Why do I look bigger after training?
It is a pump, plus swelling: blood and fluid move into the muscle during a session, and some damage-related swelling follows for a day or two.
Three things stack up. During the set, blood fills the muscle and fluid shifts into it, which is the pump and fades within an hour or two. For a day or two after an unfamiliar session, swelling from muscle damage adds to it. And across the week, how full your muscles look tracks how much carbohydrate you have eaten, because glycogen brings water with it.
All of it is temporary, which is why you can look sharp after a session and flat on a rest day with low carbohydrate. The real measure is the same as always: the weight on the bar going up over months, and a photo taken in the same light.
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- Damas, F. et al. (2016). Resistance training-induced changes in integrated myofibrillar protein synthesis are related to hypertrophy only after attenuation of muscle damage. J Physiol 594(18). Measurements in the first weeks of training are inflated by swelling from muscle damage, not by new muscle.
- Kreitzman, S.N. et al. (1992). Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. Am J Clin Nutr 56(1 Suppl). The other half of the effect: glycogen is stored with three to four parts water, so a well fed muscle is a fuller muscle.