Many experts warn you to watch out for too long a workout length but miss the real issue at hand.
The lore teaches you to avoid any length over an hour. Once you pass an hour, things changes right away. Horrible events occur once you go beyond just a millisecond over 60 minutes, so they say.
Cortisol
The levels of a stress hormone called cortisol will increase. Although cortisol plays a vital role to regulate many factors, you need to avoid generating too much for get your best results from lifting. Cortisol is catabolic, meaning it can break down muscle.
The ratio of testosterone, a growth hormone, to cortisol gets attention from exercise scientists since it may show the status of the body. A boost in testosterone, a drop in cortisol, or a combination could indicate if muscle growth is occurring.
Its usefulness has been questioned though. Hormone analysis only presents a single piece of a complex puzzle. Although we know that steroids work by elevating growth hormones at all times, we know less about the effect of normal fluctuations in a natural trainee.
Bodybuilding with many sets and exercises, moderate reps, and short rest periods may boost cortisol but some research states it also ups testosterone.
Perhaps the net effect leads to neutral.
A Sensible Point of View
Some try to cram as many exercises, sets, and advanced techniques within an hour as they can. They believe by staying below it, the stress from exercise could never exceed their limits.
This is wrong; if you performed a regimen of many negative reps, you could need months to recover for work done within a matter of minutes. Too much exercise overall will overtrain you.
Workout length only matters to the degree that more time allows for more exercise. If you follow my advice to perform 1-2 warm-up sets, focus on just three strength training exercises, use a single work set, use the right rest periods, and add intervals for cardio, the length means nothing since the amount of exercise is so low to increase cortisol too much. A high volume is the real reason that long workouts can harm your progress.
Avoid Analyzing Workout Length
Use your limited recovery ability as wisely as possible, and as little as possible in line with the actual requirements for producing the results.
– Arthur Jones
Perhaps at first suggested as just a rule of thumb, many have abused the hour limit to their harm. Ignore workout length. Instead focus on making progress with the least amount of exercise you need to achieve your goal.