Too much of a good thing?
For the past 25 years, one of my favorite things is outdoor exercise soon after I wake up. For the last 15 years, my regular form of this exercise is a run. Not a fast run. Not a hill repeat run. Not an interval run. Just a meditative, breath fresh air, build a bit of sweat run. And I am absolutely paranoid that my decisions about how much and how intensely I exercise aside from this morning routine could prevent me from doing this activity. I do not want to risk becoming demotivated or injured.
When I started high intensity interval training, and learned more about the benefits, I contemplated fitting these sessions into my schedule as much as possible. It was only 30 minutes and the feeling after was such an energy rush! In less than a month I realized there could be too much of a good thing as I started to feel the effects. I was not excited about my morning run, my knees ached, and I was less than my usual bubbly, charming self.
So, I started to research the guidelines for professional athletes created by their trainers and medical staff. Each sport has a specific maximum number of minutes in the highest intensity zone of 90-100% heart rate max, typically based upon total training or game minutes and modified throughout the season. It is interesting that there are not similar recommendations for active adults who are not athletes.
More often than not, we discuss how to encourage a regular exercise routine of any intensity as the majority of the global population is not active. Yet, the less common scenarios of too much activity or too much intensity, without proper recovery, lead to a buildup of stress that can become harmful.
One of the primary stress hormones is cortisol. In terms of function, cortisol can help control blood sugar, regulate metabolism and reduce inflammation. Short term elevation of cortisol has positive effects such as building, adapting and repairing muscle. Long term elevation has negative effects such as intense fatigue, joint pain, and mood disturbance potentially developing into a condition termed overreaching.
So how much high intensity training per week triggers the positive effects and not the negative? We completed a study to help define this ratio by collecting data on adults who were currently exceeding the weekly physical activity guidelines. In fact, the mean exercise time was eight hours per week! The participants simply continued their typical training routine for three weeks and recorded their exercise heart rate with a chest transmitter.
With respect to intensity, the participants naturally divided into the following three groups based upon total minutes training above 90% heart rate max; (1) less than 25 minutes per week, (2) between 30-40 minutes per week, and (3) greater than 45 minutes per week. At the end of the three weeks, we subjected the participants to an extreme experimental session of two high intensity interval training sessions separated by only 4 hours. (DO NOT TRY THIS AT HOME!!!) We measured their cortisol before each workout, immediately after, and 30 minutes after. The data demonstrated that the group who completed more than 45 minutes per week in the highest zone had an elevated resting cortisol and did not demonstrate the short terms elevations that are ideal for improving health and fitness. These individuals were not benefiting from the positive effects of cortisol and were potentially doing more harm. So yes, you can do too much of a good thing.
What is the simple, practical application of all this biochemistry?!?!
STRAP IT ON!!! (teehee*)
* = shout out to Josh Keenum
If you are serious about maximizing your cardiovascular fitness, invest in and strap on a chest transmitter. Record your exercise heart rate for a full, typical training week. Add your total exercise time in a week (TET) and add your total time in 90-100% HR max in a week (TT90). Next, complete the following calculation:
(TT90/TET) x 100 = percent time above 90%.
The ideal percentage range is 4-9%… what is your number?