Eccentric Isometrics
The Ultimate Way to Strength Train
- Part 1 -
By Dr. Joel Seedman, PhD
Read Part II HERE
Key Points
Precisely executed movement patterns combined with eccentric isometrics offer numerous benefits for novice and advanced lifters alike.
Research based on muscle spindles, post-activation potentiation, and co-contraction suggests that eccentric isometrics can enhance power, torque, potentiation, stability, symmetrical loading, hypertrophy, and overall movement efficiency
Understanding how to use high levels of proprioceptive feedback elicited during eccentric isometrics allows the lifter to modify movement and fine-tune body positioning as a means of mastering technique, form, and overall muscle function.
Overview
Eccentric isometrics (EI’s) are by no means a new training technique. Many powerlifters, Olympic lifters, bodybuilders, and strength coaches have been advocating something similar for years. In fact if you make it a habit of combing the web for quality training information you’ve probably seen many an author promoting the idea of performing something similar to eccentric isometrics.
If it still doesn’t ring a bell the more common terms you may recognize include pause reps such as pause squats, iso-holds, yielding isometrics, eccentric quasi isometrics, extreme isometrics, iso-extremes and many other descriptions all depicting the same general principle. In essence these simply illustrate the idea of performing the eccentric or negative phase of a lift in a controlled manner and holding the stretched position for a given duration before completing the actual lifting phase/concentric phase portion of the movement.
Having employed nearly every training strategy imaginable with both my athletes and myself for over 13 years I can honestly say that I’ve found nothing more effective than EI’s for enhancing strength, performance, muscle mass, and muscle function. Before I get into the practical application of eccentric isometrics, I’m going to temporarily go “science-nerd” on you so get your thinking caps on. If you’re not into the science of resistance training you may want to skip this section and move onto “Practical Application”.
4 Reasons for Performing Eccentric Isometrics
Strength coaches will often give numerous reasons as to why pause reps are so beneficial such as “teaches you to stay tight out of the bottom/hole”, “cleans up technique issues”, “minimizes the contribution of the stretch reflex”, “gives confidence in the bottom position”, “eliminates excessive momentum”, and “minimizes the elasticity attributes of the muscle”. Although these are all valid, there are deeper scientific explanations as to why eccentric isometrics are so effective.
Reason #1: Increased Post Activation Potentiation
Several studies have found that overcoming isometrics (pushing or pulling against an immovable object) create an even greater post activation potentiation (PAP) response than standard heavy resistance (isotonic movements). Unfortunately there is little if any research regarding yielding isometrics/EI’s (lowering a load to a given position without allowing it to collapse further).
Being fascinated by EI’s as well as the lack of literature surrounding them I decided to examine this for my doctoral dissertation. In general the results of the study demonstrated a greater PAP response in both upper and lower body power than standard heavy resistance training (85-90% 1RM) as well as similar if not slightly greater potentiation compared to overcoming isometrics.
One of the explanations for this is related to fatigue and energy expenditure. All muscular contractions produce both fatigue and potentiation therefore minimizing the former and maximizing the latter is ideal for performance. According to research, concentric muscle actions (as well as isometrics performed when the muscle is trying to shorten) produce greater metabolic fatigue and require more energy expenditure than eccentric muscle actions due to greater ATP required for the excitation-contraction coupling process [1]
By minimizing the total time spent in the concentric phase as well as allowing greater time in between each concentric action this minimizes the amount of fatigue accumulated. Furthermore greater total time under tension (TUT) is placed on the muscle per repetition allowing greater motor unit recruitment via increased temporal summation. In essence this enhances potentiation all while producing less than normal fatigue and energy expenditure. Furthermore, because fatigue is the enemy of motor programming, minimizing the effects of fatigue allows the strongest and most efficient movement patterns to be etched into the CNS.
Reason #2: Increased Proprioception and Sensory Feedback
In our investigation we also examined the effects of eccentric isometrics on stability and symmetrical loading (percent of loading on left vs. right side). Results demonstrated two significant findings.
