The lower your body fat, the faster you fatigue and also quicker you feel stressed.
don't take me wrong on this comment Fat is a very slow release source of energy and when the protein source gets depleted in your body, the system kicks in to burn fat as a fuel to keep it up. This is the main reason for the fatigue.
Even in strength training having a reasonable amount of fat (Not over, Not under) will keep your joints from being damaged unless you deliberately draining your body from fat for a competition. During this period, you should watch out for the good form and controlled weight to prevent injury.1
This point comes into action in most of heavy weight lifting sports and joints are padded and lubricated by fair amount of stored fat. (and possibly can be a positive). However those athletes benefit from a very strong cardiovascular system and having that extra weight won't be phrased exactly as being "overweight". Excessive fat can be the cause of lot of problems in the body and a good starting point for most issues.
A lower daily fat intake and lower percentage of total
energy from fat were associated with increased injury risk
among competitive female runners. Lower energy intake
and lower energy availability approached, but did not
reach, a significant association with overuse injury in this
study. By documenting these risk factors, it is hoped that
future research will continue to investigate their role in
injury development, thus leading to better strategies to
predict and reduce running injuries in women."1
Additional resources for self-read:
Eating Habits That Reduce Injury Risk
LESS FAT IN DIET LINKED TO INJURY RISK IN RUNNERS
1)Gerlach, Kristen E., et al. "Journal of the International Society of Sports Nutrition." Journal of the International Society of Sports Nutrition 5 (2008):