Is there a diurnal variation in flexibility in extreme morning and evening-types where a standardised approach has been employed: Effect of an extended warm-up in the morning?

Evidence of a diurnal variation on flexibility is equivocal in the literature. This is in part due to familiarisation of the participant to the test, inter-individual variation in chronotype ("morningness" and "eveningness"), bias due to methodological issues and outcome, as well as level of warm-up before the measure. Therefore, the main objective of this study was to establish the effects of time-of-day on flexibility in eight outright "morning-type" [M] and eight "evening-type" [E] where a "standardised protocol" has been employed to reduce bias. A second objective was to determine the effect of a 30-min warm-up on the early morning measures of flexibility. Sixteen recreationally active adults, eight M-types (three males and five females) and eight E-types (three males and five females) were recruited. The participants completed (i) a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover><mml:mi>V</mml:mi><mml:mo>˙</mml:mo></mml:mover></mml:math>O₂ peak test on a cycle ergometer, (ii) three familiarisations where intra-aural (T_IA) temperature was measured at rest and after a 5-min warm-up on a cycle ergometer. Thereafter, participants undertook grip strength (right and left hand), subjective arousal (0-10 cm Likert scale), and a battery of five static flexibility tests. Measuring whole-body range of movement (ROM, cm), spinal ROM during hyper-extension (º), lateral ROM of the spine (º), and ROM during ankle plantar-flexion and dorsi-flexion (º). Thereafter, iii) five experimental sessions (using the same protocol) at 08:00, 12:00, 16:00, 20:00 and a further 08:00 h session (administered in a counterbalanced order), where a 30-min warm-up at 70% of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover><mml:mi>V</mml:mi><mml:mo>˙</mml:mo></mml:mover></mml:math>O₂ peak was performed on a cycle ergometer. Each session was separated by 48-h. Data were analysed using general linear models with repeated measures. M-type showed greater ankle dorsi-flexion than E-types (8.0ºROM). Diurnal variations (08:00-20:00 h) in temperature (T_IA, Δ0.64ºC), whole-body flexibility (Δ3.0 cm), lateral-movement of the spine (Δ4.4ºROM), ankle dorsi-flexion (1.9ºROM), right grip strength (Δ4.0N), and arousal (Δ2.4 cm) were observed (<i>p</i> < 0.05); the highest values for all variables were recorded at 16:00 h, apart from arousal which peaked at 12:00 h. Resting T_IA showed a significant interaction between chronotype and time-of-day where the peak in the M-type was 16 h and E-type later at 20 h (<i>p</i> = 0.002); although not significant there was a trend for the M-type profiles for whole-body flexibility to decrease from 16 to 20 h and E-types to plateau following the temperature profile (<i>p</i> = 0.093). The 30-min warm-up in the morning showed an increase in T_IA temperature of 0.58 ± 0.41°C and whole-body flexibility (2.4 ± 2.5 cm) which is measured with specially designed apparatus compared to the morning session with 5-min warm-up. The other flexibility measures which involved goniometry showed no detectable effect under current measurement precision for both time-of-day and a 30-min warm-up. M-types showed a greater increase in ankle dorsi-flexion flexibility than E-types after the extended warm-up (Δ2.3°ROM).