Muscle activation of the knee extensors following high intensity endurance exercise in cyclists

Abstract

This study was conducted to assess the effects in trained cyclists of exhausting endurance cycle exercise (CE) on maximal isometric force production, surface electromyogram (EMG) and activation deficit (AD) of the knee extensors. Ten male subjects made four isometric maximal voluntary contractions (MVC) of the knee extensor muscles immediately prior (pre), 10 min after (post) and 6 h after completion of CE. The CE consisted of 30 min of exercise on a stationary cycle ergometer at an intensity corresponding to 80% of maximal oxygen uptake (VO(2max)) followed by four x 60-s periods at 120% of VO(2max). Two MVC were performed with recording of surface EMG from the knee extensors, whilst an additional two MVC were completed with percutaneous electrical muscle stimulation (EMS; 25 pulses at 100 Hz with the maximal tolerable current) superimposed over the maximal voluntary contraction force (MVF) but without EMG (to avoid interference). The MVF, integrated EMG (iEMG), and AD [calculated as the difference between MVF and the electrically stimulated force (ESF) during the EMS contractions] were statistically analysed. The MVF was significantly reduced (P < 0.05) post and 6-h post compared to pre-CE level. The iEMG was significantly reduced (P < 0.05) post and 6 h post CE. The ESF was also reduced, whilst AD was significantly increased (P < 0.05) post and 6-h post CE compared to the pre CE. These results suggest that the level of exercise stress administered in this study was sufficient to impair the central and peripheral mechanisms of force generation in knee extensors for a period of 6-h. Athletes engaged in concurrent training (strength and endurance) should consider this effect in exercise programming.

Endurance and strength training effects on physiological and muscular parameters during prolonged cycling

“…O 2max ) followed by four 60-s periods at 120% of V . O 2max , Bentley et al (2000) also observed a significant decrease in EMGi measured during an isoMVC preformed immediately after and also six hours later. For these authors, the level of exercise stress administered in this study was sufficient to impair the central and peripheral mechanisms of force generation in knee extensors for a period of 6 hours and athletes engaged in concurrent training (strength and endurance) should consider this effect in exercise programming.…”

The Effects of Combined Strength and Endurance Training on Running Performance the Following Day

“…16-24 hours) may provide su‹cient recovery from performing strength and endurance training sessions on the same day. This has been highlighted by previous studies where full recovery from high intensity endurance exercises occurred within 24 hours (Bentley, et al, 2000) and that no deletrious eŠects on sub-maximal running performance was found 24 hours following strength training (Marcora and Bosio, 2007).…”

“…This interference has been suggested to occur due to preceding endurance exercises compromising optimal force production during subsequent strength training sessions, known as the``acute hypothesis'' (Leveritt et al, 1999). Indeed, reports have shown that endurance training impairs maximal voluntary contraction (MVC) for 6 hours post training (Bentley et al, 2000), indicating that endurance exercises may cause detrimental eŠects on strength training performance. However, studies have also shown that strength training reduces MVC for over 48 hours (Brentano and Kruel, 2011;Hakkinen et al, 1988), suggesting that endurance performance may be impaired in the hours following a strength training session.…”

“…Studies have reported that MVC was compromised 6 hours post endurance training (Bentley et al, 2000) and 24 hours post strength training. Therefore, it is presumable that performing strength and endurance training sessions 6 hours apart on the same day will impair various performance measures the following day.…”

Fisiologia da fadiga muscular. Delimitação conceptual, modelos de estudo e mecanismos de fadiga de origem central e periférica

“…Alguns estudos (76,77,78,79,93,116) relacionaram as alterações de parâmetros cinemáticos induzidas pela fadiga na identificação de factores de risco para ocorrência de lesões de sobrecarga. O papel da fadiga neuromuscular na variação da proprioceptividade (2,47,81) e do controlo motor (54,81) tem sido, também, a par da influência da idade (89) , do sexo dos sujeitos (52,91,92,103) e da manifestação dos padrões de activação (9,90,93) e coactivação (49,59,118) de alguns grupos musculares, objectivo de alguns trabalhos neste domínio. Apesar do interesse de mais de um século por parte dos investigadores, os agentes definitivos indutores de fadiga encontram-se ainda por identificar.…”