|Find out what's taking you from PR to PR, is it an increase in muscle size or activation on how important is how strong you already are?|
The British scientists got to the bottom of your gains by assessing the individual and combined contribution of the adaptations in neural (agonist quadriceps EMG, antagonist hamstring EMG) and morphological (quadriceps muscle volume and θp, the fascicle pennation angle) variables.
Based on the data from their 12-week study in twenty-eight healthy young men, who had not completed lower body RT for >18 months and were not involved in systematic physical training, the scientists were able to calculate the individual contribution of the previously named variables and the trainees' baseline strength on the effect of the following workout:
"After a brief warm-up of submaximum contractions of both legs, participants completed four sets of ten unilat eral isometric knee extensor contractions of each leg; with sets alternating between dominant and non-dominant legs. Each set took 60 s with 2 min between successive sets on the same leg" (Balshaw 2017).To differentiate potential interference with explosive vs. sustained contractions, the participants were further randomized to two groups:
- the explosive contraction group completed short, explosive contractions with participants instructed to perform each contraction “as fast and hard as possible” up to ≥80% MVT for ~1 s, and then relax for 5 s between repetitions.
- the sustained contraction group completed prolonged contractions at 75% MVT, with 2-s rest between contractions.
As Balshaw et al. point out, their results are in line with other EMG studies assessing the effect of training on the lower extremities. What is interesting, however, is that they conflict with a study by Erskine et al. (2014) who found only a marginal correlation between improved activity patterns and strength gains for the biceps a muscle with an already high level of activation even in untrained individuals.
This result is important for our prediction because it suggests that a higher baseline activation level will reduce the contribution of improvements in agonist neural drive to the strength gains. This, in turn, obviously suggests that, in trained individuals who have already undergone significant improvements in neural drive, muscle activity will contribute significantly less to the strength gains than it does in untrained individuals. An equivalent to Figure 3 for well-trained athletes may thus look as I have sketched it in the figure on the left-hand side: Hypertrophy could make the largest, while improved muscle activation, only a marginal contribution to strength gains - but keep in mind: that's just an educated guess that is based on the assumption that the relative contribution of hypertrophy will increase as the relative contribution of improvements in muscle activation patterns will decrease over time (Note: Whether the three variables will then still explain 60% of the variation appears questionable, though; thus the 10% reduction in total predictive power in the figure above).
- hypertrophy contributes quasi-linearly to the gains (Figure 1 A) - I would estimate the reciprocal of the slope of the linear regression line to be ~2.5, meaning for each 1 % increase in muscle volume there was a 2.5% increase in maximal voluntary torque;
- agonist activity changes contribute quasi-linearly to the gains (Figure 2 A) - I would estimate the reciprocal of the slope of the linear regression line to be "only" ~0.8, meaning for each 1% increase in muscle activity there was a 0.8% increase in maximal voluntary torque;
- pre-training strength negatively predicts the strength gains (Figure 2 C) - What may sound odd, initially, is actually only logical. The stronger you are at baseline, the lower your strength gains are going to be. For this relationship, I would estimate the slope of the linear regression analysis to be approx. -1.5, which means that for each extra Newton-metre (nM) of pre-training maximal voluntary torque, the increase in response to training will be reduced by 1.5%;
- pennation angle and antagonist activity changes do not contribute clearly to the strength gains (Figure 1 B, Figure 2 B) - you know that because there was no clear correlation between the corresponding variables in the regression analysis the scientists did
So, there's clear evidence that size gains (hypertrophy), muscular activation (EMG) and, of course, the baseline strength determine the strength gains in resistance training rookies.
- Balshaw, Thomas G., et al. "Changes in agonist neural drive, hypertrophy and pre-training strength all contribute to the individual strength gains after resistance training." European Journal of Applied Physiology (2017): 1-10.
- Erskine, Robert M., Gareth Fletcher, and Jonathan P. Folland. "The contribution of muscle hypertrophy to strength changes following resistance training." European journal of applied physiology 114.6 (2014): 1239-1249.