The circadian rhythm is a 24-hour cycle present within most biological systems that is controlled by the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN is responsible for synchronizing the peripheral "clocks" present in other tissues so that all rhythms, such as heart rate, body temperature, and hormone secretion, are functioning together. As most systems experience a circadian rhythm, physical performance likely does as well. Previous studies have investigated time of day effects on maximal strength, power, and endurance performance, however, factors (e.g., sex, chronotype, age, etc.) have not clearly been distinguished. Additionally, body temperature has been suggested to be the primary mechanism behind time of day variation, but there have been studies to suggest that this is not the only mechanism that impacts potential differences. Additionally, studies to date lack female participants, despite potential differences between sexes. Therefore, this series of studies aimed to determine optimal time of day for maximal strength and power activities. It also aimed to examine sex differences, and the effect of chronotype and body temperature on performance. To do this, 3 studies have been conducted. First, a maximal effort sprint test on a non-motorized treadmill was conducted in a sample of recreationally active males and females. Second, a reliability study was conducted to establish a protocol that could assess maximal strength and endurance during the same assessment. This protocol also can be used in any population. Lastly, this protocol was then used to assess time of day effects on maximal strength and critical force (a theoretical sustainable force output) at different times. This study used a sample of both males and females as well to evaluate sex differences.
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Doctor of Philosophy (Ph.D.)
College of Health Professions and Sciences
School of Kinesiology and Physical Therapy
Length of Campus-only Access
Doctoral Dissertation (Campus-only Access)
Renziehausen, Justine, "Time of Day Effects on Maximal Effort Strength/Power and Fatigability Assessments" (2023). Electronic Theses and Dissertations, 2020-. 1644.
Restricted to the UCF community until May 2024; it will then be open access.