Why are we stronger eccentrically?
When talking about strong muscles, our instinct is to think of the muscle force produced as it shortens, also known as a forceful concentric muscle contraction usually producing a movement as an outcome. Other contractions include isometric (muscle produces force without changing length), isokinetic (muscle contracts at a constant speed) and eccentric, where the muscle lengthens under tension as it controls or absorbs force. While the force output during a push or pull action might feel harder, research suggests that an eccentric contraction (the action of lowering a weight) produces greater output. It seems counterintuitive, so why are we stronger eccentrically?
Eccentric movements produce a larger output due to the way the body recruits muscles during lengthening. This is governed by mechanical, neuromuscular and structural advantages. During eccentric movements or muscle lengthening under tension, greater force is produced with less energy requirements and passive elastic components contribute to this. Furthermore, the central nervous system imposes less inhibitory control, enabling higher force output before protective reflexes activate. Although fewer motor units are recruited, they are typically high-threshold, stronger units that fire at higher rates, resulting in a greater force-per-unit ratio. Lastly, structural adaptations occur over time due to the repetitive eccentric loading such as increases in length and enhanced tendon stiffness which provide a protective mechanism against injuries.
Football is a dynamic, multi-joint movements sport and involves a high volume of eccentric actions, such as decelerating, cutting, change of direction or absorbing impacts from landings or tackles. These actions usually happen at high speeds and demand great eccentric control, especially by the large muscle groups hamstrings, quadriceps, glutes as well as calves muscles.
While all forms of contraction are key for optimal athletic performance, it is during eccentric movements that most injuries occur thus their adequate training is key for injury prevention. Eccentric strength in the hamstrings and quadriceps stabilizes the knee joint lowering ACL risk as well as decreases risk of hamstring strains during sprinting. Frequent training focused on developing eccentric strength is also beneficial for performance enhancement as it leads to muscle hypertrophy (fast-twitch fibres) and an improved rate of force absorption (faster stop/acceleration phase) which is translated to an overall enhanced explosiveness and agility response.
Eccentric strength development can be effectively targeted through specific exercises which, with the adequate planning in frequency within the microcycle and mesocycle periodization models, are key to a successful training and prevention program. These are: nordic hamstring curls (strengthen the hamstrings eccentrically to reduce the risk of sprint-related strains, especially during high-speed deceleration), slow eccentric back squats (improve control and force absorption in the quads and glutes, enhancing braking ability and joint stability), drop landings and depth jumps (absorb impact forces safely through the lower limb musculature, reducing injury risk during jumping and cutting; use the stretch-shortening cycle to improve reactive strength and control during rapid deceleration and reacceleration), Romanian deadlifts (target the posterior chain eccentrically, especially hamstrings and glutes, for enhanced hip stability and sprint performance) or reverse nordic curls (focus on eccentric strength of the quadriceps, aiding in knee joint protection during explosive movement and landing).