Training to Failure and Modifying Rest Times: Two Ways to Maximize Muscle Activity? Two Studies, Similar Implications
|This is what science looks like... Well, at least in the Hiscock study, where the subjects, 10 young men with at leas 12 months of training experience did regular and hammer dumbbell curls on the preacher bench - (photo | Hiscock. 2015).|
If you believe in what you can read in many articles on strength training, both, training to failure and decreasing rest times / drop sets should significantly increase the muscle activity and thus - this is the most important thing - the number of motor units that are recruited during the exercises.
But is this actually true? I mean, is there a link between EMG activity, the number of motor units that are firing and the way you train? I guess, it would be wise to take a brief look at the pertinent research before we get to design and results of the individual studies. So, what do we have? As Looney et al. point out, motor unit activity can be measured through electromyography (EMG) which is commonly considered to reflect the neural drive to the muscle. Since the electrical impulse should be proportional to the number of motor units that are firing and in view of the fact that the latter determines the acute force output, it should be obvious that increasing force demands result in higher EMG amplitude due to the greater recruitment of motor units and faster firing rates necessary to increase the contractile force.
|Figure 1: Previous studies show that the motor unit recruited (or at least it's indicator, the mean EMG values) increases over the duration of sustained or repeated muscle actions at a constant force level (Masuda. 1999 - l; Mottram. 2005 - r)|
Why is it even important that all muscle fibers contract? The reason should be obvious, but I am happy to explain it once more. It is the contraction that's responsible for the exercise induced increase in GLUT-4 receptor expression and mTOR phosphorylation. In view of the fact that the latter determine the increase in glucose uptake and protein synthesis after a workout, you obviously want as many muscle fibers to contract as possible. Or, to put it differently: If you don't use it you won't grow it, bro... well, at least not to the same / optimal extent.This is where the "train to failure to maximize motor unit recruitment"-theory comes from. After all, this observation indicates that usually inactive motor units are going to fire only during prolonged training at high intensities (best to failure). As usual, though, there are problems with this theory:
"While the increase in EMG amplitude observed during repeated muscle actions has been explained by increased central drive necessary to sustain force as fatigue accumulates, it is inconclusive whether fatigue derived from earlier performed exercise induces greater EMG amplitude during subsequent exercise. Previous studies have shown EMG amplitude diminishes after strenuous resistance exercise protocols. In contrast, Smilios et al. demonstrated progressive increases in EMG amplitude over a series of 20-repetition sets with gradually decreasing resistance interspaced with 2-minute rest periods. Further uncertainly exists pertaining to consecutive maximal effort sets with progressively lighter resistance performed without allotted rest periods. This frequently incorporated training technique, commonly known as a “drop set”, has remained relatively uninvestigated" (Looney. 2015).Needless to say that we all expect that lighter weights can stimulate greater motor unit recruitment, if you use them in dropsets, but as Looney et al. say, the science that would conclusively confirm that is simply not there (yet). The goals of Looney's study were thus as follows:
- Firstly, confirm / refute the assumption that EMG amplitude would be significantly greater in light resistance exercise (50% 1RM) performed in rested conditions to a maximal number of repetitions than to a submaximal number of repetitions.
- Secondly, assess whether the EMG amplitude would be significantly lower in maximal repetition sets performed in rested conditions with 50% 1RM resistance than with heavy resistance (90% 1RM).
- Thirdly, test whether the EMG amplitude would be greater in maximal repetition 50% 1RM resistance sets performed in pre-fatigued conditions (no prior rest period) than in rested conditions.
|If you don't do them as an intensity add-on / finisher don't do partial reps at all - "Full Rom, Full Gains" | more|
- A drop set day, on which he subjects performed three consecutive maximal repetition sets at 90%, 70%, and 50% 1RM to failure with no rest periods in between.
- A single set day, on which the subjects performed a maximal repetition set at 50% 1RM to failure (no "dropping" involved).
|Figure 2: Very general summary of the research interests and designs of the two studies discussed in today's SuppVersity article by Looney et al. (2015) and Hiscock et al. (2015)|
|Figure 4: Mean number of repetitions (left, top), rate of perceived exertion (RPE | left, bottom), and peak EMG amplitude as a measure of motor recruitment (Looney. 2015).|
- 3 sets × 8 repetitions × 120 s recovery between sets;
- 3 sets × 8 repetitions × 240 s recovery;
- 3 sets × maximum number of repetitions (MNR) × 120 s recovery;
- 3 sets × MNR × 240 s recovery.
|Figure 5: Despite sign. higher volumes (see boxes) and a 100% increase in rate of perceived local muscular exertion there was no significant increase in muscle activity with lifting 70% of the 1RM for 8 vs. to failure (Hiscock. 2015).|
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