Accentuated Eccentric Loading: Training and Research
In this article
What is accentuated eccentric loading?
Today, there are more advancements in health and fitness than ever before. With constant updates on proper exercise choices, recovery methods, nutrition tactics, and more, people are bound to feel overwhelmed. Eccentric muscle actions can produce high force at a lower metabolic cost for a given force. Their effects on power, muscle growth and strength depend on the training protocol. Beyond that, it is the root of all exercise, muscle contraction.
When exercising, it may seem as though most elements are all one movement, without thinking about the returning motion as a part to focus on. However, the two muscle contractions are vastly different in terms of force generation, maximum force production, and energy cost, according to a 2017 study. During any standard lifting exercise, there is the eccentric or lengthening contraction and the concentric or shortening contraction.
The cited 2022 narrative review describes Accentuated Eccentric Loading (AEL) as a heavier load in the eccentric portion than in the concentric portion within a complete stretch-shortening cycle. Simply emphasizing or slowing a lowering phase does not necessarily make it AEL. Eccentric actions can generate greater force than concentric actions, which is one rationale for studying different eccentric and concentric loads. The difference depends on the exercise and testing conditions.
As a result, AEL has been incorporated into rehabilitation, athletic performance, and muscle hypertrophy.
How does eccentric force differ from training outcomes?
Eccentrics started to become noticed when A.V. Hill, a 1922 Nobel Prize recipient in Physiology and Medicine, and Wallace Fenn presented the “negative Fenn effect”. This is explained in a 2021 study that a given force produced through eccentric muscle action requires a lower metabolic cost than isometric and concentric muscle actions. This has led to eccentrics becoming a chosen form of strength training in athletic settings as well as in physical therapy/clinical settings.
AEL has been studied for specific performance outcomes; this does not by itself establish prevention of future injuries. Additionally, in 1976 Bigland-Ritchie and Woods conducted a study comparing energy cost when cycling at a given speed, which found that concentric contractions used six times the energy of eccentric contractions. Because of this, eccentrics began being implemented for active muscular recovery in clinical and elderly populations.
How do general eccentric and AEL rehabilitation examples differ?
Due to these properties, Accentuated Eccentric Loading has been adapted to therapeutic settings. AEL places a greater load on the eccentric phase than the concentric phase, but the eccentric load may be below, equal to or above concentric 1RM. The research loading examples are exercise-specific; 105%-120% is not a standard prescription for every patient. However, with that increased ability, untrained patients are unfortunately more likely to develop Delayed Onset Muscle Soreness (DOMS) when first beginning AEL training.
In this case, a phased approach may be implemented to prevent this. Familiarization and gradual progression appear in the research discussion. The cited review does not establish one acclimatization schedule for every patient or guarantee less muscle damage than traditional loading. Research on general eccentric exercise also includes clinical populations, which should be distinguished from supramaximal AEL. The cited 2021 review describes improved walking speed after combined concentric-eccentric strengthening in people with knee osteoarthritis.
The same review describes eccentric cycling in participants with coronary artery disease (CAD), with substantially more total work and similar hemodynamic responses compared with concentric cycling. This is a modality-specific finding, not proof of universal AEL rehabilitation or injury-prevention benefits. Lower metabolic cost for eccentric actions at a given force does not itself establish lower mechanical tissue strain or a margin of safety for every clinical population.
The rehabilitation examples warrant attention, but they do not establish AEL as a universally preferred modality.
What does the research say about muscle growth?
Another benefit of AEL is developing muscle hypertrophy. According to the Journal of Strength and Conditioning Research, maximal strength is 20-50% greater when performing an eccentric contraction as opposed to a concentric one. Studies have compared eccentric and concentric loading for muscle growth, with differing findings depending on the protocol and how work or load is matched. However, other research has suggested that eccentric actions create prominently region-specific hypertrophy.
According to a 2017 study, concentric training significantly boosted hypertrophy in the mid-portion of the vastus lateralis, while eccentric training affected the distal growth of the muscle. These regional differences do not establish a universally best combination. The cited review reports similar whole-muscle growth when work or load is matched, while regional adaptations may differ. There are some studies that took this investigation even further by taking muscle biopsies.
The cited 2017 review reports greater Type II muscle-fiber growth with eccentric loading in three of five comparisons. Findings differed between studies, and these general eccentric-training results do not establish a consensus that every AEL protocol produces greater hypertrophy or recruits motor units in the same way.
However, it begs the question of whether an added variable such as load size would affect hypertrophic benefits. Even though in a standard lifting paradigm hypertrophy is achieved with a lighter load (60-80% of 1RM), there is research from 2019 suggesting that heavier loads when paired with AEL can result in added hypertrophy. This can be referred to as supramaximal AEL. Weight-releaser studies use exercise-specific eccentric and concentric loads to examine power and other adaptations.
These research examples do not guarantee added hypertrophy or establish a single loading prescription; greater muscle damage is not itself proof of greater growth.
