Arm-cycling sprints induce neuromuscular fatigue of the elbow flexors and alter corticospinal excitability of the biceps brachii

Abstract

We examined the effects of arm-cycling sprints on maximal voluntary elbow flexion and corticospinal excitability of the biceps brachii. Recreationally trained athletes performed ten 10-s arm-cycling sprints interspersed with 150 s of rest in 2 separate experiments. In experiment A (n = 12), maximal voluntary contraction (MVC) force of the elbow flexors was measured at pre-sprint 1, post-sprint 5, and post-sprint 10. Participants received electrical motor point stimulation during and following the elbow flexor MVCs to estimate voluntary activation (VA). In experiment B (n = 7 participants from experiment A), supraspinal and spinal excitability of the biceps brachii were measured via transcranial magnetic and transmastoid electrical stimulation that produced motor evoked potentials (MEPs) and cervicomedullary motor evoked potentials (CMEPs), respectively, during a 5% isometric MVC at pre-sprint 1, post-sprint 1, post-sprint 5, and post-sprint 10. In experiment A, mean power output, MVC force, potentiated twitch force, and VA decreased 13.1% (p < 0.001), 8.7% (p = 0.036), 27.6% (p = 0.003), and 5.6% (p = 0.037), respectively, from pre-sprint 1 to post-sprint 10. In experiment B, (i) MEPs decreased 42.1% (p = 0.002) from pre-sprint 1 to post-sprint 5 and increased 40.1% (p = 0.038) from post-sprint 5 to post-sprint 10 and (ii) CMEPs increased 28.5% (p = 0.045) from post-sprint 1 to post-sprint 10. Overall, arm-cycling sprints caused neuromuscular fatigue of the elbow flexors, which corresponded with decreased supraspinal and increased spinal excitability of the biceps brachii. The different post-sprint effects on supraspinal and spinal excitability may illustrate an inhibitory effect on supraspinal drive that reduces motor output and, therefore, decreases arm-cycling sprint performance.

Corticospinal excitability during fatiguing whole body exercise

“…At first sight, this would appear to be different from the findings in a resting muscle which suggest that the corticospinal pathway is depressed following fatiguing whole body exercise. However, in the presence of unchanged MEPs, CMEPs (amplitude and area) appear to be increased following exhaustive cycling (Sidhu et al, 2017) and fatiguing arm cycling sprints (Pearcey et al, 2016). Thus, in the limited number of studies testing motoneuronal excitability, motor cortical excitability was decreased which agrees with the outcome of the studies using a resting muscle to assess corticospinal excitability (Ross et al, 2010; Verin et al, 2004).…”

Maximal Voluntary Activation of the Elbow Flexors Is under Predicted by Transcranial Magnetic Stimulation Compared to Motor Point Stimulation Prior to and Following Muscle Fatigue

“…Electrical stimulation was delivered via a cathode placed on the skin over the biceps motor point and an anode on the brachii distal tendon (Smith et al, 2007 ; Khan et al, 2011 ; Monks et al, 2016 ; Pearcey et al, 2016 ). Current pulses were delivered as a doublet (10 ms apart, 100 μs duration, 100–225 mA) via a constant current stimulator (DS7AH, Digitimer Ltd., Welwyn Garden City, UK).…”

“…Voluntary activation (VA) is the level of neural drive from the central nervous system to produce a given force output from a muscle. Examining how VA is estimated is important for quantifying the presence of central fatigue in clinical populations and for multiple research purposes (Taylor et al, 1996 ; Newham and Hsiao, 2001 ; Todd et al, 2003 , 2005 ; Prasartwuth et al, 2005 ; Hunter et al, 2008 ; Cahill et al, 2011 ; Pearcey et al, 2015 , 2016 ). The Interpolated Twitch Technique (ITT) was developed as a way to estimate central VA (Merton, 1954 ).…”

“…There is a non-equivalent TMS estimated twitch force and the nerve stimulation PT force amplitudes for both the elbow flexors (Todd et al, 2003 , 2004 , 2005 ; Smith et al, 2007 ; Kennedy et al, 2013 ), and knee extensors (Goodall et al, 2009 , 2012 , 2014 ; Sidhu et al, 2009b ; Klass et al, 2012 ). Fatigue in the central and peripheral nervous systems (Enoka and Stuart, 1992 ; Gandevia, 2001 ; Kent et al, 2016 ) reduces force production, alters SIT forces during submaximal voluntary contractions and MVCs and decreases estimated or resting PT forces (Todd et al, 2003 ; Goodall et al, 2009 ; Kennedy et al, 2013 ; Keller-Ross et al, 2014 ; Pearcey et al, 2015 , 2016 ). The linear relationship between voluntary force and TMS evoked SIT force also decreases with fatigue resulting in an altered estimated resting twitch force and subsequently an over or underestimation of VA (Hunter et al, 2006 , 2008 ; Kennedy et al, 2013 ; Yoon et al, 2013 ).…”

Understanding exercise-dependent plasticity of motoneurons using intracellular and intramuscular approaches

“…TMES activates spinal MNs via stimulation of the corticospinal tract (Ugawa et al 1991). These stimulation techniques have been used to determine how spinal MN excitability changes with varying intensities of voluntary contraction and fatigue (Collins et al 2018;Kennedy et al 2016;Martin et al 2006;Pearcey et al 2016;Todd et al 2003), during rhythmic and alternating activity (Forman et al 2014Power et al 2018), and due to resistance training (Carroll et al 2002;Pearcey et al 2014;Philpott et al 2015). It should be noted, however, that evoked potentials do not provide a measure of intrinsic MN excitability and are not analogous to intracellular measures of excitability (e.g., rheobase and input resistance) made in animal models.…”