Isometrics Basically Involve Applying Maximum Force to an Immovable Object
For example, stand in the middle of a doorway and press your arms into the door frame as if you were doing a lateral raise. Press against the door frame as hard as you can. Unless you are the Hulk, the door way is not moving and neither are your arms or your shoulder joints. But your deltoid muscles were still contracting as hard as possible. That is an isometric contraction.
When you do an isometric contraction you actually apply more force than any other time.
For example, when you do lateral raises, even if you went so heavy as your one-rep max, you were able to lift the weight. So your muscles only applied enough force to lift that weight. When you try to move an immovable object, your muscles apply even greater force (as long as you are pushing with your all-out effort) than when you lift a weight that’s equal to your one-rep max. That’s one reason why isometrics can help you to get stronger. However, the problem here is that isometrics only increase strength in that one joint angle. You can overcome this with a power rack on exercises such as the bench press or squat. Just change the height of the bar on the rack and you can do isometrics through the whole range of motion. And many powerlifters do this to increase their strength.
However, the study I am going to discuss used isometrics to increase muscle strength in an entirely different way.
Researcher from the University of Wisconsin – Parkside (Kenosha, WI) used isometrics on an antagonist muscle to make the agonist muscle stronger. Say what?!
Okay, a brief lesson on kinesiology.
Many muscles are referred to as agonist or antagonist muscles. When you do a barbell curl, the biceps is the agonist muscle, as it is the one performing the movement, which in this case is flexion of the elbow. The triceps, on the other hand, are considered the antagonist muscle, as they perform the exact opposite movement of the biceps. They extend the elbow joint, such as during triceps pressdowns. This is the same for the hamstrings and the quadriceps. When you extend at the knees, such as during leg extensions, the quadriceps are the agonist and the hamstrings are the antagonist.
The antagonist muscle actually makes the agonist muscle weaker.
For example, when you do leg extensions to work the quadriceps, the hamstrings (antagonist) are lengthened as the quadriceps contract (shorten) to extend the knees. The hamstrings resist this lengthening a bit and so the quadriceps not only have to work against the weight on the leg extension machine, but they also have to work against the hamstrings (which act like a rubber band that the quads must stretch).
If you fatigue the antagonist muscle before you work the agonist muscle, the resistance to the lengthening of the antagonist can be reduced because the antagonist muscle is too fatigued to put up much of a fight.
And that is what the University of Wisconsin researchers investigated. They fatigued the antagonist muscles with isometric contractions.
The researchers had subjects perform the vertical jump on a force plate to measure force production on two different occasions.
In one trial they had the subjects first do a six-second isometric leg curl to fatigue the hamstrings and then immediately perform the vertical jump. In another trial they just did the vertical jump without the leg curl first. In this case, the quadriceps are the primary agonist muscle and the hamstrings are the antagonist.
They reported at the 2011 Annual Meeting of the National Strength & Conditioning Association that doing the isometric leg curl first increased their quadriceps force production by almost 15%.
Jim’s take-home point.
Although this study used a power exercise, the vertical jump or jump squat, it is showing that when you first fatigue the antagonist muscle (hamstrings), it increases the force (power and strength) of the agonist muscle (quadriceps).
To use this technique in the gym, perform a superset by first doing a 5- or 6-second isometric contraction of the antagonist muscles of the muscle group you are training and then immediately perform the exercise that targets the agonist muscle.
The best position to hold the isometric contraction is about the halfway point of the range of motion of that exercises. For the bench press try isometric rows, for curls try isometric triceps pressdowns, for shoulder presses try isometric pulldowns, and for leg extensions try isometric leg curls and the opposite applies as well.
Reference:
Ebben, W. P., et al. Antagonist knockout training increases force and the rate of force development. Annual Meeting of the National Strength & Conditioning Association, 2011.