First, eccentric isometrics enhanced stability and symmetry in both upper and lower body compared to the control. Just as interesting was the fact that traditional training (standard concentric and eccentric phases using 80-90% 1RM) caused slight yet significant deterioration in levels of symmetry and stability. The latter results were most likely due to the fact that when allowed to perform standard lifting protocols, most lifters will inevitably reinforce pre-existing movement patterns, which often times are dysfunctional and flawed. However the improvements witnessed with the implementation of EI’s was most likely related to the exaggerated eccentric/stretched component of the movement.
Muscle spindles provide the greatest levels of feedback and proprioceptive information when they are stretched such as during eccentric isometrics. Ultimately movement modification, body positioning, neural firing patterns, and overall motor control are maximized from this heightened state of kinesthetic awareness and sensory-integrated-movement.
Reason #3: H-Reflex and Muscle Spindles
Research regarding the Hoffman (H)-reflex shows that heightened proprioception and torque production may be related. Because, H-Reflex is a reliable measure of the stretch reflex response and muscle spindle activation, the greater the degree of stretch (as long as the muscles don’t relax) the greater the H-reflex response. Interestingly an enhanced H-reflex response is one of the mechanisms researchers attribute post activation potentiation to [2]. Based on this concept, any training technique that isolates the eccentric position should theoretically enhance the H-reflex response, which should in turn optimize proprioception and potentiation simultaneously.
It should also be noted that although both overcoming and yielding eccentric isometrics produce similar levels of PAP, overcoming isometrics have little to no impact on proprioception. This is due to the lack of pre-stretch and pre-load immediately prior to the concentric contraction (both of which are typically witnessed in movements that involve eccentric motions) therefore feedback from intrafusal muscle fibers and muscle spindles is limited. Furthermore research has demonstrated that pre-stretch is not only a critical component for increasing force capabilities but it also offers protection against fatigue [3], a critical aspect of maximizing potentiation, proprioception and motor programing.
Although enhanced feedback from muscles spindles can largely be attributed to the exaggeration of the eccentric phase, there are several other related factors that help explain why eccentric isometrics are such a valuable tool for optimizing muscle function and performance.
Reason #4: Muscle Stiffness and Proprioception
One important component of muscle spindles and their ability to provide sensory information is muscle stiffness (a critical performance-related characteristic). Current research in this topic suggests muscle stiffness plays a critical role in the interplay of muscle spindles and Golgi tendon organs and their ability to work together for continual sensory integrated movement and proprioception [4]. Increased muscle stiffness appears to enhance muscle spindle output and information for improved movement feedback [5]. Improvements in force, torque, and power are also associated with increased muscle stiffness as such a state has been shown to heighten the stretch reflex response most probably due to mechanisms relating to intrafusal fibers previously discussed [4, 6].
In fact many of the so-called latest and greatest training tools such as Vibration platforms, balance boards, and unstable training devices were knowingly and in many cases “unknowingly” created with the primary purpose of enhancing muscle stiffness as a means of facilitating increased activity of proprioceptive mechanisms. Fortunately most if not all of these devices are unnecessary as properly performed EI’s provide the ultimate stimulus for enhancing muscle stiffness inevitably having the greatest impact on performance related characteristics.
There are several key factors that play a pivotal role in optimizing muscle stiffness all of which eccentric isometrics possess. First, in order to avoid collapsing and maintaining control during a prolonged eccentric phase, heighted muscle stiffness is almost subconsciously employed by the lifter out of pure necessity. Secondly, research suggests that eccentric accentuated training increases muscle stiffness through both mechanical and neuromuscular mechanisms thereby improving force absorption and enhancing injury prevention.
Fatigue or lack thereof also appears to be another key factor in controlling muscle stiffness. In essence higher levels of fatigue result in decreased levels of stiffness, which inevitably decreases proprioceptive function and torque. In contrast minimizing fatigue allows for optimal stiffness qualities thereby enhancing proprioception in the form of movement modification and fine-tuning of body positioning. As previously mentioned EI’s produce less fatigue than other training modalities due the exaggeration of the eccentric phase making them ideal for enhancing muscle stiffness.
