Interlimb differences in gait kinematics, kinetics, and muscle activation during walking and running one year after acute unilateral Achilles tendon rupture.

Background: Approximately 30% of individuals with Achilles tendon rupture do not fully restore normal gait function, regardless of the treatment chosen. Limited knowledge exists about the long-term kinematic, kinetic, and neuromuscular adaptations after repair of an acute Achilles tendon rupture and their impact on muscle/tendon function. This exploratory cross-sectional study assessed between-limb differences in terms of lower-limb kinematics, kinetics, and muscle activation during walking and jogging stance phases one year after an Achilles tendon rupture.

Methods: Thirty-seven participants (29 males, 8 females; mean age 47.4 ± 9.4 years) were included in the study one year after Achilles tendon rupture, who were both operatively and non-operatively treated. Electromyography (EMG) was recorded synchronously with kinematic and kinetic data using an optical motion capture system with a cluster-based marker set allowing six degrees of freedom. Bilateral EMG was collected from the tibialis anterior, medial and lateral gastrocnemius, and soleus muscles. The stance phase was divided into initial contact to mid-stance (IC-MS) and mid-stance to toe-off (MS-TO). Differences between affected and unaffected limbs were analyzed with multivariate normal models, reporting point estimates and 95% credible intervals.

Results: During walking, triceps surae activation increased in MS-TO, while running showed greater activation in IC-MS. Affected limbs showed higher lateral gastrocnemius activation during walking IC-MS (2.1 EMG%; CI: 0.5-3.7) as well as greater medial (3.4%; CI: 0.5-6.3) and lateral (4.9%; CI: 2.3-7.6) activation in MS-TO. Ankle sagittal joint excursion was reduced in walking MS-TO (-1.8°; CI: -2.8 to - -0.8) and running MS-TO (-4.1°; CI: -5.8 to -3.5), with decreased sagittal plantarflexor moments during running (0.06 Nm/kg: CI: 0.01-0.11).

Conclusion: One year after Achilles tendon rupture, walking was characterized by increased gastrocnemius muscle activation and reduced ankle sagittal joint excursion compared with the unaffected side. Moreover, running also showed reduced ankle joint excursion accompanied by attenuated plantar flexor moments, however, without any evident side-to-side differences in EMG recordings. Despite the observed inter-limb deficits, gait resembled normative kinematic patterns, likely reflecting compensatory mechanisms. EMG and joint moments were more variable than kinematics. These results support the need for individualized targeted long-term triceps surae rehabilitation following Achilles tendon rupture.