Body composition is often discussed as though there is a simple relationship between physique and performance.
Athletes are told they should be leaner, lighter or more muscular, with the implication that changing body composition will automatically improve performance.
The scientific literature does not support such a straightforward conclusion.
Body composition is associated with athletic performance in some sporting contexts, but the strength and direction of that relationship vary according to the sport, the event, the athlete and the performance outcome being measured (Mathisen et al., 2023; Kettunen et al., 2025).
More importantly, much of the literature describes associations between body composition and performance rather than demonstrating that deliberately changing body composition causes an improvement in performance (Mathisen et al., 2023).
That distinction is important.
So, what does the evidence actually tell us?
What is body composition?
Body composition refers to the different components that make up total body mass. In sports research, this commonly includes fat mass, fat-free mass and, where measurement methods allow, skeletal muscle and bone mineral components (Pettersson et al., 2024).
This matters because two athletes can have the same body mass but substantially different amounts of fat and lean tissue.
Likewise, athletes competing in different sports can have very different body-composition profiles while achieving high levels of performance.
Recent research comparing endurance, strength and intermittent-sport athletes found distinct body-composition profiles between sporting disciplines, reinforcing the importance of considering body composition in relation to the demands of the sport rather than treating one physique as universally optimal (Sánchez-Oliver et al., 2025).
The basic question is therefore not simply:
“How much does the athlete weigh?”
It is:
“What does that body mass consist of, and how does it relate to the demands of the sport?”
Why might body composition influence performance?
There are several reasons why researchers have investigated body composition as a potential determinant of performance.
In sports where athletes repeatedly move their own body mass, body mass and its composition may influence the physical demands of movement. In strength and power sports, lean tissue is relevant because skeletal muscle contributes to force production. These relationships mean that the balance between fat mass, lean mass and total body mass can be relevant to different sporting tasks (Pettersson et al., 2024; Mathisen et al., 2023).
However, the importance of these relationships differs considerably between sports.
For example, the demands placed on body mass during endurance running are different from those experienced by a rugby forward or an Olympic weightlifter. Consequently, the body composition associated with elite performance in one sport should not automatically be considered appropriate for another (Mathisen et al., 2023; Delany et al., 2025).
Is lower body fat associated with better performance?
There is evidence that lower levels of fat mass are associated with better performance in some endurance populations.
A critical review of 29 longitudinal, prospective and intervention studies found that higher body-fat measures were negatively associated with performance in prolonged endurance events. However, the review also found that training variables and previous performance were sometimes equally or more important predictors of subsequent performance (Mathisen et al., 2023).
More recent research supports the existence of an association, while also demonstrating why it should not be interpreted too simplistically.
Kettunen et al. (2025) studied 52 elite endurance athletes and examined changes in body mass and body composition during different stages of the training season alongside endurance performance. The study investigated whether changes in body composition were associated with changes in performance rather than simply comparing athletes at one point in time.
This type of longitudinal approach is useful because it provides more information than a simple cross-sectional comparison.
However, it still does not establish that deliberately reducing fat mass will improve performance in every athlete.
That distinction remains important.
Lower body fat is not automatically better
The evidence does not identify a universal body-fat percentage at which athletes become optimally conditioned for performance.
In fact, the critical review by Mathisen et al. (2023) found no unique body-composition cut-off that could be used to signify a performance advantage.
Research in volleyball provides a useful sport-specific example. A systematic review and meta-analysis found that body-fat levels differed according to sex but were not clearly associated with competitive level, leading the authors to conclude that relative body fat did not appear to be a strong indicator of performance level in competitive volleyball players (González-Ravé et al., 2023).
This is an important counterpoint to the idea that lower body fat necessarily means better performance.
The relationship may exist in some sporting contexts without being a universal predictor of sporting ability.
Endurance sports may be different
The evidence for a relationship between body composition and performance is arguably strongest in endurance sports.
