Physiological responses during submaximal interval swimming training: effects of interval duration

The aim of the present study was to determine the time sustained near <(V)over dot > O-2max in two interval training (IT) swimming sessions comprising 4x400 in (IT4x400) or 16x100 (IT16x100). Elite swimmers (Mean +/- SD age 18 +/- 2 yrs; body mass 66.9 +/- 6.5 kg; swim <(V)over dot > O-2max 55.7 +/- 5.8 ml(.)kg(-1.)min(-1)) completed three experimental sessions at a 50-m indoor pool over a one week period. The first test comprised a 5 x 200-m incremental test to exhaustion for determination of the pulmonary ventilation threshold (VT, m(.)s(-1)), <(V)over dot > O-2max, the velocity associated with <(V)over dot > O-2max [<(V)over dot > O-2max, m(.)s(-1)) and maximum heart rate (HRmax, b(.)min(-1)). The remaining two tests involved the IT4x400 and IT16x100 performed in a randomised order. The two IT sessions where completed at a velocity representing 25% of the difference between the VT and the <(V)over dot > O-2max (Delta 25%) and in the same work to rest ratio. During the IT sessions <(V)over dot > O-2 as well as HR were measured. The duration (s) > 90% <(V)over dot > O-2max, also the duration (s) >90% HRmax, were not significantly different in the IT16x100 and IT4x400. However, limits of agreement (LIMAG) analysis demonstrated considerable individual variation in the time > 90% <(V)over dot > O-2max (mean difference +/- 2SD = 222 +/- 819 s) and the time > 90% HRmax (mean difference +/- 2SD = 61 +/- 758 s) between the two IT sessions. This factor deserves further research to establish the characteristics of those athletes which influence the physiological responses in IT of short or longer duration repetitions.