There are two main types of muscle contraction that bodybuilders are interested in. An eccentric (or negative) muscle contraction is when the muscle lengthens under tension, generally by lowering a weight. A concentric muscle contraction occurs when a muscle shortens under tension, usually by raising a weight.
Some studies show that the eccentric component of an exercise is essential in promoting muscle hypertrophy (growth) because more muscle damage occurs during this phase. This damage leads to the development of thicker muscle fibers to resist further damage induced by exercise. However, regarding the hormone response to these contractions, a team of scientists from Southeastern Louisiana University have answered your question specifically.
The researchers assessed 10-men who exercised with weights using either eccentric or concentric muscle contractions. The subjects performed only the eccentric or concentric portion of the lift using the same amount of weight. The researchers took blood samples from these men before the exercise and at regular intervals during and after the workout. These blood samples were assessed to determine concentrations of anabolic hormones.
Results showed that both types of contraction increased free and total testosterone levels equally. However, concentric muscle contractions increased both lactate and growth hormone levels significantly more than eccentric contractions. This is because it takes more energy (in the form of ATP) to lift weight than to lower weight.
Some lifters experiment with only the negative portion of a lift during training. However, both contractions seem vital to triggering the optimal anabolic response from training. I’m a big believer in the frequent use of straight sets and reps using maximum overload in the Max-OT program. Based on the research, this training approach also seems to provide the greatest anabolic hormone response.