NEW: Changes in Early and Maximal Isometric Force Production in Response to Moderate- and High-Load Strength and Power Training

Comfort, Paul; Jones, Paul A., Thomas, Christopher; Dos'Santos, Thomas; McMahon, John J.; Suchomel, Timothy J.


Journal of Strength and Conditioning Research: March 2022 - Volume 36 - Issue 3 - p 593-599doi: 10.1519/JSC.0000000000003544


PURPOSE:

To determine the changes in 1) isometric force production at 50, 100, 150, 200, 250 milliseconds (ms) and 2) maximal isometric force production following a 4-week period of moderate-load (60 to 82.5% of a 1-RM) resistance training, then another 4-week period of high-load (80 to 90% of a 1RM) resistance training.


Force production results were measured using two exercises: 1) an isometric mid-thigh clean pull and 2) a 1-RM power clean.


The exercises used during each of the 4-week periods were:

Back squat

Power clean

Negative Nordic hamstring curl

Mid-thigh clean pull

Romanian dead lift

Push press


RESULTS:

Only minimal to moderate changes in isometric force production in ms were observed in response to the moderate-load training period.


Much larger increases in isometric force production in ms were observed in response to high-load training.


There was a very large increase in peak force (PF) during the moderate-load phase, but only a moderate increase in PF during the high-load phase.


High-load multi-joint resistance training results in superior increases in multi-joint force production in the initial ms as compared with the changes noted following moderate-load resistance training.


IN PLAIN ENGLISH:

In respect to the force-velocity curve, the greater the force generated, the lesser the velocity.


In the case of isometric force, there is no velocity because there is no displacement of the load. However, a high level of force can be generated (and measured) isometrically due to the load being stationary.


Therefore, a greater amount of force can be generated quickly (in ms) using a high load that does not move very fast.


The amount of peak force generated with a moderate-load can also be high - not initially but over more ms - due to the high-effort exuded to move the relatively lighter load.