Toe Flexor Muscle Strength in Vocational Ballet Dancers: Reliability,Variability,and Minimal Detectable Change of a Custom-Made Dynamometer

Abstract

Background: Toe flexor strength, which involves the combined activation of plantar intrinsic and extrinsic foot muscles, is crucial for locomotion, balance, and performance. Strong toe flexors are particularly crucial for efficient propulsion during running and jumping. Therefore, strengthening the feet has gained increased attention in the general population, as well as among athletes and dancers. However, accurately assessing foot muscle strength remains challenging. This study investigated the within- and between-session reliability of toe flexor maximal voluntary isometric contraction (MVIC) using a custom-made dynamometer. Method: Twenty-five vocational ballet students (23 females and two males; age: 16.48 ± 1.2 years; mass: 53.06 ± 8.84 kg; height: 167.14 ± 6.4 cm; forefoot length: 6.55 ± 0.44 cm) participated in two data collection sessions 48 to 72 hours apart with three trials each session. The toes were positioned at a 25° dorsiflexion angle on the dynamometer. Results: Between-session reliability showed good to excellent intraclass correlation coefficient (ICC) values for absolute MVIC (aMVIC) of the right and left foot (ICC = 0.89-0.95; 95% CI: 0.75-0.96; coefficient of variation [CV]: 4.63-6.45). Toe flexor strength normalized to forefoot length and body weight (rTFS) was excellent for both feet (ICC = 0.91-0.95; 95% CI: 0.79-0.98; CV: 4.8-6.4). The minimal detectable change (MDC) ranged from 9.7% to 13.7% of individual scores. Within-session ICC values ranged from 0.92 to 0.95 (95% CI: 0.70-0.98), indicating excellent reliability across all measures. Discussion: Based on these findings, we recommend conducting at least one familiarization session and three trials per session to reduce the variability in toe flexor muscle strength measurements. The toe flexor dynamometer shows great potential for future research on toe flexor muscle strength in dancers, as well as monitoring back-to-stage rehabilitation progress and assessing pointe readiness.