A 2024 observational study of 53 elite athletics competitors found that endurance athletes and power athletes displayed different body-composition profiles. Power athletes had greater body mass and fat-free mass, while endurance and power athletes showed different seasonal patterns of lean-mass changes (Pettersson et al., 2024).
Importantly, the researchers did not observe significant reductions in whole-body fat mass or percentage body fat from the off-season to the in-season period across the athlete groups (Pettersson et al., 2024).
This is an interesting finding because it demonstrates that elite athletes do not necessarily need to become progressively leaner during the transition into competition.
In the same study, increases in lean mass were observed particularly among power athletes, while male endurance athletes also demonstrated an increase in lean mass across the season (Pettersson et al., 2024).
This provides a useful reminder that athletic development does not always involve losing fat mass.
What about muscle mass?
The evidence for lean mass is also important.
A critical review of body composition and performance found that increases in muscle mass were associated with favourable performance outcomes across a broader range of sports than the evidence for low body fat (Mathisen et al., 2023).
However, it is important not to confuse an association between muscle mass and performance with proof that increasing muscle mass itself causes the improvement.
Resistance training provides a good example.
A 2024 systematic review examining resistance training in elite athletes reported improvements in sport-specific performance outcomes following resistance-training interventions (Makaruk et al., 2024).
These improvements can occur alongside changes in muscle size, but resistance training produces numerous adaptations beyond hypertrophy, including changes in neural function, force production and power. Consequently, a performance improvement following resistance training cannot automatically be attributed to an increase in muscle mass alone (Makaruk et al., 2024).
This distinction matters when interpreting body-composition research.
Muscle mass may contribute to performance without being the sole cause of performance improvement.
More muscle is not necessarily better
It is tempting to assume that if muscle mass can contribute to performance, increasing it must always be beneficial.
The evidence does not support that conclusion.
Elite athletes competing in different events demonstrate different combinations of lean mass and fat mass. In the 2024 longitudinal athletics study, power athletes had greater fat-free mass than endurance athletes, while both groups demonstrated seasonal changes in lean mass (Pettersson et al., 2024).
This suggests that the amount of lean mass required is influenced by the sporting event.
A further consideration is that additional muscle also contributes to total body mass. Whether that additional mass is advantageous depends on the performance task and whether the increase in force or power sufficiently offsets any consequences associated with carrying additional mass (Mathisen et al., 2023).
Therefore, the more useful concept is not simply “more muscle”, but “appropriate functional lean mass.”
Strength and muscle mass are related — but not identical
Recent research also highlights why muscle mass should not be treated as a direct substitute for strength.
A 2025 study in collegiate athletes examined associations between muscle-mass measures obtained using DXA, bioelectrical impedance analysis and deuterated creatine dilution, and measures of muscular strength (Wilson et al., 2025).
The study demonstrates that different approaches to estimating muscle mass can provide different information and that muscle mass is related to, but should not simply be equated with, muscular strength (Wilson et al., 2025).
This has an important practical implication.
If the performance outcome of interest is strength, then strength should actually be measured.
If the outcome is sprinting, sprinting should be measured.
If the outcome is jumping, jumping should be measured.
Body composition may help explain performance characteristics, but it should not replace direct performance assessment.
Body composition and football
Football provides a particularly interesting example because players require a combination of physical qualities rather than one dominant attribute.
Professional footballers need to perform high-intensity actions alongside prolonged intermittent activity, with physical demands varying according to position and playing role (Sebastiá-Rico et al., 2023a).
A systematic review and meta-analysis examining professional male footballers found significant positional differences in several measures, including body mass, muscle mass and fat-free mass. However, there were no significant positional differences in several percentage-based measures, including percentage body fat and percentage muscle mass (Sebastiá-Rico et al., 2023a).
This suggests that even within a single sport, body-composition characteristics are not necessarily uniform.
It also challenges the idea that there should be a single body-composition target for every footballer.
