The Effect Of Chronotype On The Dose-Response To Field-Based Training In Elite Rugby League

Abstract

Rugby League (RL) seasons are often congested, with matches often being played within the afternoon and evening hours. Despite this, training commonly occurs within the morning hours. To our knowledge, the impact of the start time of training and the impact of chronotype is yet to be examined in a RL context. PURPOSE: to examine the effect of chronotype and circadian variation on the dose-response to field-based training in elite RL. METHODS: 22 male RL players from a single National Rugby League club volunteered to participate in the study. Their chronotype was categorised by a newly validated index, the Athlete Specific Chronotype Index (ACTi). Training start time was categorised as morning (before midday), afternoon (12:00 to 18:00 h) or evening (after 18:00 h). Physical performance was recorded during 47 pre-season and 67 in-season main training sessions, using GPS units sampling at 10 Hz (Optimeye S5, Catapult Interventions, Scorsby, Australia). Performance metrics included relative distance covered (m·min-1), relative high speed running distance (HSR (m·min-1); > 14.4 km·h-1), PlayerLoad 2D (arbitrary units; AU) PlayerLoad slow (AU) and acceleration load (AU). Perceptual measures included self-reported wellness (sleep quality and readiness to train) and session ratings of perceived exhaustion (sRPE). RESULTS: 11 players were categorised as morning types, 10 as intermediate types and one as an evening type. There was no influence of chronotype on pre-training wellness measures (p = 0.35 - 0.75). Start time of main training sessions influenced readiness (p = 0.002) and sleep quality (p < 0.001) with a 0.20 AU increase in readiness and a 0.57 AU increase in sleep quality between 07:00 and 19:00 h. No influence of chronotype was found on the sRPE response to external load (p = 0.12 - 0.63). The start time of main training sessions affected the sRPE response to PlayerLoad slow (p = 0.004) and acceleration load (p = 0.01). Post-hoc analysis revealed a lower sRPE response to PlayerLoad slow and acceleration load within the evening training sessions compared to morning and afternoons. CONCLUSION: The majority of athletes were categorised as earlier chronotypes, however they showed improved wellness prior to evening sessions and reduced sRPE responses to accelerometer and locomotor based metrics within these sessions.