The Role of Eccentric Exercise in Early Season Training
By Kurt Jepson
Key goals for athletes involved in a dryland training program include strength enhancement and injury prevention. Eccentric exercise provides a pathway to achieving these goals simultaneously and should be a component of any thoughtful training plan.
Eccentric contractions, or “negatives” as often referred to in the fitness industry, are best defined as, “…. a muscle contraction which occurs when a force applied to the muscle exceeds the momentary force produced by the muscle itself, resulting in the forced lengthening of the muscle-tendon system while contracting (Lindstedt et al 2001)”. Functionally, this is ideally a “controlled” lengthening. These efforts are in contrast to Concentric contractions where the muscle is shortening against a load, or Isometric contractions in which there is no relative movement or positional change of the muscle or it`s associated limb structure.
Extensive research over the years has provided valuable information regarding the physiologic characteristics of eccentric muscle activity. Muscle morphology and neural adaption studies are typical areas of focus, as alterations in muscular function are seemingly related to these parameters.
All skeletal muscle contractions result in energy production and/or absorption. In the case of eccentrics, extrinsic load energy is absorbed by the controlled lengthening of the muscle and usually dissipated as heat. Some energy however is stored as potential or elastic energy within the muscle and tendon tissue for release later. This concept forms the basis of the “stretch shortening contractile cycle” (Standish et al 1986) as potential energy is recovered as kinetic energy. The “stretch” relates to the controlled elongation of the muscle under load and the “shortening” refers to the rapid contraction of the fibers immediately thereafter. Plyometric exercises are designed to take advantage of this principle. Time is a factor in this process. If energy is absorbed by the muscle lengthening over a “long” time, heat is the major byproduct. If energy is absorbed quickly, more is converted to potential/stored energy. Eccentric contractions thus provide a “shock absorbing” load dispersion function to the associated limb as well as “rebound” movement capabilities (LaStayo 2003). Functionally we split the work of locomotion equally between concentric and eccentric muscle activity (Heglund et al Am J Physiol 1987, Montgomery et al Am J Sports Med 1994). Given this, eccentric conditioning is vital to performance enhancement.
Eccentric muscle activity involves unique features not shared with concentric or isometric contractions. Greater forces are created via eccentric contraction efforts for a given angular joint velocity. They require less motor unit activation and have up to a four fold lower metabolic cost! Post exercise cardiorespiratory and targeted peripheral blood flow response are correspondingly reduced (Hotobagyi, Katch 1990, Abbott et al 1952, Overend et al 2000, Meyer et al 2003). Although not fully understood, variances are driven primarily at the neural adaptive level, both Cortically and at the motor end plate of the muscle itself. There appears to be an enhancement of Motor Cortex activity yet lower discharge of distal nervous structures (Hoppeler and Herzog 2014).
Anytime an athlete can “hyper- stimulate” stimulate the Central Nervous System (CNS), in this case the Motor Cortex, there is enhancement of movement pattern efficiency. This is vital to learning a new athletic skill or a return to proficiency post injury/immobilization. For older athletes subject to neuromuscular decline, it helps delay the aging process.
At the structural level the lower peripheral nerve activity and thus reduction of fiber recruitment in the associated muscle during forceful eccentric efforts, leads to microfiber overload and lesions (Friden and Lieber 1998, Crameri et al 2007, Lauritzen et al 2009). This “damage” in turn signals the body to adapt the stress tolerance of those fibrils. Muscle stiffness and spring characteristics are enhanced over time as fragile fibers are “culled”, leaving more tolerant fibers to survive and adapt. Stress also induces changes in the cellular matrix leading to “upregulation” of muscle cell activity and anabolic pathways (Douglas et al 2017). Adaptive repair improves the ability of the tissue to withstand future load and perform a given task with enhanced metabolic efficiency.
Histologically, fiber abnormalities are observed immediately post eccentric exercise bout but seem to peak 2-3 days thereafter (Morgan and Allen 1999), hence the term “Delayed Muscle Soreness/ DMS “. Type II or “Fast Twitch” fibers seem to be affected to a greater extent via animal and human studies. This dictates mindful dosage of eccentric exercise within the training week. Some muscle groups may require more recovery post stimulus. For example, static postural muscles (ie core) require less time between eccentric bouts than do acceleration groups (ie hamstrings).
These physiologic processes likely translate into injury prevention and enhance training. Interestingly, beneficial protective changes have been identified after a single eccentric exercise bout (Noska and Clarkson 1995) but as would be expected, seem to be more complete after several sessions. This “Repeated Bout Effect (RBE)” persists for several weeks to 6 months, following eccentric exposure, indicating long term adaptions which gradually dissipate over time (Crosier et al 1999, Hody et al 2011, Noska et al 2005).
Eccentrics have been shown to be an efficient way to rapidly improve strength by numerous investigators (Julian et al 2018). It appears gains are related more to cellular and neural adaptations, as muscle hypertrophy in most comparative studies is on par with a concentric exercise response. Eccentric load tolerance to failure can be 2-3 times that of isometric or concentric contractile abilities. The resultant added stimulation for adaption and strength gain is substantial. Perceived exertion is typically less than that experienced with similar load concentric work.
For example, LaStayo et al in 2000, looked at the effects of an 8-week program of ramped eccentric load up to 500 “negative” watts on subject’s ability to improve on a vertical jump test. Post testing revealed 12% gains beyond a control group that had performed similar concentric work (Am J Physiol Regul Integr Comp Physiol). In a 1993 animal biopsy study, Kubo demonstrated a 30% gain in “energy modulus” (Young`s Modulus) after just 8 weeks of eccentric training. This energy modulus can be transferred to contractile power by the working muscle. Recall that speed of load application in eccentric mode enhances potential energy within the contractile unit. With logical progression, eccentric to plyometric exercises can be extremely useful as they employ these physiologic principles. The key is a “logical” progression given the high training forces involved. Tendons in particular are hypovascularized, prone to injury and slow adapting during a healing process. Too much, too soon will frequently lead to tendon and/or joint irritation.