Measurement adds another layer of complexity
A separate systematic review and meta-analysis involving 74 studies of professional male footballers found significant differences in reported fat mass, percentage body fat and fat-free mass depending on the assessment method and equation used (Sebastiá-Rico et al., 2023b).
This is not a trivial methodological issue.
If two methods produce different estimates, then comparing a player’s result against a published body-fat reference range requires knowledge of how the reference value was obtained.
A 12% body-fat result obtained using one method should not necessarily be treated as directly equivalent to 12% obtained using another.
Consequently, body-composition reference values should be interpreted in the context of the assessment method used (Sebastiá-Rico et al., 2023b).
Body-composition measurements have error
This issue extends beyond football.
Body composition can be assessed using skinfolds, bioelectrical impedance, DXA and other techniques. These methods have different assumptions and sources of measurement error (Pettersson et al., 2024; Moon et al., 2023).
A systematic review comparing DXA and bioelectrical impedance analysis in athletes found differences between the methods in estimates of body-composition compartments, demonstrating that they should not simply be regarded as interchangeable measurement techniques (Moon et al., 2023).
The practical consequence is that small changes should be interpreted cautiously.
The 2024 longitudinal athletics study provides a useful example. The researchers calculated the least significant change for their DXA measurements so that changes could be interpreted against the measurement precision of the equipment and protocol (Pettersson et al., 2024).
This is a considerably more robust approach than assuming that every change in a body-composition number represents a genuine physiological adaptation.
Does a lower body mass mean better performance?
Not necessarily.
A reduction in body mass can result from changes in fat mass, lean mass, water or combinations of these compartments.
Therefore, the direction of change in body mass alone does not tell us whether the intervention was beneficial.
This is particularly apparent when considering weight-category sports.
Research on combat-sport athletes demonstrates that rapid weight loss is common, but the effects of rapid weight reduction on performance are not uniform across studies and appear to depend on factors including the magnitude of weight loss, timing and the recovery period available before competition (Barley et al., 2022; Pereira et al., 2023).
A systematic review and meta-analysis found that rapid losses of up to approximately 5% body mass over less than seven days did not significantly impair some measures of physical performance in Olympic combat athletes (Barley et al., 2022).
However, this should not be interpreted as evidence that rapid weight loss is harmless or that it is an appropriate strategy for all athletes.
Other evidence has reported impairments in selected physiological and performance outcomes following rapid weight loss, with responses varying according to the protocol and outcome measured (Pereira et al., 2023).
The literature therefore supports a more nuanced conclusion:
weight loss does not have one predictable effect on performance.
What happens when athletes manipulate body composition gradually?
Gradual body-composition manipulation is different from rapid weight cutting.
A 2025 scoping review examined 73 international consensus statements, position stands and practice guidelines relating to body-mass and body-composition manipulation in athletes. Across the literature, recommendations generally emphasised individualised targets based on sport, position, sex, age and competition phase, rather than universal body-composition targets (Delany et al., 2025).
The review also found that relatively few of the guidance documents provided specific evidence-based targets for the magnitude, rate or timing of body-composition change, demonstrating that there remains substantial uncertainty in this area (Delany et al., 2025).
This is important because practitioners sometimes present specific body-composition targets with considerably more certainty than the underlying evidence justifies.
What about low energy availability?
This is an important consideration, but it should be kept in context.
Reducing body fat generally requires an energy deficit. If energy intake becomes insufficient relative to the demands of exercise and normal physiological function, low energy availability can occur.
The IOC consensus literature identifies low energy availability as an important health and performance consideration when athletes manipulate body mass or composition (Mountjoy et al., 2023).
However, this does not mean that all body-fat reduction is harmful.
A controlled, appropriately planned change in body composition is fundamentally different from chronic under-fuelling.
The 2025 scoping review of athlete body-composition recommendations found that current expert guidance generally emphasises gradual, individualised approaches that consider performance and health rather than simply maximising weight loss (Delany et al., 2025).
