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?
Level 2 - randomized trial
Counterbalanced repeated-measures crossover experimental study in healthy volunteers
PubMed 41574600 · doi:10.1080/07420528.2025.2611854
What was done
Sixteen recreationally active adults categorized as extreme morning-types (n = 8; 3 men, 5 women) or evening-types (n = 8; 3 men, 5 women) completed a VO2 peak test and three familiarization sessions. Participants then completed five counterbalanced experimental sessions spaced 48 hours apart at 08:00, 12:00, 16:00, and 20:00 h (after a 5-minute cycle ergometer warm-up), plus an additional 08:00 h session following an extended 30-minute warm-up at 70% VO2 peak. Measurements included intra-aural body temperature, grip strength, subjective arousal, and five static flexibility tests (whole-body range of motion [ROM], spinal hyper-extension, lateral spinal ROM, and ankle plantar-flexion/dorsi-flexion).
What was found
Morning-types exhibited greater baseline ankle dorsi-flexion than evening-types (difference of 8.0° ROM). Across the day (08:00–20:00 h), significant diurnal variations occurred (p < 0.05) in body temperature (Δ0.64°C), whole-body flexibility (Δ3.0 cm), lateral spinal ROM (Δ4.4°), ankle dorsi-flexion (1.9° ROM), right grip strength (Δ4.0 N), and subjective arousal (Δ2.4 cm). All variables peaked at 16:00 h, except arousal, which peaked at 12:00 h. Body temperature showed a significant chronotype-by-time interaction (p = 0.002), peaking at 16:00 h in morning-types and 20:00 h in evening-types. An extended 30-minute morning warm-up increased intra-aural temperature by 0.58 ± 0.41°C and whole-body flexibility by 2.4 ± 2.5 cm compared to a 5-minute warm-up, and morning-types gained more ankle dorsi-flexion ROM than evening-types (Δ2.3°). Goniometer-based flexibility tests lacked precision to detect time-of-day or warm-up differences.
Why it matters
The study demonstrates that human flexibility follows a diurnal rhythm closely aligned with core body temperature, peaking in the late afternoon. It also shows that a prolonged aerobic warm-up can offset morning stiffness, though chronotype influences specific joint responses.
Limits
The sample size was very small (16 participants total, 8 per chronotype), reducing statistical power for subgroup interactions. The cohort was limited to young, recreationally active extreme chronotypes, preventing generalization to intermediate chronotypes, older adults, or elite athletes. Goniometric joint measurement lacked sufficient precision to detect subtle time-of-day shifts in several joint angles.
Cited by
- supports In the late afternoon, resting heart rate is relatively higher, core body temperature is warmer, and muscle tone and joint flexibility are improved compared to the early morning.