Blood lactate concentration increases by 105–164% after both low-load and high-load resistance training in trained males, with no statistically significant difference between conditions, indicating that metabolic stress is similarly induced regardless of load when volume is equated.

When muscles perform many repetitions with moderate or light weights, they burn sugar quickly and produce a lot of lactate. This lactate builds up inside the muscle cells, making the inside more crowded with molecules. Water follows these molecules into the cells, causing them to swell. This swelling happens whether the weight is light or heavy, as long as the total number of repetitions and effort are the same.