Exercise is a stress on the body that impacts cortisol levels in much the same way as a looming work deadline or lack of sleep. “These stresses can deplete our energy and ultimately negatively impact our performance when it comes to training,” says Matthew N. Berenc, CSCS, the director of education at the Equinox Fitness Training Institute.
The solution: ‘Flexible training’—laying out weekly or monthly sessions, then choosing which one you’re going to do based on energy levels or daily ‘readiness’—can aid long-term progress while accommodating the ebbs and flows of life, says Michael C. Zourdos, Ph.D., CSCS, an associate professor of exercise science at Florida Atlantic University.
For example, maybe you’d aim to train three times a week with one day as a high-intensity day, another as a low-intensity day, and a third as a moderate-intensity day. Or if you’re a runner, perhaps you slate one speed work day, one strength-training day, two tempo runs, and one long run. (You would need to determine which runs/workouts are more/less taxing, perhaps rating them on a scale of one to five.) Then, the goal each week is to complete one of each day of the program on any day of the week.
“Essentially, you pick how hard you are going to push yourself based on how ready you feel,” says Berenc. “You aren’t skipping a day, just rearranging the order. This helps with consistency of training and ensures you can give it your all when you do complete a harder workout.” While this approach can be applied permanently, it can be especially useful during stressful times of year like the holiday season.
In a lab setting, picking the right session for the right day is formulaic. A testosterone-to-cortisol ratio may be able to assess daily readiness and predict performance, notes Zourdos. Everyday athletes can instead use the following more practical process.
Analyze the day(s) surrounding training.
Look at factors like how well you slept, ate, pushed yourself in the gym, and performed at work, suggests Berenc. Being familiar with your body and what it needs comes into play here, too. “The better you know yourself and have a sense of how you feel, the more you will be able to distinguish between true fatigue and just nerves,” he says. Beware not to fully rely on feelings like tiredness or anxiousness; they don’t always pose a problem for physical performance, says Zourdos.
Make a decision post-warm-up.
You might feel slow upon arrival, but getting your blood flowing could leave you ready for a challenging session, according to Zourdos. He suggests using a rating of perceived exertion (RPE) to judge readiness. If, toward the end of a warm-up, your RPE is low (you could easily do more work), choose a tougher day, he says. If RPE is high (you’re gassed), choose a lighter day.
Check your resting heart rate.
Says Berenc: “If your resting heart rate is normally 60 beats per minute but today it is 70 beats per minute, that is a sign you may not be recovered from prior stresses and it would be better to go with easier training.” Do a few tests for accuracy and make sure you’re taking your measurements at the same time of day with little to no activity a few minutes prior.
Flexible training applies both ways. “While we often use it to decide if we should go with a lower-intensity day, we can also use it to prioritize high-intensity when the program calls for low,” says Berenc. If you feel ready to push yourself, swap an easier day for a harder one.
And if you’re constantly skipping ‘hard’ days, it could be time to re-analyze your program, he says. “It may be a little too aggressive and causing you to skip days because you haven’t fully recovered yet.” The fix could be as simple as tweaking some of the weights or changing a few exercises.