Personally, I think it makes a shit ton of sense and has prudence for athletic populations and those in rehab-based training. This is another one of those ‘nuanced’ techniques that most sport scientists or researchers will tell you is pointless and “not statistically sound”, whereas some strength coaches will vehemently suggest otherwise. Not to mention, they are about as mechanically disadvantageous as could be for exercises like full-range back squats. You’ll see this most often with basketball players, as the majority of their sport is played at low angles of knee flexion. Joint angle specific training is another aspect of isometric training that has been subject of debate in recent years, creating quite a bit of fervor among strength coaches and sports scientists. Simply stated an athlete with the ability to recruit and fire more muscle fibers is a stronger, more explosive athlete, and similarly, an athlete who can recruit these fibers faster is likely to improve their success in competition. Increasing motor unit recruitment and rate coding are wildly important for athletic populations, and some would argue are the differentiating traits between ‘good’ and ‘great’ athletes. Rate coding refers to increasing the rate at which these fibers fire… I know, go figure. Motor unit recruitment refers to the precise number of muscle fibers that fire (or contribute) during muscular contraction (4). That said, my belief (also reasonably supported by research) is that isometric training is a highly effective way of increasing neuromuscular traits such as motor unit recruitment and rate coding (4). The purpose of isometric emphasis isn’t quite as cut and dry as eccentrics, and frankly there is still some debate as to precisely what mechanism is occurring during isometric tempo training. So the athlete can actually perform fairly more total work during eccentric-based training (even if it NEVER feels that way). Although eccentrics are notoriously known to induce greater residual soreness, the energy used during training is lower when compared to ISO’s or concentric muscle action. Additionally, eccentric muscle action actually expends a lower metabolic energy requirement, because some cross-bridges are forcefully detached due to the stretching of the muscle fiber, thus utilizing less ATP (3).
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In essence, the human body needs to be broken down and damaged before repairing and growth can occur, using eccentric tempos in training is a highly efficient way of amplifying this process and has been pretty much universally accepted as an effective training means in this regard. The physiological mechanism occurring during eccentrics is an induced mechanical stressor on the contractile properties- myofilaments and sarcomere (5). The belief on this is that due to the increased tension under load that occurs, fast twitch muscle fibers (type II fibers) are recruited earlier to accommodate, representing a reversal in the size principle (3). Another reason for this is that we are able to tolerate load more advantageously than we are able to produce force.
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What’s even more bizarre, is that every time the muscle spindle fibers or GTO’s transmit signals, the messages are sent to the brain and returned in under 0.01 seconds (2)! Takeaway point being, adding tempo work into your training will specifically target these proprioceptive bodies and retrain the central nervous system to stimulate and inhibit more adequately.īy biological default, we are generally stronger in eccentric muscle actions when compared to concentric, in part because we are working with, rather than opposing gravity. Both of these proprioceptive bodies are constantly at work and involved in any muscular action no matter the demand or complexity. GTO’s are the overbearing parent, who are well intended but intercede far more than they really need to. Think of GTO’s like having a brick under your gas pedal that’s strategically positioned to prevent you from going above 60 mph. Conversely, GTO’s, which are proprioceptive bodies found in the musculotendon junction detect changes in force and send signals to the brain to instruct the muscle to relax (1).
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Your muscle spindle fibers are proprioceptive bodies found in the muscle that detect changes in muscle length and send signals to the brain to tell the muscle how hard it needs to contract (1).
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The stretch reflex is one of the most powerful mechanisms of the human body and is the byproduct of the muscle spindle fiber stimulation minus the GTO inhibition the sensitivity, or conditioning of each is extremely important for resultant force production. When you boil it all down, force production is the result of the stretch reflex-GTO reflex (GTO = golgi tendon organs) (1). Quick Physiology 101 Interjection: Before I get into the specifics of eccentric and isometric training, I wanted to cover some quick noteworthy points on general neurophysiology to help clarify any potentially confusing points discussed.