Comments

The stated purpose of a recent article entitled: “Comparison of critical swimming velocity and velocity at lactate threshold in elite triathletes” [3] was to determine whether critical velocity (Vcrit) in swimming corresponded to the velocity at lactate threshold (V-LT). The authors concluded that 'Vcrit cannot be used as a simple non-invasive alternative in the determination of LT .... as it consistently overestimates the V-LT.'

Parameters analogous to critical velocity do not correspond with lactate threshold in other forms of exercise. In cycling exercise critical power is not equivalent to lactate threshold [5] [7]. Critical power lies above lactate threshold [7], and the two demarcate the upper and lower limits respectively of heavy intensity exercise [4] [7] [11]. I would suggest that a similar relationship may exist in swimming exercise.

Whilst lactate threshold and critical speed are indices of swimming performance [8] [9], they should not be considered as equivalent.

In swimming the use of critical velocity as an index of performance has been advocated over lactate threshold determination because it obviates the requirement for invasive blood sampling, which is unpopular with athletes and their coaches [8] [9], and which requires expensive equipment [9]. As such, the determination of critical velocity represents an alternative, rather than an equivalent to the determination of lactate threshold.

In the study by Martin and Whyte [3] mean blood lactate concentration during swimming at critical velocity (3.0 ± 1.0 mM) was significantly greater (p < 0.05) than the blood lactate concentration at lactate threshold (1.9 ± 0.4 mM). Critical velocity was also reported as being significantly faster (p < 0.05) than the velocity corresponding to lactate threshold [3]. In the light of these results the authors draw the conclusion that Vcrit overestimates V-LT. The results could equally be interpreted as indicating that V-crit represents an intensity above V-LT. This is supported by the finding that critical swimming speed determined in either a pool or flume was significantly faster than the swimming speed corresponding to a blood lactate concentration of 4 mM [8].

Whilst exercise to exhaustion at critical power or speed can theoretically be sustained indefinitely, mean exercise durations have been recorded of 16 minutes during running [6] and 33 minutes during cycling [2]. Although swimming at critical velocity might not be sustained indefinitely [3], it may be sustained over comparable durations. Swimming exercise which results in blood lactate concentrations similar to those predicted at critical power by Martin and Whyte [3], can be well tolerated. This is despite such concentrations being in excess of those measured at lactate threshold [3]. The reported blood lactate concentration at critical power of 3.2 mmol × l^-1 [3] coincides with the mean maximal lactate steady state value, maintained during 1600 m (4 × 400 m) freestyle swims at critical velocity, with minimal rest for blood sampling (30 - 45 s) [10]. Higher absolute values of lactate steady state can be maintained in other sports, e.g. during 30 minutes of cycling (5.4 ± 1.0 mmol × l^-1) and speed skating (6.6 ± 0.9 mmol × l^-1) [1].

In conclusion, the results of published studies [3] [8] [10] seem to support the assertion that critical swimming velocity, similarly to analogous parameters measured in different types of exercise, corresponds with an exercise intensity above lactate threshold. Critical velocity in swimming should not be considered as equivalent to the velocity at lactate threshold, but to provide an alternative index of swimming performance, corresponding to a higher swimming intensity.

Future research might seek to further elucidate the physiological responses to swimming at critical velocity and the duration over which critical velocity can be maintained.

References

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• 3 Martin L, Whyte G P. Comparison of critical swimming velocity and velocity at lactate threshold in elite triathletes.  Int J Sports Med. 2000;  21 336-368
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• 7 Poole D C, Ward S A, Gardner G W, Whipp B J. Metabolic and respiratory profile of the upper limit for prolonged exercise in man.  Ergonomics. 1988;  31 1265-1279
• 8 Wakayoshi K, Ikuta K, Yoshida T, Udo M, Moritani T, Mutoh Y, Miyashita M. Determination and validity of critical velocity as an index of swimming performance in the competitive swimmer.  Eur J Appl Physiol. 1992;  64 153-157
• 9 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
• 10 Wakayoshi K, Yoshida T, Udo M, Harada T, Moritani T, Mutoh Y, Miyashita M. Does critical swimming velocity represents exercise intensity at maximal lactate steady state.  Eur J Appl Physiol. 1993;  66 90-95
• 11 Ward S A. Determinants and limitations of pulmonary gas exchange during exercise. In: Whipp BJ, Sargeant AJ (eds) Physiological Determinants of Exercise Tolerance in Humans. London; Portland Press 1999: 115-134