Author(s): DOMROES, T., WEIDLICH, K., BOHM, S., MERSMANN, F., ARAMPATZIS, A., Institution: HUMBOLDT-UNIVERSITÄT ZU BERLIN, Country: GERMANY, Abstract-ID: 700

INTRODUCTION:
Imbalances between muscle strength and tendon stiffness can increase the mechanical demand on the tendon (i.e., tendon strain) and tendon injury risk (1). The early identification of musculotendinous imbalances and accordingly adjusted training may thus contribute to tendon injury prevention (2). Therefore, the aim of the study was to identify muscle-tendon imbalances in athletes and promote a more balanced adaptation of muscle and tendon through a personalized assessment and loading concept.
METHODS:
A total of 85 athletes (37 female and 26 male adolescents (13 – 16 yrs.), 22 male adults) were assigned to a control and intervention group. We assessed knee extensor muscle strength, patellar tendon stiffness and strain during maximum isometric contractions (MVC) at four measurement time points during a competitive season. Muscle-tendon imbalances were identified based on the individual tendon strain during MVCs (2). In the intervention group, athletes with deficits in tendon stiffness (strain ≥9%) performed exercises (3x/week) with a personalized load to reach ~5.5% tendon strain to promote tendon adaptation, athletes with deficits in muscle strength (strain ≤4.5%) trained with submaximal loads to failure to mainly promote muscle strength. Linear mixed-effects models were used to analyze time- and group-dependent developments and the influence of sex and age.
RESULTS:
We found lower fluctuations of maximum tendon strain (p = 0.016) and a decrease in the frequency of athletes with high-level tendon strain ≥9% in the intervention group. Normalized tendon stiffness and muscle strength increased significantly over time only in the intervention group (p < 0.001). These increases were more pronounced in male compared to female adolescents (sex by time by group interaction; p = 0.010 and 0.002). In adults we found a more pronounced increase in tendon strain in the control group compared to male adolescents (age by time interaction; p = 0.040) paralleled by a more pronounced increase in muscle strength (age by time by group interaction; p = 0.010).
CONCLUSION:
The reduced fluctuations of maximum patellar tendon strain over the season and the lower prevalence of highly increased maximum tendon strain in both age groups and sexes indicate that the presented personalized concept was effective in reducing muscle-tendon imbalances and has the potential to contribute to tendon injury prevention, given the increased injury risk associated with high-level tendon strain. The smaller increases in muscle strength and tendon stiffness in females may suggest sex differences in muscle and tendon adaptation, which, however, did not affect the reductions in strain fluctuations and high-level tendon strain, and thus the effectiveness of the personalized concept.
REFERENCES:
1) Mersmann et al., 2023, Sports Med – Open 9:83
2) Arampatzis et al., 2020, Front. in Physiol. 11:723