Objective: To assess physiological load in conjunction with individual patterns of match-play activity in junior female tennis players during actual singles tennis competition. Methods: Eight elite junior female tennis players (n = 8; mean (SD) age, 17.3 (1.9) years) took part in a 2 day invitational tournament. Activity pattern analysis was performed during competitive matches. Heart rate and blood lactate concentrations were measured during selected changeovers breaks in play. Results: The activity profile of junior female players were: rally duration, (mean (SD)) 8.2 (5.2) s; rest time between rallies, 17.7 (6.5) s; effective playing time, 21.9 (3.8)%; strokes per rally, 2.7 (1.7); changes of direction per rally, 2.3 (1.4). The mean (SD) heart rate and blood lactate concentration recorded during the matches were 161 (5) beats/min and 2.0 (0.8) mmol/litre. Heart rate and blood lactate concentration values were influenced by the characteristics of the match and mean (SD) heart rate was significantly higher (p = 0.004) during service games (166 (15.4) beats/min) than in return games (156 (19.6) beats/min), while blood lactate concentrations were not significantly different (p = 0.83) between service (2.3 (0.6) mmol/litre) and return games (2.3 (0.9) mmol/litre). We found a significant (p,0.05) positive relationship between rally duration, strokes per rally, changes of direction and blood lactate and heart rate responses, with stronger correlations when the players were serving. Conclusions: The physiological (ie, blood lactate and heart rate) responses associated with match play were influenced by the characteristics of the match (rally duration, strokes per rally and changes of direction), with higher heart rate on service position. Training programs should reflect these demands placed on female players during competitive match play.T he physical aspects related to singles tennis performance have been quite well studied in male participants. [1][2][3][4][5][6] Tennis match play is characterised by short bouts of intermittent exercise interrupted by several periods of longer duration and lower intensity. 7 Matches vary substantially in duration, often lasting more than an hour and in some cases more than 5 h. 4 7-9 Most matches consist of work and rest periods of 5-10 s and 10-20 s, respectively, interspersed with longer rest periods (ie, 90 s between changeover breaks). 7 During each point, players typically hit the ball an average of 2-3 times and make four directional changes per rally. 10 11 Match activity, however, can be influenced by factors such as court surface, ball type and sex. 12 13 In this regard, O'Donoghue and Ingram 12 have reported that rallies analysed in Grand Slam women's singles matches were significantly longer (7.1 s/rally) than those in men's singles matches (5.2 s/rally), together with a greater proportion of baseline rallies in women's singles. In addition, women played significantly less strokes/s, hit fewer aces, won fewer service games and committed more double faults. Although th...