Effects of endurance cycling training on neuromuscular fatigue in healthy active men. Part II: Corticospinal excitability and voluntary activation.

This study investigated the effects of 9-week endurance cycling training on central fatigability and corticomotor excitability of the locomotor muscles. Fourteen healthy participants undertook three incremental fatiguing cycling tests to volitional exhaustion (EXH): (i) before training (PRE), (ii) after training at the same absolute power output as PRE (POSTABS) and (iii) after training at the same percentage of V̇O2max as PRE (POSTREL). At baseline (i.e. before cycling), every 5 min during cycling and immediately at EXH, a neuromuscular evaluation including a series of 5-s knee extensions at 100, 75 and 50% of maximal voluntary knee extension (MVC) was performed. During each contraction, transcranial magnetic and peripheral nerve stimuli were elicited to obtain motor evoked potential (MEP), silent period (SP) and compound muscle action potential (Mmax) and to calculate voluntary activation (VA). The MEP·Mmax-1 ratio recorded from vastus lateralis at 100 and 50% MVC did not show any difference between conditions. At 75% MVC, MEP exhibited significantly lower values in POSTABS and POSTREL compared to PRE at baseline (P = 0.022 and P = 0.011, respectively) as well as at 25% of time to EXH of PRE (P = 0.022) for POSTREL. No adaptations, either at baseline or during cycling, were observed for VA and SPs. In conclusion, endurance training may result in some adaptations in the corticomotor responses when measured at rest or with low level of fatigue, yet these adaptations do not translate into attenuation of central fatigue at a similar cycling workload or at exhaustion.

Effects of endurance training on neuromuscular fatigue in healthy active men. Part I: Strength loss and muscle fatigue.

PURPOSE: The adaptations induced by endurance training on the neuromuscular function remain under investigation and, for methodological reasons, unclear. This study investigates the effects of cycling training on neuromuscular fatigue and its peripheral contribution measured during and immediately after cycling exercise. METHODS: Fourteen healthy men performed a fatigue test before a 9-week cycling program (PRE) and two tests after training: at the same absolute power output as PRE (POSTABS) and based on the post-training maximal aerobic power (POSTREL). Throughout the tests and at exhaustion (EXH), maximal voluntary contraction (MVC) and peripheral fatigue were assessed in the quadriceps muscle by electrical nerve stimulation [single twitch (Pt); high-frequency doublet (Db100) and low-to-high-frequency ratio (Db10:100)]. RESULTS: Time to EXH was longer in POSTABS than PRE (34 ± 5 vs. 27 ± 4 min, P < 0.001), and POSTREL tended to be longer than PRE (30 ± 6 min, P = 0.053). MVC and peripheral fatigue were overall less depressed in POSTABS than PRE at isotime. At EXH, MVC and Db10:100 were similarly reduced in all sessions (-37 to - 42% and - 30 to - 37%, respectively). Db100 tended to be less depressed in POSTABS than PRE (-40 ± 9 vs. - 48 ± 16%, P = 0.050) and in POSTREL than PRE (-39 ± 9%, P = 0.071). Pt decreased similarly in POSTABS and PRE (-52 ± 16 vs. - 54 ± 16%), but POSTREL tended to be less depressed than PRE (-48 ± 14%, P = 0.075). CONCLUSIONS: This study confirms fatigue attenuation at isotime after training. Yet lower or similar fatigue at EXH indicates that, unlike previously suggested, fatigue tolerance may not be upregulated after 9 weeks of cycling training.

Unilateral elbow flexion fatigue modulates corticospinal responsiveness in non-fatigued contralateral biceps brachii.