Therefore, the relevant question is not whether an athlete is losing body fat.
It is whether the process used to achieve that change is compatible with adequate nutrition, training and health.
The role of nutrition
Nutrition can influence body composition, but dietary changes do not necessarily produce predictable changes in athletic performance simply because they alter body mass.
A 2025 review examining dietary practices, body composition and sports performance highlighted the interaction between dietary intake, body composition and performance, while also noting that nutritional strategies need to be considered in the context of the athlete and sporting demands (Gough, 2025).
Similarly, a 2025 systematic review examining protein supplementation alongside endurance training found effects on some measures of body composition and physiological adaptation, illustrating that nutritional interventions can influence body-composition outcomes without necessarily producing uniform improvements across every performance measure (Sun et al., 2025).
This reinforces an important point:
body composition is an outcome influenced by nutrition and training, but changing body composition is not automatically synonymous with improving performance.
Body composition may change without fat loss
One of the more interesting findings from longitudinal athlete research is that changes in body composition do not necessarily follow the simple pattern of “less fat, more muscle”.
Pettersson et al. (2024) followed elite endurance and power athletes across a competitive season and found meaningful increases in lean mass in many athletes, while there was no significant overall change in whole-body fat mass.
Among male power athletes, body mass increased by approximately 1.4 kg, with a significant increase in lean mass of approximately 1.4 kg, while fat-mass variables did not significantly change (Pettersson et al., 2024).
This is useful because it demonstrates that an increase in body mass can occur alongside favourable changes in body composition.
In other words:
A heavier athlete is not necessarily a less athletic athlete.
The composition of the additional mass and its relationship with performance are what matter.
Body composition versus performance: which matters more?
This is arguably the most important question.
The critical review by Mathisen et al. (2023) found that body-composition measures were associated with performance in several studies, particularly endurance performance. However, training variables such as training volume and speed, and previous performance, were sometimes equally or more important predictors of future performance.
This finding is consistent with the broader sports-performance literature, where performance is influenced by multiple interacting physiological, technical and training variables (Sánchez-Oliver et al., 2025).
A recent study comparing endurance, strength and intermittent athletes also demonstrated that athlete profiles differ across multiple dimensions, including body composition, diet, physical activity and other characteristics (Sánchez-Oliver et al., 2025).
This makes it difficult — and probably inappropriate — to isolate body composition as a single determinant of performance.
Association does not equal causation
This is one of the biggest limitations of the current literature.
Suppose elite athletes in a particular sport tend to have lower body-fat levels than recreational athletes.
There are several possible explanations.
Lower body fat may contribute to their performance.
Alternatively, years of training may influence both their body composition and their performance.
It is also possible that genetics, training history, sport selection and other physiological characteristics influence both variables.
Cross-sectional research cannot fully distinguish between these explanations.
Longitudinal research provides stronger evidence, but even longitudinal observational studies cannot necessarily establish that a change in body composition caused the change in performance.
Intervention studies are therefore particularly valuable.
However, the evidence base remains relatively small.
The critical review by Mathisen et al. (2023) identified only 29 longitudinal, prospective or intervention studies specifically examining body composition and performance, with the majority involving endurance athletes.
That is a relatively limited evidence base considering how frequently body-composition targets are used in sport.
Is there an ideal body-fat percentage for athletes?
Based on the current evidence, there is no scientifically defensible universal answer.
Elite athletes demonstrate substantial variation in body composition across sports and positions (Sebastiá-Rico et al., 2023a; Pettersson et al., 2024).
The methods used to measure body composition can also produce different estimates (Sebastiá-Rico et al., 2023b; Moon et al., 2023).
And the available evidence does not identify a single body-composition threshold that consistently predicts superior performance (Mathisen et al., 2023).
Therefore, a body-fat percentage should not automatically be interpreted as:
good,
bad,
too high, or
optimal.
Its meaning depends on the individual athlete and the context in which it is being assessed.
