Tailoring The Body for The Sport
Tailoring the Body
Understanding frame, muscle, and fat to match the athlete to the sport and the sport to the athlete.
In the previous post, we used physiological testing to map an athlete's strengths and weaknesses. The same principles apply to body composition. Athletes come in a wide variety of shapes and sizes, and each combination is better suited to some sports than others.
Some aspects of an athlete's shape can be modified: the amount of body fat, the amount of muscle. Other elements are largely fixed: the skeleton's bone lengths and breadths, the weight of internal organs. The key is to view the body as a combination of components that work together. Narrow-minded perspectives on body composition are, at best, performance-limiting and, at worst, a serious risk to the athlete's long-term health.
Setting a specific weight target for an athlete without considering their frame (shoulder width, hip width, wrist and ankle thickness) is reckless. A large-framed athlete should not aim for the same weight as a small-framed athlete. The consequences can range from being significantly underpowered to outright health crisis.
Athletes Come in All Shapes and Sizes
Consider the morphological differences between an elite heavyweight rower and an elite Kenyan marathoner. Based on actual anthropometric studies, the contrast is striking:
Frame: ~40kg · Thigh girth: 63cm
Frame: ~26kg · Very light-boned
The height difference is 13%, but the shoulder width difference is 23%. The marathoner is not just shorter; they are dramatically narrower and lighter-boned. These are fixed framework differences that cannot (and should not) be trained away. They represent the starting point around which everything else must be shaped.
Kate Slatter and Megan Still
In the late 1980s, the Australian Institute of Sport's Talent Identification Program tested school students for physical attributes suited to rowing, a sport most Australians never get to try. Among those identified were Kate Slatter and Megan Still. Three years after first stepping into a rowing shell, the pair won their first National title. Three years after that, they won Olympic Gold at the 1996 Atlanta Games. This is the power of matching physical attributes to the right sport.
What Makes Up an Athlete's Body?
Every athlete's body can be broken into four fundamental components, two of which are largely fixed and two of which are modifiable:
Bone mass is fixed and should stay that way. Drops in bone mineral density (visible on DEXA scans) are a serious warning sign, usually indicating insufficient caloric intake. Organ mass makes up the majority of trunk weight and doesn't contribute directly to movement. Fat mass is the most readily modifiable "dead weight," but must be kept within healthy limits. And muscle mass is the critical variable: it is the engine that moves the frame.
Muscle moves stuff. The eternal dilemma: while less fat is generally good, less muscle is very bad. Far too many athletes put too much weight on losing fat and not enough on building and preserving muscle.
DEXA Scanning
DEXA (Dual-Energy X-Ray Absorptiometry) is the current gold standard for body composition analysis. By passing two different low-dose X-ray beams through the body, it differentiates between fat, muscle, and bone with high accuracy and provides regional breakdowns (arms, legs, trunk).
From an athletic perspective, the most important outputs are:
Bone Mineral Density is expressed as a T-score (comparison to a healthy young adult). A T-score above -1.0 is normal; between -1.0 and -2.5 indicates osteopenia; below -2.5 indicates osteoporosis. I've seen young athletes with the bone density of 70-year-olds. Even before reaching clinically significant levels, trends in BMD serve as critical yellow flags. Any downward trend in an otherwise active athlete usually points to an energy deficit that needs addressing.
Total Fat Mass from DEXA includes both subcutaneous (under-the-skin) and visceral (deep, organ-surrounding) fat. For lean athletes, the DEXA number can be nearly double what skinfold testing shows because calipers only capture subcutaneous fat. This makes DEXA unpopular among lean athletes, but the number is more complete and more honest, especially regarding metabolic health implications.
Appendicular Muscle Mass is calculated from the lean mass of all four limbs (since limbs contain no organs, lean mass is effectively muscle). Using Kim et al.'s conversion formula, this can be scaled up to total skeletal muscle mass: SMM = 1.19 x Appendicular Mass - 1.01.
The muscle mass equation
With a cap on the aerobic trainability of muscle (approximately 185 ml O2/min per kg for men, 200 for women), a relatively fixed frame mass, and a target VO2max, finding the optimal muscle mass becomes an engineering problem:
Target SMM = 0.77 × Frame Mass + 0.38 × Fat Mass + 0.75 × VO₂ - 55
A key insight from this equation: losing fat does help, but not as much as many think. Dropping from 16% to 8% body fat only reduces the required muscle mass to hit a given VO2max by about 2 kg. The balance between building muscle and losing fat matters enormously, and sacrificing muscle in the name of weight loss is one of the most common and costly mistakes in endurance sport.
Anthropometric Measurements
DEXA scanning is the gold standard but is expensive (~$100-200 per scan), involves small amounts of radiation, and isn't practical at high frequency. For regular monitoring, anthropometric measurements (skinfolds, girths, and bone breadths taken with calipers and a tape measure) offer a cost-effective alternative that, when performed by a trained practitioner, provides similar levels of accuracy.
I recommend the same approach as with metabolic and lactate testing: cheaper skinfold assessments every few months, backed up by a full DEXA scan every couple of years.
From a standard set of 10 skinfold sites, limb girths, and bone breadths, you can estimate body fat (using Jackson and Pollock equations), skeletal muscle mass (using the Matiegka equation), and frame mass (total weight minus fat and muscle). These can be tracked against the benchmarks from the previous section and plugged into the muscle mass equation to assess whether the athlete has sufficient engine for their frame and fitness goals.
Somatotype: mapping your body type
Anthropometric data also enables calculation of an athlete's somatotype: a three-digit score representing endomorphy (fatness), mesomorphy (muscularity), and ectomorphy (linearity), each on a scale of roughly 1 to 7. Using the Heath-Carter formulas, these numbers can be plotted on a three-axis chart to see where the athlete fits relative to different sports.
The data reveals a clear pattern. Across almost all sports, mesomorphy (muscularity) is above average, and endomorphy (fatness) is below average. The differences between sports then come down to the balance between mesomorphy and ectomorphy: rowers and swimmers are more muscular, while marathoners and distance runners are more linear.
Beyond somatotype, anthropometric measurements reveal telling structural differences. Elite shot-putters have a mean shoulder width at 3 standard deviations above the population norm. Elite high jumpers are almost a full standard deviation below the norm. These small skeletal differences become decisive at the highest levels of sport.
We've gone head to toe in this post, examining the significant differences among athletes and sports. Some characteristics are modifiable (muscle mass, body fat), while others are not (bone lengths, frame size, organ weight). Athletes come in all shapes and sizes, but so do sports. No matter the shape of the athlete's frame, whether long and narrow and lithe, or short and wide and heavy, and everything in between, there is a sport that favors that particular combination.
The key is knowing your frame, understanding what can and can't be changed, and shaping the modifiable components around the fixed ones. In the next post, we'll bring together everything we've covered on testing (physiological, body composition, and training data) and move into the specifics of designing an individualized training plan.