One of the most interesting aspects of sport physiology is the inter-individual differences in training responses observed in athletes that are exposed to standardized programs. You can put a team of athletes through the same conditioning program and end up with some athletes showing no change or a tremendous increase in fitness (~40% at post-testing). Why is there such a big discrepancy in training adaptations if all of the athletes are given the same training stimulus?
It turns out that genetics play a huge role in how an individual will adapt to training. Over 50% of the variance in individual training responses is explained by genetics. Since there isn’t much that one can do about their genetics, what other factors should we be managing to optimize training effects with our athletes?
A very interesting study that was published in 2012 in Frontiers in Physiology, and seems to have flown under the radar, evaluated the effects of perceived stress levels on fitness improvements in 44 healthy subjects. Perceived stress levels and fitness markers were evaluated before and after a two week conditioning program. The program was standardized with 5 sessions per week at a duration of 40 minutes per session at an intensity corresponding to 75% of maximum heart rate.
The results showed that mean VO2max values significantly improved following the two week training protocol. Baseline stress levels were significantly correlated with changes in fitness when measured as a group (r = 0.45) and when separated by gender (males: r = 0.43; females: r = 0.44).
Though these correlation coefficients are only moderate, it provides an important piece of information pertaining to training adaptations. Roughly 20% of the variance in VO2max changes was explained by baseline levels of perceived stress. The authors speculate that elevated cortisol levels may have affected individuals’ capacities to adapt to the training stimulus. Future research will need to measure cortisol and androgens to see how these variables effect training responses. The take home message here is to monitor and manage stress levels in athletes to make them more adaptable to training.
Ruuska, P. S., Hautala, A. J., Kiviniemi, A. M., Mäkikallio, T. H., & Tulppo, M. P. (2012). Self-Rated Mental Stress and Exercise Training Response in Healthy Subjects. Frontiers in Physiology, 3, 51. doi:10.3389/fphys.2012.00051