When it comes to exercise programs, especially weight based programs, there is always lots of debate as to what is the best method to gain strength and muscle mass. Lots of times we hear from athletes "I want to be bigger", being bigger isn't always the answer. What are the demands of your sport? What is your goal? Many times it comes down to wanting to be faster and have more power. Yes, increasing muscle mass plays a roll in both of these, how you train will play an even bigger role. It's not always who lifts the biggest weights that will perform the best.
There are three main types of muscle contraction, concentric, eccentric and isometric. Concentric is the type most people think of example a bicep curl. By contracting the bicep muscle the elbow flexes and the forearm moves towards the shoulder. Eccentric is the muscle contraction that occurs when the muscle is lengthening. Example, what happens after you do the bicep curl and your arm returns to the start position. Isometric contraction is when the muscle contracts but no movement occurs, think standing in doorway with arms pressed to the frame.
We will focus on the eccentric movement and its role in both injury prevention and performance (hint they are the same thing, without injury prevention performance can not be optimal).
The lengthening of the muscle in an eccentric contraction stimulates the the stretch-shortening cycle, creating a spring like mechanism, therefore more potential energy is stored in the muscle prior to the concentric (shortening) action. More potential energy = greater force. We also get greater force output do to the increase in muscle activation, it has been found that more muscle fibers are recruited during eccentric contractions thanks to improved neuromuscular adaptation. (Trust us this is a good thing)
The advantages of using eccentric exercises in your training and rehab program are
increased mass, strength and power of the muscle (performance & injury prevention)
increased power (performance)
the activation of the full muscle tendon unit (performance & injury prevention)
increased ability of the muscle and the musculotendon junction to absorb energy (injury prevention)
the tissue failure threshold increases (performance & injury prevention)
bone mass increases due to the increased force of the muscle (injury prevention)
By incorporating at least one exercise to each muscle group that involves eccentric contraction, you are positioning yourself to decrease injury and increase performance. Which is really the long and short of sport.
References used
Exercise Physiology - Energy, Nutrition and Human Performance (Fifth Edition)
Essentials of Strength Training and Conditioning (Second Edition)
Eccentric Muscle Contractions: Their Contribution to Injury, Prevention, Rehabilitation, and Sport (Journal of Orthopedic and Sports Physical Therapy, 2003)