Finally and perhaps the most important factor that affects muscle stiffness is agonist-antagonist co-contraction or co-activation. Studies suggest that increased muscle stiffness may in fact occur in large from ones ability to employ co-contraction at specific portions of movement [4, 7]. Furthermore co-contraction is pivotal for motor control and movement accuracy. [4]. More importantly research has demonstrated that the bottom of the eccentric position (where the eccentric isometric occurs) creates that greatest degree of co-contraction [8]. In turn this increases muscle stiffness, all of which as previously described improves torque, stabilization, proprioception, and movement efficiency.
It is worth noting from a neuromuscular perspective the idea predicated behind a high degree of agonist-antagonist co-activation in the stretched position can be likened to that of a sling shot effect. The greater the force pulled against the sling by another force such as an arm, the greater the tension of the sling and ultimately the more velocity the propelled object will have. The same is true of muscles.
Although a significant portion of eccentric movement can be attributed to gravity and load of an object there is also a degree of co-contraction that helps pull against the agonists to create an almost coiled or cocked position similar to that of the rubber band.
Furthermore, because increased co-contraction heightens activation of intrafusal fibers through enhanced levels of stiffness this produces an ideal scenario for maximal reciprocal inhibition on the subsequent concentric phase of the activity thereby maximizing power and force output (increased activity of agonists and relaxation of antagonists). Such a scenario is commonly witnessed in powerlifting bench press technique in which the back muscles are maximally contracted during the eccentric movement to create stability, tightness, and proper positioning as well as maximal power on the concentric phase.
Finally such heightened levels of reciprocal inhibition would theoretically mitigate autogenic inhibition from the Golgi tendon organs due to the fact that these mechanisms are polar opposites. Therefore they cannot occur simultaneously at high levels specifically because activation from intrafusal fibers would override the inhibition from Golgi tendons organs due to muscle spindles having faster conducting axons than Golgi tendon organs. In summary co-contraction may be a key factor for minimizing autogenic inhibition and maximizing reciprocal inhibition.
Because EI’s emphasize this stretched/eccentric position they represent the perfect training modality for capitalizing on all of these aforementioned neurophysiological principles.
Practical Application - 12 Key points
Now that we’ve covered the scientific rationale, lets get into the nuts and bolts of how to apply eccentric isometrics to your training regime.
Key point #1: The Movements
Focus on the basic human movement patterns. I typically break movements down into seven patterns. Three of these are lower body dominant and include variations of the squat, hinge, and lunge/stride. The other four are upper body movements and include variations of horizontal pull, horizontal push, vertical pull and vertical push.
Core stabilization is another category I often include when training clients particularly if the individual is lacking core strength. However, it should be noted that properly performed eccentric isometrics involve incredible core activation and stabilization therefore the need to incorporate excessive core work is often unnecessary. If you’re still desiring greater core activation don’t forget each movement pattern can be performed unilaterally such as single arm dumbbell press, or single leg RDL’s all of which greatly challenge the core musculature and rotational muscles particularly when performed as an EI. Therefore for the purpose of this article I’ll focus on the primary seven movement patterns listed above.
KEY POINT #2: Range of Motion
Each theory discussed in this article and how it pertains to EI’s is predicated on the fundamental principle of remaining tight and using the optimal/natural range of motion. In other words DON’T COLLAPSE! In fact there is research demonstrating a relationship between muscle stiffness, range of motion, proprioception, and fatigue.
In essence fatigue, faulty recruitment patterns, or conscientious relaxation of muscles leads to decreased muscle stiffness, thereby decreasing proprioception, and ultimately producing movements with larger range of motion (i.e. increased flexibility). Yes you read this correctly!!! Poor proprioception and large or exaggerated range of motion are related, one often leading to the other. Use a natural/full range of motion not an excessive ROM.
This is also related to the duration of the holds. If you pause for too long at the bottom position you will inevitably collapse. Remember the goal is proper motor programming which means programming the CNS in the way the body is meant to move not contorting the body into un unnatural position that overstretches the tendons, ligaments and connective tissue. In fact performing exaggerated positions using excessive range of motion is a surefire way of developing mobility, flexibility, and even spasticity issues. At this point the muscles are no longer absorbing force properly therefore inflammation around the joints and muscle accumulates inevitably leading to spasticity and dysfunctional movement patterns. So much for the notion of yoga being an ideal form of exercise.