Exercise-induced fatigue can change motor performance in non-exercised muscles. The objective was to investigate unilateral elbow flexion (EF) fatigue effects on the maximal voluntary force (MVC) and corticospinal excitability of contralateral non-exercised biceps brachii (BB). Transcranial magnetic, transmastoid electrical, and brachial plexus electrical stimulation were used to elicit motor evoked potentials (MEP), cervicomedullary motor evoked potentials (CMEP), and compound muscle action potentials in the contralateral non-exercised BB of 12 participants before and after (i) two bouts of 100-s unilateral EF (fatigue) or (ii) control. Three stimuli were evoked every 1.5 s during a series of 6-s isometric EF at 100%, 50%, and 5% of MVC. The non-exercised EF MVC force, electromyographic activity, and voluntary activation were not significantly different between fatigue and control. Non-exercised BB MEP and CMEP amplitudes during 100% MVCs demonstrated significantly higher (P = 0.03) and lower values (P = 0.01), respectively, after fatigue compared with control. There was no difference between the two conditions for MEP and CMEP amplitudes during 50% and 5% MVCs. Unilateral exercise-induced EF fatigue did not lead to cross-over central fatigue to the contralateral homologous muscle but enhanced the supraspinal responsiveness (MEP/CMEP) of the neural circuitries supplying central commands to non-exercised muscles at higher contraction intensity.

Pain pressure threshold of a muscle tender spot increases following local and non-local rolling massage.

BACKGROUND: The aim of the present study was to determine the acute effect of rolling massage on pressure pain threshold (PPT) in individuals with tender spots in their plantar flexor muscles. METHODS: In a randomized control trial and single blinded study, tender spots were identified in 150 participants' plantar flexor muscles (gastrocnemius or soleus). Then participants were randomly assigned to one of five intervention groups (n = 30): 1) heavy rolling massage on the calf that exhibited the higher tenderness (Ipsi-R), 2) heavy rolling massage on the contralateral calf (Contra-R), 3) light stroking of the skin with roller massager on the calf that exhibited the higher tenderness (Sham), 4) manual massage on the calf that exhibited the higher tenderness (Ipsi-M) and 5) no intervention (Control). PPT was measured at 30 s and up to 15 min post-intervention via a pressure algometer. RESULTS: At 30 s post-intervention, the Ipsi-R (24 %) and Contra-R (21 %) demonstrated higher (p < 0.03) PPT values compared with Control and Sham. During 15 min post-intervention, PPT was higher (p < 0.05) following Ipsi-R (19.2 %), Contra-R (15.9 %) and Ipsi-M (10.9 %) compared with Control. There was no difference between the effects of three deep tissue massages (Ipsi-R, Ipsi-M and Contra-R) on PPT. DISCUSSION: Whereas the increased PPT following ipsilateral massage (Ipsi-R and Ipsi-M) might be attributed to the release of fibrous adhesions; the non-localized effect of rolling massage on the contralateral limb suggests that other mechanisms such as a central pain-modulatory system play a role in mediation of perceived pain following brief tissue massage. CONCLUSION: Overall, rolling massage over a tender spot reduces pain perception. TRIAL REGISTRATION: ClinicalTrials.gov ( NCT02528812 ), August 19(th), 2015.

Pacing strategies during repeated maximal voluntary contractions.

PURPOSE: Pacing strategies have been reported to occur during continuous cyclical exercises. However, currently no studies have examined if pacing takes place during repeated maximal voluntary muscle contractions (MVCs). Accordingly, the purpose of this study was to examine if informing subjects on the number of MVCs they would perform would affect force and root mean squared electromyography (EMG), during similar fatiguing protocols. METHODS: Thirty well-trained male subjects completed three fatiguing protocols in a randomized order. In the control condition participants were informed they would perform 12 MVCs, and then completed all 12. In the unknown condition they were not told how many MVCs they would perform, but were stopped after 12. Lastly, in the deception condition they were initially told they would perform only 6 MVCs, but after the 6 contractions they were asked to perform a few more repetitions and were stopped after 12. RESULTS: Compared to the unknown condition, subjects demonstrated greater forces (p < 0.05, ES = 0.35-1.14, 2-7.5%) and biceps EMG (p < 0.05, ES = 0.6, 6%) in the deception condition during the first six MVCs. Additionally, under all conditions subjects applied greater forces in the last repetition (#12) relative to the previous one (#11) (p < 0.06, ES = 0.36-0.5, 2.8-3.8%). CONCLUSIONS: The anticipation of performing a certain number of MVCs led the subjects to utilize different pacing strategies. The results also question the assumption that subjects followed the instruction to exert maximal effort during repeated MVCs.