RESUMEN
Experiencing pain in one leg can alter exercise tolerance and neuromuscular fatigue (NMF) responses in the contralateral leg; however, the corticospinal modulations to nonlocal experimental pain induced by blood flow occlusion remain unknown. In three randomized visits, 13 male participants performed 25% of isometric maximal voluntary contraction (25%IMVC) to task failure with one leg preceded by (i) 6-min rest (CON), (ii) cycling at 80% of peak power output until task failure with the contralateral leg (CYCL), or (iii) CYCL followed by blood flow occlusion (OCCL) during 25%IMVC. NMF assessments (IMVC, voluntary activation [VA], and potentiated twitch [Qtw]) were performed at baseline and task failure. During the 25%IMVC, transcranial magnetic stimulations were performed to obtain motor-evoked potential (MEP), silent period (SP), and short intracortical inhibition (SICI). 25%IMVC was the shortest in OCCL (105 ± 50s) and shorter in CYCL (154 ± 68 s) than CON (219 ± 105 s) (p < 0.05). IMVC declined less after OCCL (-24 ± 19%) and CYCL (-27 ± 18%), then CON (-35 ± 11%) (p < 0.05). Qtw declined less in OCCL (-40 ± 25%) compared to CYCL (-50 ± 22%) and CON (-50 ± 21%) (p < 0.05). VA was similar amongst conditions. MEP and SP increased and SICI decreased throughout the task, while SP was longer for OCCL compared to CYC condition (p < 0.05). The results suggest that pain in one leg diminishes contralateral limb exercise tolerance and NMF development and modulate corticospinal inhibition in males. Novelty: Pain in one leg diminished MVC and twitch force decline in the contralateral limb. Experimental pain induced by blood flow occlusion may modulation corticospinal inhibition of the neural circuitries innervating the contralateral exercise limb.
Asunto(s)
Tolerancia al Ejercicio , Fatiga Muscular , Electromiografía , Potenciales Evocados Motores/fisiología , Humanos , Pierna , Masculino , Contracción Muscular/fisiología , Fatiga Muscular/fisiología , Músculo Esquelético/fisiología , Dolor , Estimulación Magnética TranscranealRESUMEN
Maximal voluntary contraction force (MVC), potentiated twitch force (Qpot), and voluntary activation (%VA) recover to baseline within 90 s following extreme-intensity exercise. However, methodological limitations mask important recovery kinetics. We hypothesized reductions in MVC, Qpot, and %VA at task failure following extreme-intensity exercise would be less than following severe-intensity exercise, and Qpot and MVC following extreme-intensity exercise would show significant recovery within 120 s but remain depressed following severe-intensity exercise. Twelve subjects (6 men) completed 2 severe-intensity (40, 50% MVC) and 2 extreme-intensity (70, 80% MVC) isometric knee-extension exercise bouts to task failure (Tlim). Neuromuscular function was measured at baseline, Tlim, and through 150 s of recovery. Each intensity significantly reduced MVC and Qpot compared with baseline. MVC was greater at Tlim (p < 0.01) and at 150 s of recovery (p = 0.004) following exercise at 80% MVC compared with severe-intensity exercise. Partial recovery of MVC and Qpot were detected within 150 s following Tlim for each exercise intensity; Qpot recovered to baseline values within 150 s of recovery following exercise at 80% MVC. No differences in %VA were detected pre- to post-exercise or across recovery for any intensity. Although further analysis showed sex-specific differences in MVC and Qpot, future studies should closely examine sex-dependent responses to extreme-intensity exercise. It is clear, however, that these data reinforce that mechanisms limiting exercise tolerance during extreme-intensity exercise recover quickly. Novelty: Severe- and extreme-intensity exercise cause independent responses in fatigue accumulation and the subsequent recovery time courses. Recovery of MVC and Qpot occurs much faster following extreme-intensity exercise in both men and women.
Asunto(s)
Fatiga Muscular , Músculo Esquelético , Electromiografía , Ejercicio Físico/fisiología , Tolerancia al Ejercicio/fisiología , Femenino , Humanos , Contracción Isométrica/fisiología , Rodilla/fisiología , Masculino , Fatiga Muscular/fisiología , Músculo Esquelético/fisiologíaRESUMEN
Data are scant on sex-related differences for electrically evoked contractions, which assess intrinsic contractile properties while limiting spinal and supraspinal adaptations to mitigate fatigue. Furthermore, the few studies that exist use stimulus frequencies considerably higher than the natural motor unit discharge rate for the target force. The purpose of this study was to compare force loss to electrically evoked contractions at a physiological stimulus frequency among young females (n = 12), young males (n = 12), old females (n = 11), and old males (n = 11). The quadriceps of the dominant leg were fatigued by 3 min of intermittent transcutaneous muscle belly stimulation (15 Hz stimulus train to initially evoke 25% of maximal voluntary force). Impairment of tetanic contractile impulse (area under the curve) did not differ between sexes for young or old adults or between age groups, with a pooled value of 55.2% ± 12.4% control at the end of fatigue. These data contrast with previous findings at 30 Hz, when the quadriceps of females had greater fatigue resistance than males for young and old adults. The present results highlight the impact stimulus frequency has on intrinsic fatigability of muscle; the findings have implications for future fatigue paradigms and treatment approaches when utilizing electrical stimulation for rehabilitation. Novelty Fatigue was not different between sexes with a stimulation frequency comparable to discharge rates during voluntary contractions. These results highlight that stimulus frequency not only influences fatigue development but also between-group differences.
