Title

The effects of circadian rhythmicity of salivary cortisol and testosterone on maximal isometric force, maximal dynamic force production and power output

Date of Award

2009

Degree Type

Thesis

Degree Name

Master of Science (Sports Science)

School

School of Exercise, Bio1nedical and Health Sciences

First Advisor

Michael McGuigan

Second Advisor

Michael Newton

Abstract

The purpose of the study was to investigate the effects of circadian rhythm (CR) of salivary cortisol (C) and testosterone (T) on maximal isometric and dynamic force production (Fpeak), and power output (Ppeak). Twenty male university students (mean age= 23.8 ± 3.6, mean± standard deviation; height= 177.5 ± 6.4cm, weight= 78.9 ± 11.2kg) with at least 1 year of resistance training experience were recruited as subjects. Session one was used for the collection of subject's physical data (ie. height, weight and aural temperature [Taural). An evaluation of morningness-eveningness was also performed using the Home and Ostberg questionnaire (1976). Saliva samples were collected at 4 different times of the day (0800 hours, 1200 hours, 1600 hours, and 2000 hours) to assess C and T levels at those times. The second testing session was used as a familiarisation session for subjects and also to establish baseline strength and power measurements. Subjects performed a battery of 4 different tests for the assessment of strength and power in the following order; 3 trials of counter-movement jumps (CMJ), 3 trials of squat jumps (SJ), 3 trials of isometric mid-thigh pull (IMTP), and a 1RM squat. After the session ended, subjects were requested to sit quietly for 15 minutes to 30 minutes before a session rating of perceived exertion (RPE) score was collected based on a Borg's CR-10 RPE scale. Sessions 3 to 6 were kept identical to the familiarisation session with the exception of randomised start times. The results showed that Fpeak and peak rate of force development (RFDpeak) presented a clear CR in CMJ, IMTP, but not significant in SJ. A distinct CR in P peak and jump height (HT max) was also clearly present in CMJ, but not significant in SJ. One repetition max squat did not show any fluctuations in weight lifted with the exception of values obtained at 0800 hours. Ratings of perceived exertion collected at 0800 hours and 2000 hours were found to be higher with 1200 hours and 1600 hours being significantly (p:≤0.05) lower. Salivary T and C also showed clear CR elevated highest values at 0800 hours and lowest values at 2000 hours, however, TIC ratios did not seem to display any variations with the exception of 0800 hours being elevated. The results, however, did show a very strong correlation between Taural with Fpeak and Ppeak (r=0.86 and r=0.8, p:≤0.001). The study showed the existence of a CR in isometric Fpeak dynamic Fpeak and Ppeak in certain testing modalities. Stretch-shortening cycle component seemed to be more sensitive to a time-of-day variation. The findings do show an increase in physical performance was concomitant with an increase in body temperature, suggesting that it would be a better indicator of physical performance.

LCSH Subject Headings

Circadian rhythms - Physiological aspects.

Exercise - Physiological aspects.

Hydrocortisone - Physiological effect.

Testosterone - Physiological effect.

Access Note

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