As a performance coach, I view isometric training as the essential bridge between eccentric and concentric muscle actions—an often overlooked phase that unlocks tissue resilience, neurological adaptation, and deeper muscular control.
Let’s break it down:
The Eccentric Phase – The Engine of Muscle Remodeling
Eccentric contractions: where the muscle lengthens under tension, are the driving force behind structural adaptation. This is the phase most responsible for the microscopic tearing of muscle fibers, which initiates protein synthesis and, ultimately, hypertrophy and strength gains. Research supports this: studies have shown that eccentric loading produces significantly more muscle damage and results in greater increases in muscle size and strength compared to concentric-only training (Roig et al., 2009).
Think of eccentrics as the engine room of muscle development. For instance, if your one-rep max (1RM) on the bench press is 315 lbs, attempting a 4–5 second controlled eccentric at that load would be nearly impossible without failure. However, by training at 60% of your 1RM (around 190–205 lbs) with a 3–5 second tempo on the descent, you can create high levels of muscular tension, push close to failure, and still limit the wear and tear associated with maximal effort lifts.
The Concentric Phase – The Expression of Force
Concentric actions represent the shortening phase of a muscle contraction the “go” phase where force is expressed. This is where peak motor unit recruitment occurs, allowing us to measure and express strength and power. Take the top end of a bicep curl: that peak contraction is concentric. The eccentric portion occurs as we lower the weight, and if we were to pause mid-rep and hold, we’d enter the isometric phase.
Isometrics – The Bridge and the Base
Before jumping headfirst into aggressive eccentric or concentric work, isometric training offers a safe and effective foundation. Isometrics build positional strength, enhance tendon stiffness, and improve joint integrity—making them an ideal starting point for both athletes and general populations. A 2021 review published in Sports Medicine showed that isometric training can increase maximal strength and rate of force development, particularly when performed at longer muscle lengths (Oranchuk et al., 2019).
Isometrics also provide a neurologically rich stimulus without high mechanical fatigue, which is especially valuable during in-season training or rehabilitation. From mid-rep holds to yielding and overcoming isometrics, these methods drive both stability and strength.
Final Thoughts
Every phase of muscle action matters. Eccentrics lay the groundwork for growth, Concentrics express that strength, and isometrics fortify the bridge between them. If we begin with isometrics, we build tissue tolerance, muscular awareness, and a neural foundation that makes both eccentric and concentric work more effective. It’s not just about lifting heavier—it’s about training smarter, with intent and integration.
“Isometrics are the foundation for developing stability and force at specific joint angles, where power is most often generated.”
— Brett Bartholomew, Performance Coach
