Earlier during your workout, you might have thought you were starting to see some muscle definition. "Called transient hypertrophy, or a muscle pump, this physiological phenomenon occurs when blood rushes to your muscles to supply them with workout-powering fuel and even jump-start the recovery process," explains certified strength and conditioning specialist Samuel Simpson, co-owner and vice president of B-Fit Training Studio in Miami. He notes that this muscle pump often starts mid-workout and subsides within a few hours after leaving the gym. And as the muscle pump deflates, it's easy to lose determination.
When it comes to building muscle, your body only knows or cares about the tension, fatigue and damage an exercise is generating… not the type of equipment you were using when performing that exercise. It really couldn’t give the slightest crap about that. For this reason, ALL types of exercises and ALL types of equipment are capable of stimulating muscle growth.
It is known that intracellular energy depletion (assessed by a depletion of ATP) stimulates AMPK activity in order to normalize the AMP:ATP ratio, and when activated AMPK (active in states of low cellular energy and colocalizes with creatine kinase in muscle tissue) appears to inhibit creatine kinase via phosphorylation (preserving phosphocreatine stores but attenuating the rate that creatine buffers ATP). While phosphocreatine technically inhibits AMPK, this does not occur in the presence of creatine at a 2:1 ratio. It seems that if the ratio of phosphocreatine:creatine increases (indicative of excess cellular energy status) that AMPK activity is then attenuated, since when a cell is in a high energy status, there is less AMP to directly activate AMPK.