What acute performance findings are reported?
The wide range of AEL adaptations allows it to be a handy tool for multiple different training objectives. In addition to muscular hypertrophy, plyometric and explosive strength capacities have seen positive gains from AEL and other eccentric training. According to a 2001 study, whenever the muscle is lengthening, it acts as a compressible shock absorber. For example, when walking downhill, muscles lengthen under load and help brake movement, dissipating mechanical energy.
During running and jumping, muscle-tendon structures can also store and return elastic energy. Energy dissipation and elastic recovery are distinct mechanical roles. In 2021, testing of alpine skiers, as well as musculoskeletal injury rehab patients, showed that eccentric exercises containing decelerating external loads are ideal for an increase in explosive strength.
Additionally, testing in professional footballers using AEL in a jumping protocol resulted in a notable rise in peak power output. The cited 2021 randomized crossover study involved 23 male professional footballers and 20% or 40% body-mass loading conditions. Peak power improved acutely, while neither jump height nor peak velocity changed significantly. This does not establish long-term muscle growth or benefit in every population.
How do weight releasers and flywheels fit?
From these advancements, special equipment was developed for optimal AEL training. The weight releaser hook is a great way to add additional weight to complete supramaximal AEL repetitions for bench presses, or barbell squats. When they are set to the right height, they allow for added weight on the eccentric portion before releasing at the bottom of the movement, prior to the concentric portion. Following that, the concentric portion is completed with the remaining bar load.
When using heavier loads, the lifter will use slower pacing on the AEL portion, potentially decreasing overall performance. However, research from 2022 suggested that only using the AEL weight releasers on the first repetition, followed by up to 5 traditional reps within the set, will account for improved concentric performance. Additionally, the flywheel has been another piece of equipment shown to be beneficial for eccentrics.
However, since the peak force of the flywheel is dependent on the person, skill is a prominent variable for effectiveness. For less-experienced users, flywheel responses depend on skill and the exercise setup. That observation does not establish prevention of injury or a uniformly low-intensity session. On the contrary, more experienced athletes tend to have a much higher peak eccentric force when put under flywheel conditions.
Since that also results in them generating higher overall speed, this specific technique results in improvements regarding faster stimuli such as sprinting and jumping in athletic settings.
What does older-adult eccentric research establish?
A growing trend in eccentric exercise is its use among older populations to combat debilitating age-related muscle conditions such as sarcopenia. This is mainly attributed to aging adults finding it difficult to perform traditional resistance training movements. This often leads them to neglect training entirely. Lower perceived effort may make some eccentric exercise approaches feasible for older adults, but it does not establish greater adherence to AEL for everyone.
According to a 2021 study, eccentric loading works to older adults’ physiological advantages. With aging, the average adult will preserve over 20% more of their eccentric strength capacity than their concentric. Therefore, when targeted, the mean RPE will be substantially lower as eccentric exercise allows for lower energy cost and higher force production. This may be effective in the prevention of sarcopenia. Research has shown that there is a direct correlation between physical activity levels in older adults and the onset of sarcopenia.
Lower perceived effort does not by itself determine how often to train. The cited older-adult perspective notes limited evidence on frequency and progression. It has even been suggested in a 2023 study that the intensity of exercise-induced DOMS is reduced with age. The goal of older adults seeking exercise is to maintain their ability to perform daily tasks for as long as possible. The most viable option will be anything that allows them to train effectively and routinely with minimal discomfort.
Eccentric exercise programs have been studied for functional measures relevant to fall risk in older adults. The 2023 literature review summarizes older-adult training studies reporting changes in quadriceps muscle size, torque and functional measures such as walking, balance, stair climbing and chair-stand performance. These findings come from different studies, rather than a single 2023 trial. Changes in walking, balance and chair-stand performance are relevant to daily activities, but they do not by themselves establish prevention of falls or a guaranteed improvement in confidence or quality of life.
What questions remain for AEL research?
As more research comes out regarding the effectiveness of AEL and other eccentric protocols, there is predicted to be a major shift in the way people go about settling their strength training goals. Eccentric methods have been studied in rehabilitation, athletic performance and muscle hypertrophy. Eccentrics have been studied across therapeutic settings, sports teams, endurance and plyometric strength programs, and in older-adult research on function and sarcopenia.
Eccentric-specific equipment provides ways to study and apply different loading patterns. Lower metabolic cost should not be equated with less mechanical strain for every exercise or participant. As the world adopts these methods, eccentric exercise and Accentuated Eccentric Loading may pave the way for further scientific advancements in exercise physiology and rehabilitation.
References
Pull Quotes:
“AEL has been studied for specific performance outcomes; this does not by itself establish prevention of future injuries.”
“Lower perceived effort may make some eccentric exercise approaches feasible for older adults, but it does not establish greater adherence to AEL for everyone.”
“The wide range of AEL adaptations allows it to be a handy tool for multiple different training objectives.”