Reply to Comments from S. A. Taylor

We wish to thank Mr. Taylor for his supportive comments to our recent work comparing critical swimming velocity (Vcrit) and velocity at lactate threshold (V-LT) in elite triathletes [2]. Mr. Taylor's endorsement of the two key points, 1) that Vcrit and V-LT are different with regard to the physiological responses that they elicit, and 2) that future research needs to further clarify the exact physiological responses to exercising at Vcrit, will ensure that future research is undertaken in this area.

Since statistical analysis indicates that a strong relationship exists between Vcrit and V-LT, r = 0.91 (P < 0.05) and coefficient of variation (CV) = 3.5 %, some individual's may be tempted to utilise Vcrit as a direct alternative to V-LT. However, this may be somewhat erroneous. The calculation of Limits of Agreement [1] indicates that with the same data there is a lack of agreement between the two variables (0.08 ± 0.08 m × s^-1). Although this may seem comparatively small, at the upper end of these limits the time required to complete 300 m at Vcrit may be as much as 30 seconds less than for the calculated V-LT. Such an increase in exercise intensity over time may lead to a detriment in performance rather than an improvement, particularly in the triathlon group that were studied. It is clear, therefore, that in terms of exercise prescription of specific training intensities Vcrit does not provide an acceptable alternative to V-LT. There is potential for Vcrit to be used as a monitoring tool to indicate general improvements in aerobic fitness without the need for invasive testing if future research demonstrates that improvements in V-LT will also lead to improvements in Vcrit, and vice versa.

Finally we feel that it is important to reiterate that this work was completed on elite triathletes and not on competitive swimmers. Clearly the physiological requirements of triathlon are very different from those of competitive swimming. In swimmers for exercise prescription V-4 mM is often used as the most relevant point on the lactate curve and hence Vcrit is potentially an acceptable, non-invasive alternative to the lactate threshold test [4] [5]. For triathletes performing at an optimal pace without creating fatigue that will hinder performance in the subsequent discipline is crucial to success [3] and consequently the measurement of Vcrit for exercise prescription may be inappropriate, as previously identified.

The impact of Vcrit on performance and its response to training and detraining needs to be clearly identified before its use as a simple non-invasive test for the sports coach and practitioner can be used with confidence.

References

• 1 Bland J M, Altman D G. Statistical methods for assessing agreement between two methods of clinical measurement.  Lancet. 1986;  1 307-310
• 2 Martin L, Whyte G P. Comparison of critical swimming velocity and velocity at lactate threshold in elite triathletes.  Int J Sports Med. 2000;  21 366-368
• 3 O'Toole M L, Douglas P S. Applied physiology of triathlon.  Sports Med. 1995;  19 251-267
• 4 Wakayoshi K, Yoshida T, Udo M, Kasai T, Moritani T, Mutoh Y, Miyashita M. A simple method for determining critical speed as swimming fatigue threshold in competitive swimming.  Int J Sports Med. 1992;  13 367-371
• 5 Wakayoshi K, Yoshida T, Udo M, Harada T, Moritani T, Mutoh Y, Miyashita M. Does critical swimming velocity represent exercise intensity at maximal lactate steady state?.  Eur J Appl Physiol. 1993;  66 90-95