Functional assessments of foot strength: a comparative and repeatability study.

BACKGROUND: Evaluating the strength of the small muscles of the foot may be useful in a variety of clinical applications but is challenging from a methodology standpoint. Previous efforts have focused primarily on the functional movement of toe flexion, but clear methodology guidelines are lacking. A novel foot doming test has also been proposed, but not fully evaluated. The purposes of the present study were to assess the repeatability and comparability of several functional foot strength assessment techniques. METHODS: Forty healthy volunteers were evaluated across two testing days, with a two-week doming motion practice period between them. Seven different measurements were taken using a custom toe flexion dynamometer (seated), custom doming dynamometer (standing), and a pressure mat (standing). Measurements from the doming dynamometer were evaluated for reliability (ICCs) and a learning effect (paired t-tests), while measurements from the toe flexion dynamometer and pressure mat were evaluated for reliability and comparability (correlations). Electromyography was also used to descriptively assess the extent of muscle isolation in all measurements. RESULTS: Doming showed excellent within-session reliability (ICCs > 0.944), but a clear learning effect was present, with strength (p < 0.001) and muscle activity increasing between sessions. Both intrinsic and extrinsic muscles were engaged during this test. All toe flexion tests also showed excellent reliability (ICCs > 0.945). Seated toe flexion tests using the dynamometer were moderately correlated to standing toe flexion tests on a pressure mat (r > 0.54); however, there were some differences in muscle activity. The former may better isolate the toe flexors, while the latter appeared to be more functional for many pathologies. On the pressure mat, reciprocal motion appeared to display slightly greater forces and reliability than isolated toe flexion. CONCLUSIONS: This study further refines potential methodology for foot strength testing. These devices and protocols can be duplicated in the clinic to evaluate and monitor rehabilitation progress in clinical populations associated with foot muscle weakness.

The Role of the Midfoot in Drop Landings.

PURPOSE: The midfoot is instrumental to foot function; however, quantifying its roles in human movement has been difficult. A forceful dynamic activity like landing may help elucidate the midfoot's contribution to foot energetics and function. The main purpose of this study was to measure midtarsal joint kinematics and kinetics during a barefoot single-leg landing task. A secondary aim of this study was to explore the relationship between static foot posture and dynamic midfoot function. METHODS: In a cross-sectional study design, 48 females (age = 20.4 ± 1.8 yr, body mass index = 21.6 ± 1.7 kg·m) performed drop landings from a height of 0.4 m onto split force platforms. Subjects hung from wooden rings and landed on their dominant leg. Midtarsal joint kinematic and kinetic data were recorded using a 14-camera optical motion capture system in conjunction with two in-ground force platforms and a custom kinetic three-segment foot model. Foot structure was measuring using the arch height index (AHI) and the static midtarsal joint angle from motion capture. RESULTS: Kinematic data revealed an average sagittal plane midtarsal joint range of motion of 27° through the landing phase. Kinetic data showed that between 7% and 22% of the total lower extremity joint, work during the landing was performed by the midtarsal joint. Both standing AHI and static midtarsal joint angle (static MA) were correlated with sagittal plane midtarsal joint range of motion (standing AHI: r = -0.320, P = 0.026; static MA: r = 0.483, P < 0.001) and with midtarsal joint work (standing AHI: r = 0.332, P = 0.021; static MA: r = -0.323, P = 0.025). CONCLUSION: The midfoot contributes substantially to landing mechanics during a barefoot single-leg landing task. Static foot posture measures have limited value in predicting midfoot kinematics and kinetics during sportlike landings.

Walking in Minimalist Shoes Is Effective for Strengthening Foot Muscles.

INTRODUCTION: Weakness of foot muscles may contribute to a variety of loading-related injuries. Supportive footwear may contribute to intrinsic foot muscle weakness by reducing the muscles' role in locomotion (e.g., absorbing forces and controlling motion). Increased stimulus to the foot muscles can be provided through a variety of mechanisms, including minimalist footwear and directed exercise. PURPOSE: To determine the effect of walking in minimalist footwear or performing foot strengthening exercises on foot muscle size and strength. METHODS: Fifty-seven runners were randomly assigned to one of three groups-minimalist shoe walking (MSW), foot strengthening (FS) exercise, or control (C). All groups maintained their prestudy running mileage throughout the study. The MSW group walked in provided footwear, increasing weekly the number of steps per day taken in the shoes. The FS group performed a set of progressive resistance exercises at least 5 d·wk. Foot muscle strength (via custom dynamometers) and size (via ultrasound) were measured at the beginning (week 0), middle (week 4), and end (week 8) of the study. Mixed model ANOVA were run to determine if the interventions had differing effects on the groups. RESULTS: There were significant group-time interactions for all muscle size and strength measurements. All muscle sizes and strength increased significantly from weeks 0 to 8 in the FS and MSW groups, whereas there were no changes in the C group. Some muscles increased in size by week 4 in the FS and MSW groups. CONCLUSIONS: Minimalist shoe walking is as effective as foot strengthening exercises in increasing foot muscle size and strength. The convenience of changing footwear rather than performing specific exercises may result in greater compliance.

Reliability of doming and toe flexion testing to quantify foot muscle strength.

BACKGROUND: Quantifying the strength of the intrinsic foot muscles has been a challenge for clinicians and researchers. The reliable measurement of this strength is important in order to assess weakness, which may contribute to a variety of functional issues in the foot and lower leg, including plantar fasciitis and hallux valgus. This study reports 3 novel methods for measuring foot strength - doming (previously unmeasured), hallux flexion, and flexion of the lesser toes. METHODS: Twenty-one healthy volunteers performed the strength tests during two testing sessions which occurred one to five days apart. Each participant performed each series of strength tests (doming, hallux flexion, and lesser toe flexion) four times during the first testing session (twice with each of two raters) and two times during the second testing session (once with each rater). Intra-class correlation coefficients were calculated to test for reliability for the following comparisons: between raters during the same testing session on the same day (inter-rater, intra-day, intra-session), between raters on different days (inter-rater, inter-day, inter-session), between days for the same rater (intra-rater, inter-day, inter-session), and between sessions on the same day by the same rater (intra-rater, intra-day, inter-session). RESULTS: ICCs showed good to excellent reliability for all tests between days, raters, and sessions. Average doming strength was 99.96 ± 47.04 N. Average hallux flexion strength was 65.66 ± 24.5 N. Average lateral toe flexion was 50.96 ± 22.54 N. CONCLUSIONS: These simple tests using relatively low cost equipment can be used for research or clinical purposes. If repeated testing will be conducted on the same participant, it is suggested that the same researcher or clinician perform the testing each time for optimal reliability.