Influence of chronotype and habitual training time-of-day on rating of perceived exertion in young adults

INTRODUCTION: To date, there has been little agreement on circadian variation in sports performance. It seems that both chronotype and habitual training time-of-day (HTT) need to be considered when assessing diurnal variation in performance [1]. Therefore, the aim of this study was to evaluate if chronotype and HTT may influence the rating of perceived exertion (RPE) after two different intensity trials performed in three times of day. METHODS: The chronotype of participants (N56: age 23.8±2.1 yrs, BMI 22.1±2.0 kg/m2, V’O2max 40.1±9.1 ml/kg/min) was assessed using the Morningness Eveningness Questionnaire (MEQ) [2] and their maximal oxygen uptake (V’O2max) was determined via direct gas analysis (Fitmate-Pro, Cosmed, Italy) on a cycle ergometer (LC6, Monark, Sweden) using a submaximal exercise-based protocol. Subjects’ HTT was objectively evaluated using an activity monitor (Lifecorder Plus, Kenz, Japan) worn for one week. Participants performed two 6-minute bouts of exercise on cycle ergometer at 60% and 90% of V’O2max at 8.30am (morning trial, MT), at 1.00pm (afternoon trial, AT) and at 5.30pm (evening trial, ET) in a randomised order. Training sessions were interspersed by 48 hours. After each session, participants reported their RPE (CR10) [3]. RESULTS: Distributions of chronotype and HTT were 27% of Morning-types (M-type), 59% of Neither-types (N-type) and 14% of Eveningtypes (E-type) and 21% of subjects trained in the morning, 55% in the afternoon and 23% in the evening, respectively. When the RPE of all the subjects were examined as a whole, there was no difference between the MT, the AT and the ET (60% V’O2max MT: 3.0±1.5, AT: 2.9±1.4, ET: 2.8±1.5; 90% V’O2max MT: 7.3±2.4, AT: 7.1±2.4, ET: 7.0±2.3). No time-by-group interaction effect on RPE was observed when participants were grouped by chronotype (60% V’O2max p=0.2931; 90% V’O2max p=0.7653) or HTT (60% V’O2max p=0.9370; 90% V’O2max p=0.9862). However, M-type reported lower RPE scores post MT and E-type post ET both at moderate (60% V’O2max Mtype_MT: 2.6±1.1, AT: 3.3±1.7, ET: 3.1±1.5; E-type_ MT: 3.3±2.0, AT: 2.7±0.9, ET: 2.6±1.8) and vigorous (90% V’O2max M-type_MT: 6.8±2.7, AT: 7.3±2.8, ET: 7.4±2.1; E-type_ MT: 7.4±2.2, AT: 7.0±1.9, ET: 6.4±2.5) exercise intensity. Interestingly, the same trend was not observed for RPE and HTT. CONCLUSION: In contrast to previous study findings [1], neither chronotype nor HTT have significantly influenced diurnal variation in RPE. Nevertheless, the lowest RPE scores found post MT for M-type and post ET for E-type, regardless of their HTT, seem to suggest that only chronotype might influence RPE. Future research needs to confirm this hypothesi