In Part 1 of this series, we reviewed the research behind triphasic training. In Part 2, we discussed the eccentric phase. In Part 3, we'll examine the isometric phase—the phase in which absorbed eccentric energy turns into explosive, concentric actions.
Isometric actions are ones in which the muscle attachments closest and furthest from the center of the body (proximal and distal) remain at a constant length. You reach the isometric phase when the force you're exerting equals the force of the load.
Because the isometric phase is actually a contraction, it's trainable just like every other muscle action. Same as the eccentric phase, the isometric phase has two neurological processes that need to be trained to maximize the force transfer from the eccentric to concentric contractions. When muscles need to increase their level of force production, like they do when they decelerate and stop an eccentric contraction, they have two options:
Motor unit recruitment: Increase the number of muscles fibers that fire.
Rate coding: Increase the rate at which each fiber fires, which increases muscular tension.
Again, these physiological processes are outside the scope of this article. Just understand they are important to developing force. When you look at Figure 1, this becomes apparent. At some point on the graph, both lines have a transition point—a point where the line changes from a negative, eccentric slope to a positive, concentric one. That exact point is where the isometric contraction takes place. It is not like the eccentric phase, which has an entire line you can see and follow. Yet this single point is hugely important, because it acts as the springboard that launches the force from the stretch reflex and stretch-shortening cycle into the concentric contraction. The harder the stop, the better the total force recoil and the more explosive the action.
Specific attention to isometric training will result in improved force and power outputs for an athlete. Improving the qualities of the nervous system in this regard allows for high amounts of energy to be absorbed, diverting maximal energy from the eccentric directly to the concentric with little to no loss of energy. This enables an athlete to maximize the power of both the stretch reflex and the stretch-shortening cycle. Add these to a strong, concentric contraction, which we will learn about in the next part of this series, and you'll feel like you're jumping off a trampoline instead of out of a sand pit.
Perform high-load isometrics at the beginning of your workout. Isometric contractions aren't as neurally taxing as eccentric training. As a result, lightened-load isometrics can, and should, be used throughout the entire workout. When I say "lightened," I mean assistance lifts—exercises that use lighter loads compared to large compound movements, such as Lunges or Closed-Grip Bench.
Stay safe and get the best results by following four rules during your isometric work.
1) Hit the ground like a brick.
When performing a resisted-load isometric, move through the eccentric portion quickly, pulling the bar down before trying to instantly stop its momentum. You must hit the isometric like a brick hitting a pavement floor—no give whatsoever!
2) Squeeze your muscles.
Squeeze your muscles as you hit the isometric contraction. For example, if you're performing a Back Squat, squat down to where you will be performing the isometric contraction during your sets. Once you have squatted down, squeeze your legs and glutes as hard as possible for several seconds. Once you experience what the isometric contraction feels like, you can begin your work sets.
3) Always use a spotter.
During triphasic training, your body will be reach maximum fatigue. Since your muscles could give out at any time, it is crucial that you use proper spotting.
4) Always finish an isometric-focused lift with an explosive, concentric movement.
By incorporating an explosive movement at the end of your lift, you're training your nervous system. Check out Part 2 for a full explanation of this recommendation.
The following tables provide data on various isometric exercises. Check below for hyperlinks to videos that show how to properly perform each exercise.
Dumbbell Walking Lunge
Bench Press Reactive Drop Pause Toss
Bench Press Rack
Hip Flexor Isometric Prone
Single-Leg Isometric Deadlift
Isometric Ball Groin Squeeze
Hex-Bar Isometric Deadlift
Stay tuned for the final installment of this four-part series, on the concentric phase. For more great training tips, check out Triphasic Training: A systematic approach to elite speed and explosive strength performance.
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