Quote[/b] (Blade @ Feb. 25 2003,1:51)]
Using EMG to determine how effective an exercise is
EMG reflects the level of "electrical" activation of the muscle. As such it is a good indicator of how hard a muscle is contracting. However, it isn't perfect. Having done EMG research myself while in school (Ex phys labs) I know that there are inherent weaknesses to the methods. Nevertheless, if you want to know how much electrical activity is going on in a muscle (or at least a certain part of that muscle), EMG is the best we've got.
In a very real sense, EMG is a result of voluntary effort. So, the harder you try to contract the muscle, the greater EMG activity you will see, regardless of how heavy it is. This brings in a great deal of between-subject, and between-trial error in measurements.
EMG is also greatly affected by practice or coordination. A person who is not well practiced at a given exercise will often display erratic EMG read outs.
Fatigue also changes EMG readouts. The more fatigue there is, the greater the EMG amplitude.
Keep in mind as well that during eccentric contractions, EMG amplitude goes down significantly, yet at the same time, the eccentric portion of an exercise presents a greater stimulus for growth than the concentric portion.
EMG as a tool specifically relating to bodybuilding (muscle growth) is not an accurate indicator of the efficacy of a given exercise to induce growth. The efficacy of any exercise is determined by the load, the duration, and the condition of the tissue at the time the load is applied.
For the lats, the load is limited by your strength level and degree of stretch during loading. The duration is limited by your “strength-endurance”, and time in the stretched position. The condition of the muscle is determined by what you have done with your lats in the last 6 weeks or so.
So, speaking in general (i.e. simplified) and acute (i.e. one training session) terms, the heavier any lat exercise becomes, the more effective it will become. The more volume you do at that weight, the more effective that session will be. The greater the stretch experienced by the lat and the longer you hold it, the more effective that exercise will be. And finally, the longer its been since you trained your lats, the more effective that session will be.
On a personal note, nothing has been as effective as the weighted eccentric chins/pull-ups at the end of an HST cycle for putting on real thickness on my lats.
- Bryan