Does a lot of stress shrink the results of strength training?

Short answer

Yes. People under heavy stress gained less strength over 12 weeks and recovered more slowly in the 4 days after a workout. But the stress hormone was not the culprit: people whose levels rose more right after exercise actually gained slightly more muscle.

Does a lot of stress shrink the results of strength training?
'Stress → cortisol → muscle breakdown' — does this formula hold?
A common belief says stress releases the stress hormone cortisol, which breaks down muscle, so training is pointless. We checked whether stress really reduces training results, and if it does, how.
Stressed people gained less strength
Same class, same 12 weeks, different results
135 people in a weight training class held 2 times a week were followed for 12 weeks. Those with fewer recent stressful life events gained more on their best bench press and squat than those with many. How much support they got from people around them made no difference.
Recovery was slower too
After a hard leg workout, it lagged for 4 days
31 people did 6 heavy sets of leg press, and researchers tracked how fast their strength came back. The more stressed they were, the slower strength returned, both in the first 1 hour and over 4 days (96 hours). Over those 4 days, energy, fatigue and soreness were also worse with more stress.
So is cortisol the culprit?
No — people with bigger spikes gained more muscle
In a study where 56 people did strength training for 12 weeks, those whose cortisol rose more right after exercise actually gained slightly more lean mass (muscle and everything except fat) and thicker muscle fibers. The short hormone spike during training did not eat away at muscle.
Instead, training volume dropped
After mental effort, reps went down
A 2026 analysis that pooled 11 studies with more than 205 people found that when the brain was tired from about 30 minutes of a focus-heavy task or social media on a phone before training, reps and total training volume dropped. The drop was larger in multi-joint lifts like squats and bench presses.
Cardio showed the same pattern
Highly stressed people barely got fitter
44 people did the same cardio training 5 times a week, 40 minutes each, for 2 weeks. Those who said before the start that they had a lot of stress and little mental reserve gained very little or no fitness. The more reserve people reported, the more they improved.
In turn, strength training reduced anxiety
An analysis of 922 people, bigger effect in healthy people
An analysis that pooled 16 papers with 922 people found that those who did strength training had fewer anxiety symptoms than those who didn't exercise. The effect was larger in healthy people without illness. Stress cut into training results, but training itself worked to ease stress.
Bottom line: stress cuts recovery and training volume
The formula breaks at the 'cortisol → muscle breakdown' link
During high-stress periods, people gained less strength and recovered more slowly. The cause was not the hormone rise during training but slower recovery and less training volume. So in a stressful week, leaving more recovery time between workouts, without stopping training, works.