PHYSIOLOGICAL RESPONSES AND STROKE-PARAMETER CHANGES DURING INTERVAL SWIMMING IN DIFFERENT AGE-GROUP FEMALE SWIMMERS GEORGIOS TSALIS, 1 ARGYRIS G. TOUBEKIS, 2 DIMITRA MICHAILIDOU, 3 VASSILIOS GOURGOULIS, 4 HELEN DOUDA, 4 AND SAVVAS P. TOKMAKIDIS 4 1 Aristotle University, Thessaloniki, Greece; 2 Faculty of Physical Education and Sport Science, Department of Aquatics, Kapodistrian University of Athens, Athens, Greece; 3 Department of Physical Education and Sport Science, Thessaloniki, Aristotle University, Greece; and 4 Department of Physical Education and Sport Science, Democritus University of Thrace, Komotini, Greece ABSTRACT Tsalis, G, Toubekis, AG, Michailidou, D, Gourgoulis, V, Douda, H, and Tokmakidis, SP. Physiological responses and stroke- parameter changes during interval swimming in different age-group female swimmers. J Strength Cond Res 26(12): 3312–3319, 2012—The purpose of the study was to examine the physiological responses, the stroke-parameter changes, and the ability to sustain a velocity corresponding to critical velocity (CV) during interval swimming on female swimmers of different age groups. Eight children (C; age: 10.4 6 0.6 years), 11 young (Y; age: 13.1 6 0.4 years), and 7 adults (A; age: 19.9 6 4.6 years) swam all-out efforts of 50, 100, 200, 400 m for CV and critical stroke rate (CSR) calculation. Subsequently, the swimmers performed an interval training set of 5 3 300-m (C) and 5 3 400-m repetitions (Y and A) at a velocity correspond- ing to CV. The CV was higher in the Y and A compared with the C group (C: 0.962 6 0.05, Y: 1.168 6 0.09, A: 1.217 6 0.05 ms 21 , p , 0.05). The velocity of 5 3 300 and 5 3 400 m was not different compared with CV (C: 100 6 2%, Y: 98 6 3%, A: 98 6 3% of CV, p . 0.05). The blood lactate concentration was similar between groups and was maintained steady within each group (C: 4.5 6 1.4, Y: 4.9 6 1.4, A: 3.9 6 1.3 mmolL 21 , p . 0.05). Heart rate was higher in the C and Y compared with the A group during the last 100 m of each repetition (p , 0.05). Stroke rate remained unchanged during the repetitions and was similar between groups and no different to the CSR (p . 0.05). Stroke length of the fifth repetition was 4.5 6 4.0% shorter compared with the second repetition in the Y and 5.3 6 2.0% shorter compared with the first repetition in the A group (p , 0.05). During the 28- to 31-minute duration intermittent swimming, children and young and adult female swimmers were able to sustain CV with a steady and similar blood lactate concentration. Decreased stroke length may indicate an earlier fatigue in young and adult swimmers. KEY WORDS critical velocity, critical stroke rate, lactate steady state, swimming training INTRODUCTION T he identification and application of the appropriate pace for swimming training is based on regular testing during a training season. Several valid tests may be used for testing swimmers, including pro- gressively increasing intensity or repeated 30-minute efforts of constant intensity and blood sampling for the lactate thresh- old determination or the maximum lactate steady-state calculation (MLSS) (9,20). Maximum intensity efforts of middle- and long-distance swimming may be also used for critical velocity (CV) calculation (i.e., 200–800 m) (10,31) suggesting that it may subsequently be effectively used for training pace prescription (8,27). To use CV for training pace adjustment, it is critical to identify the physiological responses at this intensity (14,23,25) and locate it within the exercise intensity domains. While examining this issue, most of the studies have used male swimmers, and there is only limited evidence concerning the metabolic response differences between age-group and adult female swimmers at a velocity corresponding to CV (15,30). Children and young age-group male swimmers demonstrated different metabolic responses when swimming around CV, providing evidence that children compared with young or adult swimmers, exercise at a different intensity domain when swimming at CV (14). An age-dependent metabolic response and fatigue profile has been reported which may also be altered by the gender (12,13,21). Further- more, any difference in metabolic responses may interact with temporal swimming parameters such as stroke rate (SR) and stroke length (SL) (9). Maintenance or improvement of technical parameters such as SR and SL is a valuable issue during endurance swimming Address correspondence to Argyris G. Toubekis, atoubekis@phed.uoa.gr. 26(12)/3312–3319 Journal of Strength and Conditioning Research Ó 2012 National Strength and Conditioning Association 3312 Journal of Strength and Conditioning Research the TM Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.