Electromyographic and Handheld Dynamometry Assessment of Lumbo-Abdominal Function in Elite Acrobatic Military Parachutists: An Exploratory Cross-Sectional Study.

BACKGROUND

Elite acrobatic military parachutists are exposed to extreme repetitive axial loads and high gravitational forces, and low back pain (LBP) is common; however, the relationship between LBP and trunk neuromuscular function in this population remains unclear. This study aimed to explore whether lumbar multifidus (LM) activation and the lumboabdominal strength ratio differ between parachutists with and without LBP.

MATERIALS AND

METHODS

This exploratory cross-sectional study assessed nine male elite Spanish Air Force acrobatic parachutists (mean age 31.2 ± 5.5 years; 3527.89 ± 2973.92 lifetime jumps). Participants were classified into two groups: those without LBP and those with current LBP or a history of LBP within the previous 6 months. LM activation was measured with surface electromyography (mDurance). Trunk flexor and trunk extensor isometric strength were measured with handheld dynamometry (HHD) (Lafayette Manual Muscle Tester), and the lumboabdominal strength ratio was calculated as abdominal strength divided by lumbar extensor strength. Between-group comparisons used Mann-Whitney U tests for continuous variables and Fisher's exact tests for categorical variables with Bonferroni correction; a two-sided probability value less than 0.05 was considered statistically significant.

RESULTS

LBP prevalence was 44.4% (4/9), and no sick leave due to LBP was reported. Groups did not differ in age, anthropometrics, lifetime jumps, daily energy expenditure, or sitting time (all probability values greater than 0.05). In the total sample, mean LM activation was 0.57% and 0.79% of the maximum voluntary isometric contraction (MVIC) at rest (left and right, respectively), and 34.34% and 34.47% of the MVIC during the functional task. The mean lumboabdominal strength ratio was 0.90. Effect sizes were negligible for basal multifidus asymmetry and the lumboabdominal strength ratio (δ = 0.00) and small-to-moderate for functional multifidus asymmetry (δ = 0.30), with no statistically significant between-group differences after Bonferroni correction.

CONCLUSIONS

In this homogeneous cohort of elite acrobatic military parachutists, low back pain was not associated with altered LM activation or lumboabdominal strength ratio as assessed by field surface electromyography and HHD. These findings are hypothesis-generating given the small sample size and support larger multicenter longitudinal studies incorporating dynamic and imaging-based assessments to clarify mechanisms and readiness implications.