Author(s): HAUSER, L., SCHROLL, A., ARAMPATZIS, A., Institution: HUMBOLDT-UNIVERSITÄT ZU BERLIN, Country: GERMANY, Abstract-ID: 524

INTRODUCTION:
Perturbation-based exercise interventions can improve muscle strength and reduce low back pain intensity (1,2). It is suggested that the exposure to perturbations leads to an increase in muscle activation and specific modulations in motor control which improve the ability of the sensorimotor system to cope with perturbations. However, there is a lack of experimental data to support this assumption. Therefore, the current study aimed to investigate the effects of perturbations on muscle activation and modular organization of trunk and leg muscles during a functional exercise.
METHODS:
Twenty healthy participants (height 175.96 ± 9.27 cm, body mass 71.89 ± 13.25 kg, age 29.55 ± 7.21 years) performed a series of loaded back squats under four different conditions. The loaded back squats were either unperturbed (NP), perturbed unilateral using unstable ground (UGP) or unstable load (ULP) or perturbed bilateral (BP) combining unstable ground and load. Ground reaction forces, joint kinematics, and the electromyographic (EMG) activity of 14 trunk and leg muscles (bilateral) were recorded. We extracted muscle synergies using non-negative matrix factorization and analyzed the data with statistical parametric mapping and linear mixed models.
RESULTS:
Perturbations significantly (p<0.05) increased the velocity of the center of pressure (CoP) with concomitant adjustments in ankle-, knee- and hip-joint kinematics. When compared to NP, the EMG activity of most leg muscles was significantly increased (p<0.05) in BP and UGP, while most trunk muscles showed an increased EMG activity (p<0.05) in BP and ULP. Four fundamental synergies were detected among all conditions. However, we found alterations within the basic activation patterns of the muscle synergies due to the perturbed conditions. In two synergies the full width at half maximum (FWHM) of the temporal components was significantly (p<0.05) reduced during the perturbed conditions, while in one synergy the center of activation (CoA) was shifted towards an earlier time point (p<0.05).
CONCLUSION:
The higher muscle activation and CoP velocity indicate an enhanced demand for the sensorimotor system to perceive sensory signals and to generate appropriate motor commands during the perturbed back squats. The recruitment of the same number of muscle synergies in both perturbed and unperturbed conditions indicate a robust neuromotor control during loaded back squats. However, the adjustments in the temporal structure (i.e. changes in FWHM and recruitment time) of the muscle synergies during the perturbed back squats may facilitate the ability of the sensorimotor system to deal with perturbations and may contribute to the reported effectiveness of perturbation-based exercise interventions on the therapy and prevention of low back pain (1,2).
REFERENCES:
(1) Arampatzis et al., Eur J Appl Physiol, 2107
(2) Arampatzis et al., Transl Sports Med, 2020