In recent years, there has been a tendency away from measuring bodyweight in the general population and within sport. While it is true that obsessing with the number on the scale can be detrimental to mental health and overall health by extension, there are several reasons why bodyweight matters in sport.
In this article we will use the terms bodyweight, weight and mass interchangeably, with full knowledge that mass is the correct term.
Why bodyweight matters in sport
Weight and body fat percentage are not necessarily proxies for exercise performance. However, this does not mean getting on the scales is useless. Below are some of the several aspects of sport where bodyweight is important.
Weight category sports
In many sports competition happens within set weight categories. Examples include combat disciplines (e.g. boxing, Brazilian jiu jitsu, judo, mixed martial arts), strength sports (Olympic weightlifting, powerlifting), horse racing and lightweight rowing.
Knowing and monitoring the athlete’s bodyweight is important for determining at which category they should compete and which weight cutting strategies to utilise. Weight has to be monitored during the whole training camp at least until weigh ins.
The estimated energy requirements for an individual can be calculated using their bodyweight (and other parameters, such as gender and age). More accurate calculations can be made by using lean body mass, but weight-based calculations are accurate enough for most purposes.
The actual energy requirements for an individual do require measuring bodyweight in addition to energy intake. By monitoring changes in bodyweight and total energy intake, we can conclude how much energy the individual needs to maintain a certain weight, as well as what adjustments to make for weight loss or gain.
Carbohydrate and protein requirements
Carbohydrate and protein requirements are, in most cases, expressed as grams per kilogram of bodyweight (or ounces per pound of bodyweight).
Carbohydrate is the main source of fuel in moderate to intense exercise. It is stored as glycogen in muscle and liver, therefore recovery from exercise involves the replenishment of used stores during exercise via carbohydrate intake. The ability to use and store carbohydrate likely depend on body mass. One exception is endurance exercise or team sports that are highly glycolytic, in which carbohydrate requirements are expressed in grams per hour. This is because the limiting factor is the rate of carbohydrate metabolism, which is independent of bodyweight.
Protein is required for muscle growth and development, making it important for muscle function, strength and recovery. Protein requirements are directly dependent on the athlete’s muscle mass, and by proxy, body weight.
Fluid in the body is present within cells (intracellular) and around cells (extracellular). It makes sense that larger bodies have larger fluid content, and therefore larger requirements. Fluid requirements can be expressed in millilitres per kilogram of bodyweight (or ounces per pound of bodyweight).
The scales are also a great tool for accurately determining post-exercise fluid needs for rehydration. This is achieved by measuring bodyweight before and after exercise to account for sweat losses, factoring in how much fluid was drank during exercise, and adding 25-50% of the net fluid losses.
Some performance measures, such as power-to-weight ratio used in cycling, are expressed relative to bodyweight to allow for comparison between athletes.
Likewise, there are multiple performance standards for lifts (e.g. squat, deadlift, bench press, snatch, clean and jerk) which are based on body weight. These allow athletes, coaches and researchers to assess strength performance and progress. These standards may be expressed in times bodyweight (e.g. 1.5x bodyweight) or as tables by weight such as those found here.
While some supplements can be taken at generic doses with no detriment to their effects, some are most effective when taken at doses based on bodyweight. Examples include caffeine, creatine and bicarbonate, all of which are well-studied ergogenic aids.
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