 0.88 min) compared to CTRL (5.20 ± 0.39 min) (P = 0.003). Maximum voluntary force was 12 % lower at minute 1 (P = 0.003) and 11 % lower at minute 2 in HYP (P = 0.013) compared to CTRL. Voluntary activation was 4 % lower at minute 1 in HYP compared to CTRL (P = 0.006) but not at any other time point (all P > 0.05). The TMS silent period was 9 % longer at 100 s during the TTF in HYP compared to CTRL (P = 0.026). Conclusion: Muscle pain reduces exercise performance through the excacerbation of neuromuscular fatigue that is central in origin. This appears to be from inhibitory feedback from group III/IV nociceptors which acts to reduce central motor output.

The impact of postexercise blood flow restriction on local muscle endurance of a remote limb

“…We feel that part of the small difference in discomfort was related to the rather long 5–10‐day duration between experimental trials whereby individuals may have had a difficult time recollecting the feeling of the prior trial when providing their discomfort rating. Nonetheless, our difference in discomfort ratings was similar to what has been reported previously (pain ratings of 57 vs. 38 in experimental and control) and shown to have an effect when applied to the specific muscle being tested (Norbury et al, 2021). Another limitation exists in that we did not remeasure the arterial occlusion pressure on the day of the experimental visit to keep the participants blinded to their trial visit.…”

“…Nonetheless, our difference in discomfort ratings was similar to what has been reported previously (pain ratings of 57 vs. 38 in experimental and control) and shown to have an effect when applied to the specific muscle being tested (Norbury et al, 2021). Another limitation exists in that we did not remeasure the arterial occlusion pressure on the day of the experimental visit to keep the participants blinded to their trial visit.…”

“…Studies demonstrating that the injection of hypertonic saline limits both maximal force and endurance capacity would suggest these group III/IV afferents; however, do induce a localized effect on the muscle being tested (Norbury et al, 2021; Smith et al, 2020). Other studies have demonstrated that these injections can also reduce the excitability of synergistic muscles that are involved in the task (Ciubotariu et al, 2004).…”

“…Common methods used to activate group III/IV afferents involve inducing localized pain via ischaemia, hypertonic saline injections, or the use of systemic chemical injections (Staahl & Drewes, 2004). These methods can be combined with exercise to either inhibit or exacerbate the activation of group III/IV afferents that are already being activated by exercise itself (Ciubotariu et al, 2004; Norbury et al, 2021; Smith et al, 2020). For example, the injection of hypertonic saline into the quadriceps (Norbury et al, 2021; Smith et al, 2020) or calf muscles (Ciubotariu et al, 2004) has been shown to exacerbate sensations of pain and reduce time to task failure when administered during sustained isometric contractions.…”

“…These methods can be combined with exercise to either inhibit or exacerbate the activation of group III/IV afferents that are already being activated by exercise itself (Ciubotariu et al, 2004; Norbury et al, 2021; Smith et al, 2020). For example, the injection of hypertonic saline into the quadriceps (Norbury et al, 2021; Smith et al, 2020) or calf muscles (Ciubotariu et al, 2004) has been shown to exacerbate sensations of pain and reduce time to task failure when administered during sustained isometric contractions. Furthermore, ischaemia applied postexercise may induce sensations of discomfort and limit the strength of the exercised and ipsilateral muscles but not contralateral muscles (Kennedy et al, 2013, 2015; Pethick et al, 2018).…”