Publications

Myoton Clarification Note: A Guide to Interpreting the Inverse Relationship Between Logarithmic Decrement and Tissue Elasticity

Objective: To investigate the acute and short-term (24 h) effects of localized plantar flexion fatigue on muscle mechanical properties, countermovement jump (CMJ) kinetics, and dynamic balance, focusing on recovery profiles of the gastrocnemius medialis (MG) and lateralis (LG).

Design: Prospective, repeated-measures experimental study.

Methods: Twenty-eight healthy volunteers (n = 28) performed a standardized unilateral isometric plantar flexion fatigue protocol until task failure (Borg CR-10 ≥ 8). Assessments were conducted at baseline, immediately post-fatigue, and 24 h post-fatigue (24 h). Outcomes included myotonometric properties (tone, stiffness, elasticity, relaxation time, and creep) of the MG and LG via MyotonPRO, CMJ kinetics via force plate, and dynamic balance via the Modified Star Excursion Balance Test (mSEBT).

Results: Significant Time × Region interactions were found for stiffness (P = 0.038, ηp² = 0.276) and relaxation time (P = 0.024, ηp² = 0.171). Both muscle heads showed an acute decrease in stiffness (P < 0.001); however, LG stiffness recovered by 24 h (P = 0.330), while MG stiffness remained reduced (P < 0.05). Although CMJ height recovered at 24 h (P = 0.842), eccentric and braking phase durations remained prolonged (P < 0.001; ηp² = 0.357 and ηp² = 0.264), indicating altered neuromuscular strategies. For dynamic balance, a delayed impairment was observed in anterior reach distance, which declined only at 24 h compared to baseline (P = 0.021, ηp² = 0.133).

Conclusion: Localized plantar flexion fatigue induces region-specific mechanical alterations and asynchronous recovery. Restoration of jump height at 24 h masks persistent deficits in eccentric phase durations and MG stiffness. These findings highlight a “neuromuscular vulnerability window” at 24 h post-fatigue, where delayed impairments in MG mechanics and anterior stability may increase potential susceptibility to injury despite apparent recovery. Practically, monitoring head-specific muscle mechanics, rather than global performance outcomes, is critical during this 24 h window to optimize training modification and guide objective return-to-play decisions.

Keywords: muscle mechanical properties, gastrocnemius, fatigue recovery, countermovement jump, mSEBT, myotonometry

Localized plantar flexion fatigue induces region-specific alterations in muscle mechanical properties and functional performance. A critical finding of this study is the regional heterogeneity in recovery: medial gastrocnemius (MG) stiffness remains significantly compromised at 24h, whereas the lateral head (LG) normalizes. Furthermore, the apparent recovery of vertical jump height at 24h masks persistent shifts in neuromuscular strategy, characterized by prolonged eccentric and braking durations.

The delayed impairment in mSEBT anterior reach further underscores a NVW that manifests well after acute fatigue has subsided. However, because this study was conducted on healthy, recreationally active young adults, these findings should be generalized to elite athletes or elderly populations with caution, as recovery kinetics and compensatory strategies may differ significantly. Clinicians, physical therapists, and coaches should not rely solely on global performance metrics like jump height; instead, they should monitor head-specific mechanical parameters and jump phase durations to accurately guide load management and mitigate the risk of lower-limb injuries during the post-fatigue recovery period. Future protocols must incorporate objective, muscle-specific myotonometric monitoring alongside functional metrics to ensure true physiological readiness.