Final answer:
Exercising too close to bedtime can make falling asleep more difficult due to increased alertness and endorphin levels, although exercising earlier in the day generally improves sleep quality.
Step-by-step explanation:
Concerning the effect of exercising too close to bedtime on sleep, research shows that while physical exercise generally improves sleep quality and aids in managing sleep disorders like insomnia, there's a caveat. Engaging in heavy exercise shortly before going to bed may make falling asleep more difficult. This is because intense physical activity can increase alertness and endorphin levels, which might delay sleep. However, exercise performed four to eight hours before bedtime can yield sleep benefits and is often advised for those with sleeping difficulties.
To summarize the effects, the optimum time to exercise for better sleep is earlier in the day, and exercising too late, especially if it is vigorous, can interfere with sleep. This is why therapists often recommend clients with insomnia to exercise during the day but avoid heavy workouts close to bedtime.