Introduction Neuromuscular fatigue is defined as a reversible, time-dependent decline in the maximal force-generating capacity of a muscle originating at both central and/or peripheral levels. Previous data inferred from sustained isometric contractions suggest that elbow flexors (EF) and knee extensors (KE) present different magnitudes of global, central and peripheral fatigue. During dynamic exercises, contribution of these components may vary according to different muscle perturbations coming from lower motor-unit discharge rate, even at high intensity, and a recovery period among contractions. The aim of this study was to evaluate the contribution of central and peripheral factors to neuromuscular fatigue in EF vs. KE after arm-cranking and cycling exercises. Methods Eleven physically active men (age: 23.8±2.4ys) participated in the study and performed in a pseudo-randomised and counterbalanced order two incremental exercises (INCR) until exhaustion on either a cycle- (CYCLE) or an arm- (ARM) ergometer. During INCR, breath-by-breath pulmonary oxygen uptake (V’O2) and heart rate (HR) were evaluated. Neuromuscular function of KE (quadriceps muscle) and EF (biceps brachii) was assessed before (PRE), 2 min (POST) and 20 min (POST20) after INCR cessation during maximal voluntary contractions and in relaxed muscles. Global fatigue was assessed from maximal isometric force (MVF) during maximal voluntary contractions. To quantify central fatigue, voluntary activation (VA) levels were determined by the adapted twitch interpolation technique. To identify peripheral fatigue, high- (100 Hz, Db100), low- (10 Hz, Db10) frequency doublets and single twitches (Tw) were delivered to the relaxed muscle. The presence of low-frequency fatigue (LFF) was evaluated from the change in the Db10:Db100 ratio. Surface electromyography sensors were placed in correspondence of the vastus medialis, vastus lateralis, and rectus femoris or biceps brachii. Results At the end of INCR, time to exhaustion was not different between CYCLE and ARM (802±93 vs. 886±164 s, p<0.01). V’O2 was higher in CYCLE than ARM (3.41±0.50 vs. 2.47±0.60 L*min-1, p<0.001). At POST, MVF decreased after both CYCLE (21±13%) and ARM (26±7%). At POST20, MVF recovered to resting values in KE ( ̴4% of PRE) while it partially recovered in EF ( ̴17% of PRE). VA was not different in all conditions for both KE and EF. At POST, Db100 (-30%) and LFF (-28%) were significantly reduced in both KE and EF (p<0.01). At POST20, Db100 partially recovered ( ̴15% of PRE) in both KE and EF while LFF did not significantly recovered in EF. Conclusion The present results suggest that neuromuscular fatigue of knee extensors and elbow flexors after incremental exercise mainly originates at peripheral level, with peripheral fatigue still presents in elbow flexors after 20 min of recovery. Thus, recovery from dynamic exercises involving lower or upper limbs should take into account the higher contribution of peripheral factors on muscle fatigue in elbow flexors.

Neuromuscular fatigue in elbow flexors vs. knee extensors after arm-cranking and cycling exercises / M. Colosio, L. Rasica, G. Baldassarre, G. Vernillo, M. Marzorati, S. Porcelli. ((Intervento presentato al 24. convegno European College of Sport Science tenutosi a Prague nel 2019.

Neuromuscular fatigue in elbow flexors vs. knee extensors after arm-cranking and cycling exercises

M. Colosio;L. Rasica
Secondo
;
G. Vernillo;
2019-07

Abstract

Introduction Neuromuscular fatigue is defined as a reversible, time-dependent decline in the maximal force-generating capacity of a muscle originating at both central and/or peripheral levels. Previous data inferred from sustained isometric contractions suggest that elbow flexors (EF) and knee extensors (KE) present different magnitudes of global, central and peripheral fatigue. During dynamic exercises, contribution of these components may vary according to different muscle perturbations coming from lower motor-unit discharge rate, even at high intensity, and a recovery period among contractions. The aim of this study was to evaluate the contribution of central and peripheral factors to neuromuscular fatigue in EF vs. KE after arm-cranking and cycling exercises. Methods Eleven physically active men (age: 23.8±2.4ys) participated in the study and performed in a pseudo-randomised and counterbalanced order two incremental exercises (INCR) until exhaustion on either a cycle- (CYCLE) or an arm- (ARM) ergometer. During INCR, breath-by-breath pulmonary oxygen uptake (V’O2) and heart rate (HR) were evaluated. Neuromuscular function of KE (quadriceps muscle) and EF (biceps brachii) was assessed before (PRE), 2 min (POST) and 20 min (POST20) after INCR cessation during maximal voluntary contractions and in relaxed muscles. Global fatigue was assessed from maximal isometric force (MVF) during maximal voluntary contractions. To quantify central fatigue, voluntary activation (VA) levels were determined by the adapted twitch interpolation technique. To identify peripheral fatigue, high- (100 Hz, Db100), low- (10 Hz, Db10) frequency doublets and single twitches (Tw) were delivered to the relaxed muscle. The presence of low-frequency fatigue (LFF) was evaluated from the change in the Db10:Db100 ratio. Surface electromyography sensors were placed in correspondence of the vastus medialis, vastus lateralis, and rectus femoris or biceps brachii. Results At the end of INCR, time to exhaustion was not different between CYCLE and ARM (802±93 vs. 886±164 s, p<0.01). V’O2 was higher in CYCLE than ARM (3.41±0.50 vs. 2.47±0.60 L*min-1, p<0.001). At POST, MVF decreased after both CYCLE (21±13%) and ARM (26±7%). At POST20, MVF recovered to resting values in KE ( ̴4% of PRE) while it partially recovered in EF ( ̴17% of PRE). VA was not different in all conditions for both KE and EF. At POST, Db100 (-30%) and LFF (-28%) were significantly reduced in both KE and EF (p<0.01). At POST20, Db100 partially recovered ( ̴15% of PRE) in both KE and EF while LFF did not significantly recovered in EF. Conclusion The present results suggest that neuromuscular fatigue of knee extensors and elbow flexors after incremental exercise mainly originates at peripheral level, with peripheral fatigue still presents in elbow flexors after 20 min of recovery. Thus, recovery from dynamic exercises involving lower or upper limbs should take into account the higher contribution of peripheral factors on muscle fatigue in elbow flexors.
Settore M-EDF/02 - Metodi e Didattiche delle Attivita' Sportive
Neuromuscular fatigue in elbow flexors vs. knee extensors after arm-cranking and cycling exercises / M. Colosio, L. Rasica, G. Baldassarre, G. Vernillo, M. Marzorati, S. Porcelli. ((Intervento presentato al 24. convegno European College of Sport Science tenutosi a Prague nel 2019.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/642099
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