What about young athletes?
This is an area where particular caution is required.
Body composition changes naturally during growth and maturation, and adolescent athletes are not simply smaller versions of adult athletes.
Consequently, adult body-composition targets should not be transferred directly to young athletes.
The IOC body-composition recommendations specifically advise against routine body-composition assessment in athletes under 18 years of age, except where there is a clear justification and appropriate professional oversight (Mathisen et al., 2023).
The rationale is not that body composition has no relevance to youth sport, but that the potential benefits of measurement need to be weighed against the risks associated with unnecessary focus on body weight and physique during a period of development (Mathisen et al., 2023).
So, should athletes try to change their body composition?
Sometimes.
The evidence provides a reasonable rationale for body-composition manipulation when there is a clear relationship between the athlete’s current composition and the demands of their sport.
For example, reducing excess fat mass may be useful where body mass has a meaningful effect on movement economy or performance.
Increasing lean mass may be useful where additional muscle contributes to force and power production.
But these are context-dependent decisions, not universal rules (Mathisen et al., 2023; Delany et al., 2025).
The 2025 review of international recommendations concluded that body-composition goals should be individualised according to the athlete, sport, position, sex, age and competition phase (Delany et al., 2025).
That is probably a more defensible approach than prescribing a particular body-fat percentage.
How should body composition be interpreted?
Body composition becomes much more useful when it is interpreted alongside actual performance.
For example:
Body composition changes + performance improves + health is maintained
→ potentially useful intervention.
Body composition changes + performance does not improve
→ benefit is uncertain.
Body composition changes + performance declines
→ the intervention may not have been worthwhile.
This is not a formal evidence-based decision rule, but it reflects an important principle in performance practice: the purpose of changing body composition should ultimately be linked to the athlete’s sporting outcome rather than the body-composition number itself (Mathisen et al., 2023; Delany et al., 2025).
What should practitioners monitor?
There is no single assessment that can answer whether an athlete’s body composition is appropriate.
Depending on the sport and athlete, useful information may include:
- Body mass
- Fat mass
- Fat-free mass
- Muscle mass
- Strength
- Power
- Sprint performance
- Jump performance
- Endurance performance
- Training load
- Training availability
- Recovery
- Nutritional intake
- Relevant health markers
The reason for using multiple measures is straightforward: body composition and performance represent different constructs.
A body-composition measurement can tell us something about the athlete’s physical makeup.
A sprint test tells us about sprint performance.
A strength test tells us about strength.
A match-performance measure tells us something about sporting performance.
None should automatically be used as a substitute for another.
A non-biased conclusion
So, where does the evidence leave us?
The claim that “leaner is always better” is not supported by the current literature.
There is evidence that higher fat mass is associated with poorer endurance performance in some populations, and there is evidence that lean mass is positively associated with performance characteristics in a number of sporting contexts (Mathisen et al., 2023; Pettersson et al., 2024).
However, these relationships are not universal.
Professional footballers demonstrate different body-composition characteristics between positions, but not all percentage-based measures differ between positions (Sebastiá-Rico et al., 2023a).
Competitive volleyball research has found that relative body fat does not appear to be a strong indicator of competitive level (González-Ravé et al., 2023).
Elite endurance and power athletes also demonstrate different body-composition profiles and seasonal adaptations, with changes in lean mass occurring without significant reductions in overall fat mass in a recent longitudinal study (Pettersson et al., 2024).
The evidence also demonstrates that measurement method matters, with different techniques producing different estimates of body-composition compartments (Moon et al., 2023; Sebastiá-Rico et al., 2023b).
Perhaps most importantly, the evidence base directly testing whether deliberate body-composition manipulation improves sporting performance remains relatively limited (Mathisen et al., 2023).
Therefore, the most defensible conclusion is:
Body composition can influence athletic performance, but there is no single body composition that defines an optimal athlete.
For some athletes, reducing fat mass may improve performance.
