Department of Sport, Exercise and Health, Faculty of Medicine, University of Basel , Basel , Switzerland.
Centre for Chronobiology, Psychiatric Hospital of the University of Basel , Basel , Switzerland.
Chronobiol Int. 2019 Nov;36(11):1537-1549. doi: 10.1080/07420528.2019.1658596. Epub 2019 Sep 2.
Time-of-day effects in strength performance have been extensively investigated due to their relevance in competitive sports. However, most studies use large measurement intervals making it difficult to monitor potential performance changes throughout the day. Furthermore, previous studies have exclusively focused on how the time of day affects strength on a group level and ignored the individual differences in the times of peak performance. Therefore, the main purpose of this study was to investigate the diurnal and day-to-day variations in isometric and isokinetic leg, arm and trunk strength over six different times of the day. Following a familiarization test, 19 trained males (age: 24.1 ± 2.5 years) performed isometric and isokinetic strength assessments at six different times of the day (7:00, 10:00, 13:00, 16:00, 19:00, and 21:00) with an isokinetic dynamometer. An eighth test session was performed at the same time of the day as the seventh test session to investigate the day-to-day variations and the difference between diurnal and day-to-day variations were compared. All tests were separated by at least 48 h. The start time for the first session was randomized. The mean maximum isometric leg strength was 5.85 ± 0.80 N.kg and 4.99 ± 0.78 N.kgat the peak and at the nadir of the day, respectively. The mean difference (95% CI) was 0.86 ± 0.47 N.kg (0.62; 1.10) for the diurnal variation and 0.30 ± 0.42 N.kg (0.09; 0.52) for the day-to-day variation. The mean maximum isometric arm strength was 1.68 ± 0.33 N.kg at the peak and 1.46 ± 0.19 N.kg at the nadir of the day, respectively. The mean difference (95% CI) was 0.21 ± 0.16 N.kg (0.14; 0.29) for the diurnal variation and 0.06 ± 0.05 N.kg (0.03; 0.08) for the day-to-day variation. The linear mixed-effects model showed little evidence for differences in isometric leg strength between the different times of the day (all -values >0.983). The present study demonstrated that diurnal variations in leg and arm strength are nearly three times higher than the day-to-day variations, but there was only little evidence for a time-of-day effect on a group level. The diurnal variations observed herein without time-of-day effects are suggestive that individuals achieve their peak performance at different times of the day. Therefore, performance tests should be carried out at the same time of the day to ensure comparability. Furthermore, depending on the difference between the time of competition and the time of peak performance, as well as the individual magnitude in diurnal variation, some athletes can have a clear disadvantage.: 95% CI, 95% confidence interval; SD, standard deviation; ICC, intraclass correlation coefficient.
由于其在竞技体育中的相关性，人们已经广泛研究了时间对力量表现的影响。然而，大多数研究使用较大的测量间隔，使得很难全天监测潜在的性能变化。此外，以前的研究仅关注时间如何影响群体水平的力量，而忽略了个体在最佳表现时间上的差异。因此，本研究的主要目的是调查一天中不同时间的等长和等速腿部、手臂和躯干力量的昼夜和每日变化。在熟悉测试后，19 名训练有素的男性（年龄：24.1 ± 2.5 岁）在一天中的六个不同时间（7:00、10:00、13:00、16:00、19:00 和 21:00）使用等速测力计进行等长和等速力量评估。第八次测试在第七次测试的同一时间进行，以研究每日变化，并比较昼夜变化和每日变化之间的差异。所有测试之间至少间隔 48 小时。第一次测试的开始时间是随机的。腿部最大等长力量的平均峰值为 5.85 ± 0.80 N.kg，低谷值为 4.99 ± 0.78 N.kg。昼夜变化的平均差异（95%CI）为 0.86 ± 0.47 N.kg（0.62；1.10），每日变化的平均差异为 0.30 ± 0.42 N.kg（0.09；0.52）。手臂最大等长力量的平均峰值为 1.68 ± 0.33 N.kg，低谷值为 1.46 ± 0.19 N.kg。昼夜变化的平均差异（95%CI）为 0.21 ± 0.16 N.kg（0.14；0.29），每日变化的平均差异为 0.06 ± 0.05 N.kg（0.03；0.08）。线性混合效应模型几乎没有证据表明不同时间的腿部等长力量存在差异（所有 - 值 >0.983）。本研究表明，腿部和手臂力量的昼夜变化几乎是每日变化的三倍，但在群体水平上几乎没有证据表明存在时间效应。本研究中观察到的没有时间效应的昼夜变化表明，个体在一天中的不同时间达到最佳表现。因此，为了确保可比性，应在同一时间进行性能测试。此外，根据比赛时间和最佳表现时间之间的差异，以及昼夜变化的个体幅度，一些运动员可能会处于明显的劣势。95%CI，95%置信区间；SD，标准偏差；ICC，组内相关系数。
