What is the primary limitation of using skinfold calipers for precise long-term tracking of body fat changes in an individual undergoing a bulking phase?

The primary limitation of using skinfold calipers for precise long-term tracking of body fat changes in an individual undergoing a bulking phase stems from the fact that skinfold calipers primarily measure subcutaneous fat, which is the fat located directly beneath the skin. A bulking phase involves a deliberate caloric surplus and resistance training to maximize muscle mass gain, often accompanied by some fat gain, leading to dynamic and complex body composition changes. During this phase, the distribution of subcutaneous fat across the body can change non-uniformly, meaning fat gain may be more pronounced in some areas than others. Furthermore, significant muscle hypertrophy, which is the increase in muscle cell size, occurring beneath the measurement sites can alter the skinfold thickness by pushing the subcutaneous fat outward or changing tissue density, making it challenging to differentiate actual fat accumulation from structural changes in underlying muscle. This non-uniform fat distribution and the influence of underlying muscle growth mean that the sum of skinfold measurements, or the body fat percentage derived from them using predictive equations, may not accurately or consistently reflect the precise, proportional changes in total body fat over time in an individual whose body composition is rapidly and unevenly shifting.