The last thing you want is to train your body to breach its natural protective barrier that guards itself from being contorted into biomechanically and neuromuscularly compromised positions. In other words a natural full range of motion is desired but an excessive range of motion signifies the muscles had to relax/collapse indicating decreased stiffness, decreased sensory information from proprioceptors and most importantly the reinforcement of dysfunctional movement patters that will inevitably transfer to other related movements.
Furthermore this will compromise the potentiation response and most probably cause neuromuscular inhibition similar to how static stretching temporarily decreases power and force production (i.e. overly relaxed muscles). The aim is muscle spindle re-sensitization not muscle spindle de-sensitization.
For most movement patterns, optimal range of motion (approximately) will involve perpendicular positions, 90-degree angles, and parallel joint segments. Significantly deviating from these biomechanical constructs by incorporating extreme joint angles not only compromises torque and force production but also places undue stress on surrounding joints and connective tissue.
KEY POINT #3: Isometric Duration
Hold each eccentric isometric for 2-7 seconds. Less than this and you’ll forego the benefits associated with the lengthened position. More than this and fatigue accumulation can cause technique to deteriorate not to mention possible relaxation/collapsing during the stretched position. Furthermore the dynamic response of muscle spindles (research indicates this is more powerful than the static response) is thought to last for only several seconds therefore continuing much beyond this point is unnecessary and potentially counterproductive.
KEY POINT #4: Posture is Key
Proper execution of EI’s includes keeping a neutral spine. This involves a natural but not excessive arch. If you focus on achieving the largest stretch/depth during movement while simultaneously locking your spine into position, this will inevitably result in finding the appropriate range of motion. Therefore the proper posture for all EI’s, starting from head to toe involves keeping a tall and elongated head, shoulders pulled down, back, and in towards the spine, chest out, stomach pulled in, and hips back (don’t let the butt collapse into excessive posterior pelvic tilt, however avoiding excessive anterior pelvic tilt is just as critical).
Also keep the chest out without letting your core relax or your stomach/rib cage protrude outward. Finally be sure you avoid cervical hyperextension particularly on movements such as squats or hinges. This is quite common and often results from tilting the head up to gaze in the mirror, which ties into my next point.
KEY POINT #5: Lift by Feel not by Sight
Don’t use the mirror! Whenever you use the mirror, the image from the mirror reflects back to your retina and gets processed by your occipital lobe before the brain cognitively compares this image with the desired outcome of which further processing is required. Coordinating movement modification with the cerebellum combined with the previous steps can take 200-500 milliseconds which is roughly 8-10x longer than it takes proprioceptive mechanisms such as muscle spindles to respond (30-50ms). If you use the mirror to make corrections, by the time you’ve made the adjustments, the error has already transpired whereas muscle sensory receptors can detect these potential errors before significant movement deviations occur. In other words lift by feel not by sight.
The visual system can often act as a distraction keeping lifters from attending to other more important inherent sensory information. Don’t watch your way through the movement; instead feel your way through the movement. In fact, I often have my athletes close their eyes on many of their sets. You should essentially be able to handle 95% of the same load eyes closed that you can handle with your eyes opened for any lift (lunge pattern is the exception due to balance issues). If you’re unable to do this then your proprioceptors may need to be re-sensitized or your form may need to be adjusted. In any case eccentric isometrics are ideal for rectifying any of the above issues.
KEY POINT #6: Foot Activation
For all standing exercises (squats, RDL’s, Lunges, overhead press etc.), wear either the most minimalist shoes you can find (preferably zero drop) or go barefoot. Heightened levels of somatosensory feedback start with the feet, toes, and ankles. Normal shoes tend blunt this response. A good rule of thumb is the following: if you can't do the same weight (with perfect technique) barefoot, your mechanics are wrong. If that's the case, it's time to strengthen you feet and ankles to ensure proper alignment and body mechanics.