Asunto(s)
Estimulación Eléctrica , Contracción Muscular , Fatiga Muscular , Músculo Cuádriceps/fisiología , Anciano , Femenino , Humanos , Rodilla , Masculino , Persona de Mediana Edad , Adulto JovenRESUMEN
The effect of localised head and neck per-cooling on central and peripheral fatigue during high thermal strain was investigated. Fourteen participants cycled for 60 min at 50% peak oxygen uptake on 3 occasions: thermoneutral control (CON; 18 °C), hot (HOT; 35 °C), and HOT with head and neck cooling (HOTcooling). Maximal voluntary force (MVF) and central activation ratio (CAR) of the knee extensors were measured every 30 s during a sustained maximal voluntary contraction (MVC). Triplet peak force was measured following cycling, before and after the MVC. Rectal temperatures were higher in HOTcooling (39.2 ± 0.6 °C) and HOT (39.3 ± 0.5 °C) than CON (38.1 ± 0.3 °C; P < 0.05). Head and neck thermal sensation was similar in HOTcooling (4.2 ± 1.4) and CON (4.4 ± 0.9; P > 0.05) but lower than HOT (5.9 ± 1.5; P < 0.05). MVF and CAR were lower in HOT than CON throughout the MVC (P < 0.05). MVF and CAR were also lower in HOTcooling than CON at 5, 60, and 120 s, but similar at 30 and 90 s into the MVC (P > 0.05). Furthermore, they were greater in HOTcooling than HOT at 30 s, whilst triplet peak force was preserved in HOT after MVC. These results provide evidence that central fatigue following exercise in the heat is partially attenuated with head and neck cooling, which may be at the expense of greater peripheral fatigue. Novelty Central fatigue was greatest during hyperthermia. Head and neck cooling partially attenuated the greater central fatigue in the heat. Per-cooling led to more voluntary force production and more peripheral fatigue.
Asunto(s)
Frío , Ejercicio Físico , Fatiga Muscular , Adulto , Electromiografía , Cabeza , Calor , Humanos , Péptidos y Proteínas de Señalización Intracelular , Contracción Isométrica , Masculino , Proteínas Serina-Treonina Quinasas , Adulto JovenRESUMEN
The majority of studies have routinely measured neuromuscular (NM) fatigue with a delay (â¼1-3 min) after cycling exercises. This is problematic since NM fatigue can massively recover within the first 1-2 min after exercise. This study investigated the etiology of knee extensors (KE) NM fatigue and recovery kinetics in response to cycling exercises by assessing NM function as early as 10 s following cycling and up to 8 min of recovery. Ten young males performed different cycling exercises on different days: a Wingate (WING), a 10-min task at severe-intensity (SEV), and a 90-min task at moderate-intensity (MOD). Electrically evoked and isometric maximal voluntary contractions (IMVC) of KE were assessed before, after, and during recovery. SEV induced the highest decrease in IMVC. Peak twitch (Pt) was more reduced in WING and SEV than in MOD (p < 0.001), whereas voluntary activation decreased more after MOD than WING (p = 0.043). Regarding Pt and the ratio between low- and high-frequency doublet (i.e., low-frequency fatigue), recovery was faster for WING, whereas IMVC and high-frequency doublet recovered slower during MOD (p < 0.05). Our results confirm that peripheral fatigue is greater after WING and SEV, while central fatigue is greater following MOD. Peripheral fatigue can substantially recover within minutes after a supramaximal exercise while NM function recovered slower after prolonged, moderate-intensity exercise. This study provides an accurate estimation of NM fatigue and recovery kinetics because of dynamic exercise with large muscle mass by significantly shortening the delay for postexercise measurements.
Asunto(s)
Ciclismo/fisiología , Ergometría , Fatiga Muscular , Adulto , Electromiografía , Humanos , Contracción Isométrica , Cinética , Masculino , Adulto JovenRESUMEN
The present study investigated the effects of exercise-induced elbow flexor fatigue on voluntary force output, electromyographic (EMG) activity and motoneurone excitability of the nonexercised knee extensor muscles. Eleven participants attended 3 testing sessions: (i) control, (ii) unilateral fatiguing elbow flexion and (iii) bilateral fatiguing elbow flexion (BiFlex). The nonfatigued knee extensor muscles were assessed with thoracic motor evoked potentials (TMEPs), maximal compound muscle action potential (Mmax), knee extensor maximal voluntary contractions (MVCs), and normalized EMG activity before and at 30 s, 3 min, and 5 min postexercise. BiFlex showed significantly lower (Δ = -18%, p = 0.03) vastus lateralis (VL) normalized EMG activity compared with the control session whereas knee extension MVC force did not show any statistical difference between the 3 conditions (p = 0.12). The TMEP·Mmax(-1) ratio measured at the VL showed a significantly higher value (Δ = +46%, p = 0.003) following BiFlex compared with the control condition at 30 s postexercise. The results suggest that the lower VL normalized EMG following BiFlex might have been due to a reduction in supraspinal motor output because spinal motoneuronal responses demonstrated substantially higher value (30 s postexercise) and peripheral excitability (compound muscle action potential) showed no change following BiFelex than control condition.