Author(s): ABU-TALIP, N.K., ŠKARABOT, J., BALSHAW, T.G., Institution: LOUGHBOROUGH UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 2460

INTRODUCTION:
Muscular force production is mediated by descending pathways including the corticospinal (CST) and reticulospinal (RST) tract. Whilst the CST has been extensively investigated within the context of neural adaptation to resistance training, RST adaptability has received less attention. RST fibres originate in the reticular formation, a deep lying structure within the brain stem, precluding non-invasive stimulation in humans. The development of methodologies assessing voluntary reaction time (RT) or evoked electrophysiological responses preceded by loud auditory startles (AS; >110 dB) relative to those without prior AS has provided a cluster of indirect techniques that can allow RST adaptability to be experimentally tested. However, the between-day reliability of these indirect RST measures remains under investigated. The purpose of this study was to determine between-day reliability of RST properties derived from voluntary (StartReact paradigm) and evoked (motor evoked potential [MEP] and cervicomedullary motor evoked potential [CMEP]) measures in elbow flexors.
METHODS:
Healthy young adults (n=6; 4 males, 2 females) completed a familiarisation session and 3 identical main measurement sessions on separate days at a consistent time to establish between-day reliability of: (i) elbow flexion isometric maximum voluntary force (MVF); (ii) surface EMG of the biceps brachii long head during MVF (BBL-EMGMVF); (iii) peak-to-peak BBL Mmax amplitude; (iv) BBL RSTgain ratio ([visual cue RT - visual auditory cue RT] ÷ [visual cue RT – visual starling cue RT]) produced from the StartReact paradigm; (v) the BBL conditioned/control MEP ratio (conditioned MEP preceded by a 50 ms AS); and (vi) the BBL conditioned/control CMEP ratio (conditioned CMEP preceded by a 70 ms AS). CMEP and MEP were superimposed during submaximal contractions whilst a rectified and smoothed (0.5 s epoch) real-time EMG signal was matched to a target of 10%BBL-EMGMVF. Between-day reliability was assessed using within-participant coefficient of variation (CVw; [SD ÷ Mean] x 100) and one-way ANOVAs.
RESULTS:
There were no differences between test days 1, 2 and 3 for the included variables (ANOVA, 0.33≤p≤0.96). The CVw for MVF, BBL-EMGMVF, BBL Mmax, BBL RSTgain ratio (Day 1: 0.78 ± 0.10, Day 2: 0.76 ± 0.12, Day 3: 0.85 ± 0.08), BBL conditioned/control MEP ratio (Day 1: 0.86 ± 0.16, Day 2: 0.76 ± 0.14, Day 3: 0.75 ± 0.11), and BBL conditioned/control CMEP ratio (Day 1: 1.47 ± 0.54, Day 2: 1.38 ± 0.37, Day 3: 1.56 ± 0.28) was 5.2 ± 2.6%, 20.8 ± 14.8%, 15.1 ± 10.6%, 8.6 ± 7.6%, 17.0 ± 5.0%, and 21.4 ± 9.3%, respectively.
CONCLUSION:
The results of this study provide a preliminary indication of between-day reliability for a cluster of indirect measures for assessing the properties of the human RST within an isometric elbow flexion model and have implications for the interpretation of RST adaptability within the context of subsequent longitudinal resistance training intervention studies.