For more information on foot and ankle training click HERE.
KEY POINT #7: Breathing
Besides the fact the eccentric isometrics do wonders for correcting breathing patterns there are several components of the respiration process that need to be addressed during EI’s. During the actual movement, breathing will be kept to a minimum but it is still vital. Any deep breaths will be taken in between reps or at the initiation of the eccentric contraction. During the majority of the eccentric phase and EI you will either be holding your breath or lightly breathing as if sipping air through a straw. Essentially it will be a modified Valsalva maneuver.
If you take deep breaths during the eccentric phase you’ll lose tightness, collapse, and potentially injury yourself not to mention you’ll be performing the exercise using improper movement patterns. As previously mentioned muscle stiffness is critical for maximizing muscle function and proprioception. Deep breathing performed during an intense repetition will impair this. Whoever coined the idea of breathing in a controlled and relaxed fashion while lifting, obviously never lifted a heavy weight in their life.
KEY POINT #8: Rep Range
Although you can use any repetition range depending on your training goals, I generally recommend low repetitions in the 1-5 rep range. Aim for quality over quantity. With each repetition lasting 2-4 times longer than normal repetitions, time under tension for 3 reps will generally last as long as a traditional set of 8.
To paraphrase Christian Thibaudeau, we’re not chasing fatigue. Instead were aiming for deep activation and overload of all of the available muscle fibers and motor units in order to complete the task as efficiently and as powerfully as possible.
KEY POINT #9: Intensity and Load
Go as heavy as you can for the target reps while keeping textbook form and reinforcing the proper movement patterns. Start off with 50% or less of your 1RM. However, you should eventually reach the point where you are performing EI’s comfortably with 80-90% of your 1RM.
If you’re currently unable to do this, your form may be in need of some fine-tuning. Refer to my 12 Tests of Strength to determine where you currently stand in your overall strength and body mechanics. Above all, do not sacrifice weight for technique - take the opposite mindset.
KEY POINT #10: Take your Time
Don’t rush into subsequent repetitions. This is where you can catch your breath, regain your tightness, focus your mind on the task at hand, and be mentally engaged for the next rep. Tune into each facet of sensory-related information coming into your nervous system in order to make the repetition as perfect, strict, tight, and as powerful as possible. If you feel yourself getting loose, favoring one side more than the other, wiggling, or compensating with other muscle groups then make the necessary adjustments.
KEY POINT #11: Less Gravity, More Squeezing
During the eccentric isometric, try to feel tension building up within the muscles. Imagine your stretched muscles acting like a coiled spring or sling shot with your antagonist muscles firing fiercely to pull the weight into proper position as opposed to letting gravity do all of the work. With this in mind complete the concentric phase of the lift as powerfully as possible (release the spring/sling shot) while maintaining tightness and control of the load. Remember co-contraction of reciprocal muscle groups is paramount during the eccentric isometric for maximizing proprioception, power output (for the subsequent concentric phase), stability, and motor control.
KEY POINT #12: Looks Aren’t Everything
Just because it visually looks good means nothing. Intramuscular and intermuscular coordination as well as overall motor unit recruitment are something only the lifter themselves can inherently tune into. In other words, your muscles can sense more than what any coach can see. The better you get at adhering to all of this subtle feedback and sensory information from your muscles, the quicker you’ll master movement. Remember with eccentric isometrics you’ll have an abundance of proprioceptive information to adhere to as the majority of the movement will be spent under stretch and tension.
See Part 2 HERE
References
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de Haan, A., M.A. Lodder, and A.J. Sargeant, Influence of an active pre-stretch on fatigue of skeletal muscle. Eur J Appl Physiol Occup Physiol, 1991. 62(4): p. 268-73.
Kistemaker, D., et al., Control of position and movement is simplified by combined muscle spindle and Golgi tendon organ feedback. Journal of Neurophysiology, 2012. 109: 1126–1139, 2013.
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Brown, S.H. and S.M. McGill, How the inherent stiffness of the in vivo human trunk varies with changing magnitudes of muscular activation. Clin Biomech (Bristol, Avon), 2008. 23(1): p. 15-22.
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