Interaction of Central and Peripheral Factors during Repeated Sprints at Different Levels of Arterial O2 Saturation

Abstract

PurposeTo investigate the interaction between the development of peripheral locomotor muscle fatigue, muscle recruitment and performance during repeated-sprint exercise (RSE).MethodIn a single-blind, randomised and cross-over design, ten male team-sport athletes performed two RSE (fifteen 5-s cycling sprints interspersed with 25 s of rest; power self-selected) in normoxia and in acute moderate hypoxia (FIO2 0.138). Mechanical work, total electromyographic intensity (summed quadriceps electromyograms, RMSsum) and muscle (vastus lateralis) and pre-fontal cortex near-infrared spectroscopy (NIRS) parameters were calculated for every sprint. Blood lactate concentration ([Lac-]) was measured throughout the protocol. Peripheral quadriceps fatigue was assessed via changes in potentiated quadriceps twitch force (ΔQtw,pot) pre- versus post-exercise in response to supra-maximal magnetic femoral nerve stimulation. The central activation ratio (QCAR) was used to quantify completeness of quadriceps activation.ResultsCompared with normoxia, hypoxia reduced arterial oxygen saturation (-13.7%, P=0.001), quadriceps RMSsum (-13.7%, P=0.022), QCAR (-3.3%, P=0.041) and total mechanical work (-8.3%, P=0.019). However, the magnitude of quadriceps fatigue induced by RSE was similar in the two conditions (ΔQtw,pot: -53.5% and -55.1%, P=0.71). The lower cycling performance in hypoxia occurred despite similar metabolic (muscle NIRS parameters and blood [Lac-]) and functional (twitch and M-wave) muscle states.ConclusionResults suggest that the central nervous system regulates quadriceps muscle recruitment and, thereby, performance to limit the development of muscle fatigue during intermittent, short sprints. This finding highlights the complex interaction between muscular perturbations and neural adjustments during sprint exercise, and further supports the presence of pacing during intermittent sprint exercise.

No Improved Performance With Repeated-Sprint Training in Hypoxia Versus Normoxia: A Double-Blind and Crossover Study

“…Provided that ∆[tHb] reflects blood perfusion, it is suggested that RS performance is not primarily limited by oxygen delivery to skeletal muscle, as this is indeed supported in the literature [24][25][26][27] , neither by blood flow-related removal of metabolites. Rather, RS performance is considered to be predominantly determined by neuromuscular factors 24-28 , including, but not limited to, neural drive, muscle excitability, PCr stores and recovery rate 28 .…”

A Combination of Amino Acids and Caffeine Enhances Sprint Running Capacity in a Hot, Hypoxic Environment

“…Mean power, peak power and peak velocities during the exercise protocol were recorded 8 by the treadmill force transducer at 25 Hz. Performance data were stored and analyzed as 141 described previously (Serpiello et al 2011 The knee extension protocol used has been described in detail elsewhere (Billaut et al 2013). …”

“…Before, at half-time, and immediately after exercise, participants were instructed to perform a stimulate each participant's quadriceps during the MVC (Amann et al 2007;Billaut et al 2013). …”

“…The protocol allowed the calculation of the tissue saturation index (TSI) for 197 cerebral tissue (Smith & Billaut 2010;Billaut et al 2013).…”

“…Cerebral oxygenation impairs central drive and motor unit recruitment during repeated-sprint 359 performance in hypoxic conditions (Smith & Billaut 2010;Billaut et al 2013), and other forms 360 of high-intensity exercise (Rooks et al 2010). Caffeine ingestion may reduce cerebral blood flow 361 and oxygen availability (Kennedy & Haskell 2011) …”