What does a program look like involving eccentrics?
Given the high loads to be utilized down the road, I recommend a period of sustained isometric exercise preparing the muscle groups which will be targeted by eccentrics. Having a sound loading strategy is the best way to avoid undesirable side effects of eccentric exercise on the musculotendinous unit which could potentially interrupt training. Isometrics have been used for years in rehab settings to stimulate the return of normal mechanical properties within degraded tendinous tissue post injury or immobilization (Reeves et al, Strength Training Alters the Viscoelastic Properties of Tendons in Elderly Humans. Mus Nerve 2003).
Isometrics can be utilized numerous times a week as tendon tissue has a low metabolic rate and require limited recovery time (Langberg et al 1999, Lavagnivo et al 2003). DMS will drive frequency from a muscle tissue recover standpoint. Sustained contractions over 20 seconds per rep have been reported to enhance stiffness and cellular adaptations (Kubo et al, Effects of Different Duration Isometric Contractions on Tendon Elasticity in Human Quadriceps Muscles. J Physiol. 2001). I would recommend 20-60+ second reps x 4 x 1 set each region. Load should approximate 25% of maximum volitional contraction (MVC) to start but can be transitioned to 75%+ over a couple of weeks provided no symptoms result. The limb should be positioned in the midrange of motion for the effort. This negates adverse tendon compression at the origin or insertion and takes advantage of the muscle`s ideal contractile length-tension characteristics.
Examples, midrange isometric holds;
Lower quadrant- “wall sits”
Upper Quadrant- “combined scap protraction retraction holds”
Core hip combined- “glut lateral core holds”
Gym equipment may be utilized and is useful in joint positioning and dosing/tracking load progression.
This preparatory phase should last 2 weeks to 2 months based on several factors including, but not limited to; athlete age, experience with rigorous training regiments, history of injury specific to that body part, etc. As depicted above, exercises can replicate familiar positions with the 20-60 second “hold” effort replacing the traditional rep and set mode.
The eccentric phase of training can begin after tolerant completion of the prep phase. If athletes are accustomed to high load exercise, are post adolescence, and are not recovering from injury, they can gradually mix eccentric exercises into their isometric phase.
Eccentric exercise should be a precursor to plyometric activities. Again a 2+ week timetable should be employed before rigorous “plyos” are included in the training routine. Frequency can follow the athlete’s usual schedule for resistance training. Sets of 6 -10 repetitions are typical. Recall that as speeds of eccentric contraction increase so do individualized fibril loads. Early eccentrics/negatives should therefore be done with a slow tempo (ie 5-6 count down/lowering) in order to determine musculotendinous tolerance via unreasonable DMS or other inflammatory signs. If “slow” negatives are tolerated, the speed of lowering the load can increase.
To design exercises the athlete must only think of what resistive movements can be completed in the “up with two, down slow one” mode. A classic example is using body weight resistance on the edge of a stair for calf eccentrics.
The up phase utilizes both calves and the controlled lowering eccentric phase (right leg) is completed with balance assist only from the left side (below). Hand weights may be utilized as tolerated.
Resistance bands may also be used to apply load once the appendage is placed in the initial work position, then tensioned and the induced load is controlled “negatively” through the range of motion. Any leg group, or for that matter any body part, can be exercised accordingly.
Example below; athlete walks back to tension band then performs eccentric contraction.
Example below; ankle placed in position, band tensioned and eccentric contraction performed.
Athletes may logically progress to high loads over time. In an Achilles complex study, Arampatzis et al reported that working at 90% of MVC caused only 5% tendon strain and that 90% load was required to yield increased stiffness and cross-sectional area compared with working at 55% MVC (L Exp Biol 2007). Recall that 90% of MVC eccentrically will “feel” lighter than if one completed the same resisted movement concentrically.
Eccentric exercise is only limited by available load source and one`s imagination. “Up with two down slow one” squats, pull-ups, push-ups, supine bridges, chair lunges, box step ups,…… the list is endless. Free weights or bands allow increased loads. Foam pads and wobble devices add a proprioceptive challenge. Training partners can add further options.
Spot max assist to raise bar, athlete eccentrically lowers (below).
When plyometric work is initiated special attention should be focused movement specificity, logical progression of load and repetition, competence, exercise tolerance and utilization of the stretch shortening cycle to its maximum potential. Recall that the speed of lengthening correlates to the degree of load and how much energy can be converted during the “explosive” shortening phase. Faster speeds produce higher loads, quicker rebound and stress induced adaptive processes over time. Again, progression is the key to plyometric tolerance.
For example, “playground” skipping can be advanced to “power” skips when the athlete demonstrates proficiency. Uphill broad jumps can be transitioned to one leg bounding when movement quality justifies it and the athlete is without symptoms. Box jumps can be completed with exercise bands to cue proper hip activity. Height is incremental to athletic stage and time on the ground should be minimal prior to the rebound (hot feet cue).
Youth coaches should pay special attention when introducing plyometric activities to younger athletes, as their Physeal (growth plates) structures are immature and prone to overuse injury. Dose accordingly.
This site is an excellent resource of exercise videos which focus on plyometric progression and specificity to Nordic skiing. They should be viewed/ reviewed by athletes, coaches and program developers prior to participation in this mode of training.
Video: NTS intro to Plyos