When progress slows, you may try earlier sessions or more exercise. First, check whether you have enough sleep, recovery time and space in your week to support that work.
Too little sleep can affect your mood, alertness, recovery and how hard exercise feels. The effects vary between people and studies. They cannot predict your muscle gain or fat loss.
What the cited testosterone study found
Leproult & Van Cauter, JAMA (2011) studied 10 healthy young men. After three nights with 10-hour bedtimes, participants had eight nights with 5-hour bedtimes in a laboratory. Daytime testosterone measurements were lower during the restricted-sleep condition.
This was a very small, short study without a separate parallel control group, and it measured testosterone rather than muscle gain, fat loss or training results. It does not establish what six hours of sleep will do to every person, nor does it prove that a particular hormone change determines an individual's physique outcome.
Use sleep as one part of the review
Your progress depends on more than gym sessions. Work, illness, childcare, alcohol, travel and sleep problems can affect how you feel and train. Your programme and total training time also matter.
Track how long and how regularly you sleep, along with your performance, soreness and motivation. Record which sessions you complete and how hard they feel. One difficult week may need no change. A repeated drop in performance deserves a review.
How a flexible training week can help
Your plan can include a normal week and a shorter version for busy weeks. You might keep the main exercises but do fewer sets or shorter sessions. Choose changes using your recent progress, rather than a fixed rule after one poor night.
As recovery improves, you can gradually build training back up. Keep your goal while adjusting the plan. One missed session or poor night does not mean failure.
Practical sleep decisions without false certainty
Try to make regular time for enough sleep. Your needs and circumstances matter. Reviewing caffeine, alcohol, light, room comfort and your bedtime routine may help. Speak to an appropriate healthcare professional about ongoing sleep problems, strong daytime sleepiness, loud snoring, breathing pauses or other concerning symptoms.
A coach reviews sleep alongside training, consistency and recovery, then makes suitable changes to the plan. Coaching does not diagnose sleep disorders or promise changes in hormones or body shape.
If you want a training structure with a realistic normal-week and compressed-week option, the free starter guide explains the framework, or you can apply for coaching.