Many athletes notice that hard sessions feel worse after a draining day. Research on mental fatigue has explored this, although the size and consistency of the effect are debated.
What studies have suggested:
Prolonged demanding cognitive tasks before exercise have been linked with higher perceived effort and reduced endurance in some experiments
The physical capacity seems largely unchanged; the effect seems to be mostly on how hard the effort feels
Some newer studies and reviews have found smaller or less consistent effects than early research
Decision-making and skill in team sports may also be affected
A practical approach for busy athletes: where possible, put key sessions on lower-stress days or earlier in the day, and keep easy or technique sessions for the days that are mentally heavy.
If you must train hard after a long day, a proper meal, a short break away from screens and a longer warm-up can help.