The fluid replacement needs of young tennis players : implications for tennis coaches.

A Thesis Submitted to the Faculty of Education, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master in EducationThis study aimed to assess selected physiological, osmoregulatory and thermoregulatory responses to tennis play in children, Twenty-four young male tennis players (X age; 13.3+ 1.31 years) were stndied while playing for 90 min under warm environmental conditions (WBGT index= 13-19). Ad libitum consumption of pure water was permitted. Questionnaires were used in order to elicit information regarding the health status, degree of aeelimatizationnnd pre-match trait and state anxiety of the subjects. The physiological variables assessed. included pre- and post-match rectal temperature (T), heart rate (HR) and oxygen consumption (02) during the match. The biochemical observations included pre- and postmatch blood glucose, haematoerit (Ret), haemoglobin (lIb), plasma electrolyte (Na", Cl', K+, Mg++) and total plasma protein (TPP) concentrations. The findings )q~ed that the young tennis players investigated in this study experienced, ~de!'ate levels of pre-competitive trait and state amdety. The estimated nie.m exercise intensity of 50-55% of VOzmax for a duration of 90 min resulted. in a Tre increase of 0.73 •C. Mean percentage dehydration was 0.MO+O.25. Plasma volume (PV) changes were insignificant and were positively related to TPP changes. Mean plasma. Na" and CI- concentrations increased by 0.88 mmol.r" and 2.2 mmol.r:' respectively. The subjects' mean H... response (145 bpm) of a subset or the sample(n=13) and estimated VOz (21.38 ml.kg-l.min-~ represented a 55% of the age adjusted HRmax reserve and approximately a 50-55% of V02 max respectively. The time spent within the target heart rate range (60-85% HR. max reserve) comprised only 33% of the match duration. Mean energy expenditure was estimated to be 1772 KJ dUl'ing the 90 min period. Itwas calculated that in order to prevent harmful levels of dehydration under warm environmental conditions and at an exercise intensity of tennis play of approximately 55% of the age adjusted HR max reserve or 50-55% of V02 max, consumption of 4.44-6.81 mI.Kg-1.br-1 or 200-360 ml.hr" of water is recommended in young tennis players possessing a body mass of 45-53 Kg. The precise quantity was concluded to be a function of the mass and exercise intensity of the subjects and the environmental heat stress index during play.Andrew Chakane 201