The validity and reliability of intestinal temperature during intermittent running

Purpose: In many sporting and occupational settings, measuring core temperature using invasive methods is not practical. In these circumstances, ingestible temperature sensor capsules are a promising alternative. To date, no researcher has investigated the validity of intestinal temperature (T _int) during free running or examined the between-trial reproducibility of this technique. Therefore, in two investigations, we examined the validity and reliability of T_int during prolonged intermittent shuttle running. Methods: In investigation A, 10 male games players completed 60 min of exercise while their rectal temperature (T_rec) and T ^int were monitored. In investigation B, T_int was measured while nine males undertook two 90-min bouts of exercise, separated by 7 d. Results: A mean systematic bias of -0.15°C (95% CI, 0.10-0.20) was found between T_int and T_rec during exercise. This bias for T_int to record higher temperatures than T_rec was uniform through the range of measurements, such that the exercise-mediated changes in body temperature were similar between methods of measurement. The 95% limits of agreement were found to be ± 0.22°C (95% CI, 0.11-0.33) and correlations were high (r > 0.85), suggesting that random error between methods was acceptably small. In investigation B, the mean change between repeated trials was a negligible 0.01°C (95% CI, -0.02 to 0.05). The within-subjects SD was 0.08°C (95% CI, 0.05-0.15). Random error was uniform through the measurement range and was deemed acceptable on the basis of statistical power calculations. Conclusion: These findings suggest that the test-retest variability of T_int is acceptably small during intermittent shuttle running. The small amount of random measurement error and similar thermal responses to exercise suggest that T_int is as appropriate for use in exercise physiology research as T_rec, provided that the consistent bias between these measurement methods is allowed for.