By Cierra Bloom, ATC, LAT, MS, CES
The skeletal muscles in our bodies are the voluntary, contractile muscles that allow us to perform movements that are vital in everyday life. There are three different types of contractions that skeletal muscles can achieve through any movement: concentric, eccentric, or isometric. Concentric contractions involve a shortening of the muscle fibers to overcome the force being placed on them. Eccentric contractions are when the muscles are lengthened while contracting because the force is greater than the effort resisting them. Isometric contractions happen when the force and effort are equal, and the length of the muscle doesn’t change while contracting.
Multiple research studies have looked at the differences between movements where clients who eccentrically trained, concentrically trained, and a traditional eccentric-concentric training. Typical outcomes are an increase in muscular strength, endurance, hypertrophy, and retention of gains after detraining in anyone who weight trains. However, eccentric training tends to lead to retained maximum strength after detraining, and improves and maintains maximum repetitions.
Also, strength gains and hypertrophy are two very important aspects of any post-surgical rehabilitation. Specifically, following an ACL reconstruction, building strength of the quadriceps is extremely important. Multiple studies have supported the use of eccentric exercises to improve quad strength over traditional concentric exercises, and that is safe to do so. Eccentric training allowed for greater quadriceps strength gains immediately after surgery to up to one-year post-operation compared to concentric training.
It is believed that eccentric exercises have greater strength gains and retention than other exercises due to greater neural adaptations and control, or proprioception. Eccentric exercises involve a larger cortical area in the brain than concentric exercises, and they cause greater torque on the muscles and joints than concentric exercises, which allows for more neural control, which creates better neuromuscular connections and avoids more muscle damage. There also seems to be extra-cellular collagen upregulation days after repeated eccentric exercises, and this delayed stimulus allows for strength retention.
Eccentric training has greater effect on strength and hypertrophy gains than concentric resistance training in skeletal muscle. This is why eccentric resistance training is important for any training program, especially post-injury and post-surgery. In general terms, eccentric resistance allows the muscles being worked to withstand a greater force than an alternative concentric resistance with the same muscle group, because an eccentric load doesn’t require the muscles to initiate the movement, just resist it. If eccentric contractions can withstand a greater force/heavier weight, it is obvious that will allow the muscles to become stronger and in turn, hypertrophy, more so than a lighter concentric movement.