Response to Chaen and Trapellieni re: “Shortening Work-Rest Durations Reduces Physiological and Perceptual Load During Uphill Walking in Simulated Cold High-Altitude Conditions,” by Fornasiero et al.

This letter is in response to the letter by Chaen and Trapellieni. We appreciate the interest in our article, and we would like to reply point by point to each issue raised by the authors.

First, as the authors correctly assumed, the treadmill kept running throughout the entire protocol. This clearly limited the amount of work needed for accelerating and decelerating the body at the start and at the end of each bout of exercise. The decision of keeping the treadmill running was not taken to avoid introducing acceleration/deceleration phases, but indeed to avoid some issues related to the time required for stopping and running again the treadmill. However, we would like to point out that, even in real-world situations, in the case of uphill walking the deceleration phases happen with negligible muscular work and, therefore, they do not affect metabolic power (Minetti et al., 1993). Moreover, if we estimated the mechanical work for each acceleration, considering the increment of kinematic energy and by taking the average speed, this would be equal to 0.1012 J/kg. Therefore, the total mechanical work for the acceleration phases would be of about 1 J/kg for the LONG protocol (10 accelerations) and 2 J/kg for the SHORT protocol (20 accelerations). This amount of mechanical work is negligible if compared with the total mechanical work done against gravity, which was indeed, on average, 3,963 J/kg. For this reason, even if we had included accelerations/decelerations phases, these would not have accounted for any dissimilar heart rate responses when comparing the two protocols of uphill walking matched for total work.

Second, a randomized crossover design was indeed the design we adopted in the study, which, by chance, further resulted in a balanced allocation of the subjects between the two conditions (i.e., half of the participants started with the SHORT protocol, whereas the other half with the LONG protocol). Therefore, we can rule out any possible “sequence” effect on the observed results.

Third, we agree on the value of involving female subjects, but as the authors certainly know, it is not always feasible to conduct research studies with complex designs aimed at producing independent observations for women or at pointing out any possible gender effect in the investigated variables. Unfortunately, this is a common issue. Indeed a recent study showed that, across some major sports and exercise medicine journals, the percentage of studies including both female and male participants ranged between 53% and 78% and, among these, the percentage of female participants per article ranged from 35% to 37% (Costello et al., 2014). Even though we believe this does not affect the validity of our observations, we recommend being cautious when generalizing the present results to female subjects. Further research seems to be needed to better characterize the impact of different protocols of exercise on physiological responses and cardiac autonomic activity in women at high altitude, with special attention to the existing influence of ovarian cycle phases and menopause on these responses (Richalet et al., 2020). We thank the authors for helping us better underline this latter aspect.