In some sports, body fat mass is not, up to a point, a determinant of performance. These are mainly stationary sports or sports with only casual movement requirements. Archery, shooting, bowling, golf to a lesser extent, and quite a few others that can be described as "sports" are examples. However, even in these sports, excess body fat may imply reduced fitness and endurance, which may reduce overall performance in lengthy competition formats.
In sports like endurance running and cycling, low body fat levels (<7% men and <12% women are common), and modest muscle mass are usually considered advantageous because this body composition increases power-to-weight ratio and is likely to increase body heat dissipation. Bodybuilders will aim for even lower body fat percentages.
Swimmers are somewhat paradoxical because even with similar energy expenditures to some non-water sports athletes, they tend to carry more fat without impairing efficiency, perhaps by improving flotation. Even so, excessive body fat will impair swimming performance. It’s up to individual coaches and advisers to judge the requirements for body fat in various events in swimming.
In contact sports like NFL and rugby, certain levels of body fat in particular team positions may improve performance, while in others it will impair performance. Players who are big-tackling defensive players generally require bulk and perhaps more fat to repel tackles and protect themselves from injury. Attacking, offensive backs often need to be fast and mobile with the ability to change pace and swerve quickly. Body fat generally should be below 10% in elite male backs and below 15% in the big defensive men. No doubt exceptions exist. Baseball players will get away with fat levels <10%-15% but male gymnasts and basketball players generally need to be lower. These are just examples and it is important for coaches and managers to be flexible in proscribing acceptable body fat levels. Adjustment in accordance with genetics and performances are prudent.
Muscle bulk is not necessarily synonymous with strength -- or power for that matter: it depends on the explosiveness and duration of the activity and the training undertaken. Power and strength for sprinting or powerlifting is obviously not the same as power for the marathon or riding the Tour de France.
Whatever the relationship between muscle bulk and athletic performance in general, it’s certain that for many ball sports in particular, timing, speed and technical skills are the predominant requirements. Finding the right balance of muscle bulk for optimal performance in any particular sport is something of an arcane science.
Too Heavy or Too Light
The consequences of being above optimum weight are equaled by the potential disabilities of under-eating and being under ideal weight. In disordered eating in women athletes, there are three consequences: disrupted periods, hormone dysregulation and bone density irregularities – the female triad.
Even with non-athlete weight-loss programs, eating disorders that result in loss of too much body fat can induce hormone irregularities and chronic illness, especially in women. The stick-thin look so sought after in some glamour circles, and propagated by many women celebrities, could be a dangerous target for those with a more naturally robust body shape.
Read other articles in the Sports Nutrition series:
- Eating and Drinking for Energy in Exercise and Sports
- Carbohydrates for Energy in Sports and Exercise
- How Much Protein for Athletes and Exercisers
- Ideal Body Fat Percentage for Athletes and Active People