Early sub-maximal quadriceps motor unit firing characteristics and six-month knee extensor strength after anterior cruciate ligament reconstruction: a prospective longitudinal study.

Authors

Rob Buhmann, Abram Reeves, Daniel Mellifont, Max Stuelcken, Mark Sayers, David N Borg, Steven Lawrie

Published in

Annals of medicine. Volume 58. Issue 1. Pages 2740295. Epub Sep 28, 2026.

Abstract

To determine whether quadriceps motor unit firing rates measured pre-operatively and during the first three months after anterior cruciate ligament (ACL) reconstruction are associated with isometric knee extensor strength at six months, and to explore the relationship between motor unit action potential (MUAP) amplitude and firing rate.
Twenty-seven participants (15 female) underwent surface electromyography of vastus medialis and vastus lateralis during sub-maximal isometric knee extension from pre-operation to three months post-reconstruction. Six-month knee extensor MVC force was modelled using Bayesian regression and interpreted using a region of practical equivalence (ROPE; ±15 N). A secondary hierarchical analysis examined MUAP amplitude and firing rate.
Motor unit firing rate was not consistently associated with six-month knee extensor strength across time points and limbs. In the ACL reconstructed limb at two weeks, a 1-SD greater mean firing rate was associated with 45.8 N greater six-month strength (95% credible interval [CrI] - 18.5 to 114.6 N). Six-month strength was greater in the contralateral limb (β = 198.4 N, 95% CrI 171.6 to 225.1 N), in males (β = 184.3 N, 95% CrI 32.0 to 325.1 N), and with greater body mass (β = 119.9 N per 1-SD, 95% CrI 33.4 to 207.2 N). Greater relative MUAP amplitude was associated with lower firing rate (-3.7 Hz per 1-SD, 95% CrI -3.8 to -3.6 Hz).
Sub-maximal quadriceps motor unit firing rate was not consistently associated with later knee extensor strength, although a stronger positive association was suggested in the reconstructed limb at two weeks. Firing rate was strongly related to relative MUAP amplitude, and its predictive value for later strength appears limited.

PMID:
42804596
Bibliographic data and abstract were imported from PubMed on 29 Sep 2026.

Read full publication at:
Please sign in to see all details.

Stats

1-terrible, 9-excellent. How would you rate this publication? Sign in in to submit your rating.

Post a comment

You need to be signed in to post comments. You can sign in here.

Comments

There are no comments yet.