What effect does bar speed, or time under tension, have on hypertrophy?
Short Answer: taking 4 seconds to lower the bar might aid hypertrophy for experienced lifters. If you’re a new trainee, bar speed doesn’t matter.
There’s more than one way to achieve hypertrophy. When talking about bar speed, we’re using mechanical tension and metabolic stress. Here’s how bar speed uses those two tools of hypertrophy:
Lifting heavier weight uses more motor units. We use more muscle fibers when lifting a heavier weight. But using light weight for a prolonged period of time, such as in slow sets, can result in hypertrophy too.
Slower bar speed is better for metabolic stress than fast bar speed. Metabolic stress comes from the buildup of metabolites like blood lactate, intramuscular lactate, glucose and glucose-6-phosphate within the muscle. AKA, things that make your muscles burn like shit. Slower reps cause much more metabolic stress.
Protein Synthesis: limited evidence, but promising so far.
On Trained Individuals: a 4-second eccentric works for experienced lifters.
If you’re a new trainee (1 year or less) it doesnt matter. For more experienced lifters, follow the principles of mechanical loading and metabolic stress. Train heavy for mechanical loading and light with slow eccentrics for metabolic stress.