For others, increasing lean mass may be beneficial.
For others, maintaining body composition may be the most appropriate strategy.
And for some athletes, attempting to change body composition may offer little performance benefit while introducing unnecessary nutritional or health challenges (Delany et al., 2025; Mountjoy et al., 2023).
The question should therefore not simply be:
“How lean should an athlete be?”
or:
“What should this athlete weigh?”
A better question is:
“Is this athlete’s current body composition limiting performance, and is there good evidence that changing it will make them better?”
That question places body composition where it belongs:
as one component of performance, rather than the definition of performance itself.
Key takeaways
1. Body composition is associated with athletic performance, but the relationship is highly dependent on the sport, event and athlete (Mathisen et al., 2023; Pettersson et al., 2024).
2. Higher body-fat measures are associated with poorer endurance performance in some populations, but this does not establish a universal optimal body-fat percentage (Mathisen et al., 2023; Kettunen et al., 2025).
3. Lean mass is associated with performance characteristics such as strength and power, but increasing muscle mass is not automatically responsible for performance improvements (Makaruk et al., 2024; Wilson et al., 2025).
4. Professional footballers demonstrate positional differences in some body-composition measures, but not all measures differ between positions (Sebastiá-Rico et al., 2023a).
5. Different body-composition assessment methods can produce different results, meaning reference values should be interpreted alongside the method used (Moon et al., 2023; Sebastiá-Rico et al., 2023b).
6. Elite athletes can increase lean mass during a competitive season without necessarily reducing whole-body fat mass (Pettersson et al., 2024).
7. Evidence from weight-category sports suggests that the performance consequences of weight loss depend on the magnitude, method and timing of the intervention (Barley et al., 2022; Pereira et al., 2023).
8. Current international guidance supports individualised rather than universal body-composition targets (Delany et al., 2025).
9. Much of the body-composition/performance literature is observational, so association should not automatically be interpreted as causation (Mathisen et al., 2023).
10. The most useful body-composition target is therefore not necessarily the leanest or lightest physique, but the composition that supports the athlete’s specific performance demands while maintaining training capacity and health (Delany et al., 2025).
References
Barley, O.R., Chapman, D.W., Guppy, S.N. and Abbiss, C.R. (2022) ‘Rapid weight loss of up to five percent of the body mass in less than 7 days does not affect physical performance in official Olympic combat athletes with weight classes: a systematic review with meta-analysis’, Sports Medicine, 52, pp. 2527–2541.
Delany, L.V., Costello, N., Jones, B. and Backhouse, S.H. (2025) ‘Dietary recommendations for body mass and composition manipulation in male and female athletes: a scoping review of consensus statements, position stands and practice guidelines from international expert groups’, Sports Medicine, 55, pp. 2445–2487. doi:10.1007/s40279-025-02285-4.
González-Ravé, J.M., et al. (2023) ‘Body fat of competitive volleyball players: a systematic review with meta-analysis’, Sports Medicine – Open, 9.
Gough, L.A. (2025) ‘Dietary practices, body composition, and sports performance of athletes’, Nutrients, 17(19), 3102. doi:10.3390/nu17193102.
Kettunen, O., Mikkola, J. and Ihalainen, J.K. (2025) ‘Associations between body composition and performance in elite endurance athletes’, International Journal of Sports Physiology and Performance, 20(11), pp. 1530–1537. doi:10.1123/ijspp.2024-0506.
Makaruk, H., Starzak, M., Tarkowski, P., Sadowski, J. and Winchester, J. (2024) ‘The effects of resistance training on sport-specific performance of elite athletes: a systematic review with meta-analysis’, Journal of Human Kinetics, 91, pp. 135–155. doi:10.5114/jhk/185877.
