Muscle alterations induced by electrostimulation are lower at short quadriceps femoris length.
Level 2 - randomized trial
Randomized within-subject contralateral controlled trial
PubMed 31807900 · doi:10.1007/s00421-019-04277-5
What was done
Ten healthy participants completed two neuromuscular electrical stimulation (NMES) sessions consisting of 40 isometric knee extensor contractions. In a randomized within-subject design, one knee was stimulated at 50 degrees flexion (short quadriceps length) and the contralateral limb at 100 degrees flexion (long quadriceps length). Muscle damage markers—including maximal voluntary isometric contraction (MVC) force, muscle volume, and MRI transverse relaxation time (T2)—were evaluated pre-exercise and at 2 (D2), 4 (D4), and 7 (D7) days post-session.
What was found
At identical stimulation intensities, peak evoked force during the NMES session was higher at short muscle length (61 ± 12% MVC) than at long muscle length (30 ± 5% MVC). In subsequent days, voluntary MVC force was significantly reduced from D2 to D7 in the long-length limb, whereas no significant change occurred in the short-length limb. Similarly, MRI-derived muscle volume and T2 increased at D2, D4, and D7 in the long-length limb, but showed no change in the short-length limb.
Why it matters
Applying NMES at a shorter muscle length allows greater force production during stimulation while preventing the prolonged muscle damage and strength decrements caused by stimulation at longer muscle lengths.
Limits
The study had a very small sample size (n = 10) restricted to young, healthy participants, limiting direct generalizability to clinical rehabilitation cohorts. The abstract does not report specific numerical values for soreness ratings, muscle volume changes, or T2 alterations.
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