Joe Collins

Many lifters rely on the sensation of muscle contraction to determine whether an exercise is effectively targeting that muscle. But how accurately does this subjective sensation reflect actual muscle activation? A new study provides interesting insights on the topic (PMID: 42958421) The researchers recruited 9 trained men who performed leg curls at three different hip flexion angles (0, 40, and 80 degrees). Each condition involved 5 sets of 10 repetitions at 70% of 1RM. Muscle activation was assessed using MRI-derived T2 responses before and after exercise. Participants also rated how strongly they felt their hamstrings contracting on a scale from 0 to 10 (10 = strongest sensation), separately for different regions of the medial and lateral hamstrings. Results indicated that the sensation of muscle contraction didn’t consistently correspond with the regional activation patterns observed on MRI. In other words, the regions where participants reported feeling the strongest contractions were not necessarily those exhibiting the greatest MRI-derived activation responses. The findings challenge the assumption that feeling a muscle contract more strongly necessarily indicates that it’s receiving a greater training stimulus. Some important caveats: First, MRI-derived T2 responses are indirect measures of muscle activation and don’t necessarily predict hypertrophy. Second, the subjective ratings grouped individual muscles into medial and lateral regions, preventing a direct muscle-by-muscle comparison with MRI responses. Third, the study did not instruct lifters to a specific attentional focus, so results can’t be generalized to mind-muscle connection. Finally, the study did not directly assess statistical correlations between perceived contraction and MRI responses were reported. This is an important distinction because observing different patterns between two measures is not equivalent to demonstrating that the measures are uncorrelated. Bottom line: We should be cautious about assuming that a stronger sensation translates into greater muscle activation. Whether it translates to better growth remains TBD. doi.org/10.1186/s13102-026-0…

Our recent meta-analysis (PMID: 39205815) suggests that inter-set rest intervals of approximately 90–120 seconds are needed to optimize muscle hypertrophy during intense resistance training. But this raises an important question: Are longer rest intervals inherently more conducive to muscle growth, or is their apparent advantage simply due to allowing a greater volume load to be performed? A study by Longo et al. (PMID: 35622106), in which I was a coauthor, sought to answer this question. We randomized 28 young, previously untrained participants perform resistance training twice weekly for 10 weeks, comparing 1-minute versus 3-minute rest intervals, with and without equating volume load (sets × reps × load). Results showed that when volume load differed between conditions, 3-min rest intervals produced ~13% growth in quadriceps muscle size, compared to ~7% with 1-min rest intervals. However, when volume load was equated, the advantage of longer rest disappeared, with both conditions producing similar gains. Collectively, the findings suggest that the hypertrophy advantage of longer rest intervals may be largely attributable to their ability to facilitate greater training volume, rather than the rest duration itself. Shorter rest periods can produce comparable muscle growth, but you may need to perform additional sets to compensate for the reduction in reps. The takeaway: Rest intervals are a tool, not a magic number. Longer rest periods can be a more efficient way to maintain training performance and accumulate volume, while shorter rests can also be effective when sufficient volume is achieved. A caveat: These findings were obtained in previously untrained individuals performing high-load leg presses. We can't necessarily generalize them to trained lifters or all exercises. ovid.com/jnls/nsca-jscr/full…