Mathisen, T.F., Ackland, T., Burke, L.M. et al. (2023) ‘Best practice recommendations for body composition considerations in sport to reduce health and performance risks: a critical review, original survey and expert opinion by a subgroup of the IOC consensus on Relative Energy Deficiency in Sport (REDs)’, British Journal of Sports Medicine, 57(17), pp. 1148–1158. doi:10.1136/bjsports-2023-106812.
Moon, J.R., et al. (2023) ‘Agreement between dual-energy X-ray absorptiometry and bioelectrical impedance analysis for assessing body composition in athletes: a systematic review and meta-analysis’, Journal of Functional Morphology and Kinesiology, 8.
Mountjoy, M., Sundgot-Borgen, J., Burke, L. et al. (2023) ‘2023 International Olympic Committee’s consensus statement on Relative Energy Deficiency in Sport (REDs)’, British Journal of Sports Medicine, 57(17), pp. 1073–1097. doi:10.1136/bjsports-2023-106994.
Pereira, R., et al. (2023) ‘Effects of different rapid weight loss strategies and percentages on performance-related parameters in combat sports: an updated systematic review’, Sports, 11(3), 60. doi:10.3390/sports11030060.
Pettersson, S., Kalén, A., Gustafsson, M., Grau, S. and Caspers, A. (2024) ‘Off- to in-season body composition adaptations in elite male and female endurance and power event athletics competitors: an observational study’, BMC Sports Science, Medicine and Rehabilitation, 16, 90. doi:10.1186/s13102-024-00877-7.
Sánchez-Oliver, A.J., et al. (2025) ‘Multidimensional differences between athletes of endurance, strength, and intermittent sports: body composition, diet, resting metabolic rate, physical activity, sleep quality, and subjective well-being’, Nutrients, 17(7), 1172. doi:10.3390/nu17071172.
Sebastiá-Rico, J., Soriano, J.M., González-Gálvez, N. and Martínez-Sanz, J.M. (2023a) ‘Differences in body composition between playing positions in men’s professional soccer: a systematic review with meta-analysis’, Applied Sciences, 13(8), 4782. doi:10.3390/app13084782.
Sebastiá-Rico, J., Soriano, J.M., González-Gálvez, N. and Martínez-Sanz, J.M. (2023b) ‘Body composition of male professional soccer players using different measurement methods: a systematic review and meta-analysis’, Nutrients, 15(5), 1160. doi:10.3390/nu15051160.
Sun, W., et al. (2025) ‘Effects of protein supplementation on body composition, physiological adaptations, and performance during endurance training: a systematic review and meta-analysis’, Frontiers in Nutrition, 12.
Wilson, M.M., et al. (2025) ‘Association of body composition measures to muscle strength using DXA, D3Cr, and BIA in collegiate athletes’, Scientific Reports, 15.
What the evidence means in practice
The literature supports a performance-led rather than physique-led approach to body composition.
The strongest evidence does not suggest that athletes should be pushed towards a universal body-fat percentage. Instead, body composition should be interpreted in relation to the demands of the sport, the athlete’s individual characteristics, objective performance and longitudinal change (Mathisen et al., 2023; Delany et al., 2025).
The evidence is also stronger for some relationships than others. The association between lower fat mass and endurance performance is reasonably consistent in relevant populations, whereas evidence that deliberately reducing fat mass improves performance in an individual athlete is considerably less extensive (Mathisen et al., 2023; Kettunen et al., 2025).
Similarly, greater lean mass appears relevant to strength and power performance, but the performance benefits of resistance training cannot simply be attributed to muscle hypertrophy (Makaruk et al., 2024; Wilson et al., 2025).
Finally, measurement error should not be ignored. Different assessment techniques can generate different estimates, while longitudinal DXA research demonstrates the value of considering the least significant change before interpreting a small change as physiologically meaningful (Moon et al., 2023; Pettersson et al., 2024).
The evidence therefore supports a relatively simple principle:
Don’t optimise body composition for its own sake. Optimise it only when there is a clear, evidence-informed reason to believe that doing so will improve the athlete’s performance.










