Across rowing, much of the recent work and questions surrounding the phsyiological training for our sport have involved looking at the distribution of various intensities needed to drive adaptation in athletes, and which mixture of easy and hard work yields the best results.

Arguably the most attention in recent years has been focused on the idea of polarized training, that is the idea that you do a lot of really easy work, and then a small proportion of really hard work, taking care that the lower intensity efforts truly stay "easy" and the harder efforts are taking place at 80% effort and higher.

Recently, the buzzword has been "Zone 2," which is the idea that much of your steady aerobic work is done at 60-70% of your maximum heart rate (or 48-52% of your 2K score expressed in watts). The idea is that working at this lower intensity allows an athlete to increase volume without overtraining, train the body to rely on stored fat for fuel (instead of relying predominantly on stored carbohydrates, which is the case in higher intensity exercise), and, because the intensity is lower, the body's overall response to the stress of exercise is lower--the body is able to recover more quickly.

In a blog post last week, physiologist and data scientist Marco Altini examined Low-intensity exercise and the stress response, and came to a few surprising conclusions.

Altini, who is the founder of HRV4Training and an advisor at Oura (manufacturers of the Oura ring), looked at the effects of varying intensities of exercise on athlete's HRV (heart rate variability, see here for a more extensive definition) and the levels of the stress hormone Cortisol circulating in the body (Cortisol is released by the body in response to mental and physical strain, including exercise).

Altini examined the data from various studies, including one (by E.E. Hill, et al¹) that found that "while exercising at 60 or 80% of VO2max led to increased circulating cortisol levels, exercising at 40% of VO2max led to a reduction."

In another study, by Stephen Seiler² (whose work is familiar to many who keep abreast of the latest work in exercise physiology), the scientists found that HRV was lowered after moderate- or high-intensity exercise, but increased after low-intensity exercise--the implication being that exercising at a lower intensity could actually reduce the stress response in the body.

For rowing, the implications could not only be to program more lower-intensity sessions into a given training plan, but you could also look at adding lower-intensity components to strenuous sessions (ie. a longer cool-down after a hard practice) that might prove beneficial.

In other words, don't skimp on the low intensity work, and don't skip the cool-down--both can help you in the long term!

¹ Hill, E. E., et al. "Exercise and circulating cortisol levels: the intensity threshold effect." Journal of endocrinological investigation 31 (2008): 587-591

² Seiler, S., Haugen, O. and Kuffel, E., 2007. Autonomic recovery after exercise in trained athletes: intensity and duration effects. Medicine and science in sports and exercise, 39(8), p.1366