The Claim
In untrained males performing knee extension exercises to muscular failure at 50–60% of their one-repetition maximum (1RM), a repetition duration of 2 seconds results in higher normalized electromyographic (EMG) amplitude in the rectus femoris and vastus lateralis muscles across most of the concentric range of motion (100–40° knee flexion) compared to a 6-second repetition duration, except at the end range (40–30°), where the 6-second protocol elicits greater muscle activation, suggesting that movement speed influences neuromuscular recruitment patterns during dynamic resistance exercise.
What the research says
Challenges is higher
Challenge is ahead, but a single strong supporting study can change this.
These are independent scores, not a percentage. Higher-grade studies count more, so a single strong opposing study can outweigh several weaker ones.
When untrained guys do leg extensions with a medium weight until they can't do any more, moving faster (2 seconds per rep) makes their quads work harder for most of the movement — but moving slower (6 seconds per rep) makes them work harder right at the end. So, how fast you lift changes which part of the move your muscles feel most.
See the scientific wording
In untrained males performing knee extensions to failure at 50–60% 1RM, a 2-second repetition duration protocol is associated with higher normalized electromyographic (EMG) amplitude in the rectus femoris and vastus lateralis muscles across most of the concentric range of motion (100–40°) compared to a 6-second protocol, except at the end range (40–30°), where the 6-second protocol shows greater activation, indicating movement speed modulates neuromuscular recruitment patterns.
What the research says
1 studyThe study looked at the same type of exercise and speeds as the claim, but it didn’t measure muscle activity in enough detail to confirm whether faster or slower reps caused more muscle activation at specific knee angles.
Score breakdown, mechanism chain, raw evidence, ideal studies needed & 1 supporting studies
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.