Associations between the size of individual plantar intrinsic and extrinsic foot muscles and toe flexor strength

Abstract

Background The size of the plantar intrinsic and extrinsic foot muscles has been shown to be associated with toe flexor strength (TFS). Previous studies adopted the size of limited plantar intrinsic foot muscles or a compartment containing several muscles as an independent variable for TFS. Among the plantar intrinsic and extrinsic foot muscles, therefore, it is unclear which muscle(s) primarily contributes to TFS production. The present study aimed to clarify this subject. Methods In 17 young adult men, a series of anatomical cross-sectional area of individual plantar intrinsic and extrinsic foot muscles was obtained along the foot length and the lower leg length, respectively, using magnetic resonance imaging. Maximal anatomical cross-sectional area (ACSAmax) and muscle volume (MV) for each constituent muscle of the plantar intrinsic foot muscles (flexor hallucis brevis; flexor digitorum brevis, FDB; abductor hallucis; adductor hallucis oblique head, ADDH-OH; adductor hallucis transverse head, ADDH-TH; abductor digiti minimi; quadratus plantae) and extrinsic foot muscles (flexor hallucis longus; flexor digitorum longus) were measured. TFS was measured with a toe grip dynamometry. Results TFS was significantly associated with the ACSAmax for each of the ADDH-OH (r = 0.674, p = 0.003), ADDH-TH (r = 0.523, p = 0.031), and FDB (r = 0.492, p = 0.045), and the MV of the ADDH-OH (r = 0.582, p = 0.014). As for the ADDH-OH, the correlation coefficient with TFS was not statistically different between ACSAmax and MV (p = 0.189). Stepwise multiple linear regression analysis indicated that ACSAmax and MV of the ADDH-OH alone explained 42 and 29%, respectively, of the variance in TFS. Conclusion The ADDH-OH is the primary contributor to TFS production among the plantar intrinsic and extrinsic foot muscles as the result of the stepwise multiple linear regression analysis.

Strength and size relationships of toe flexor muscles with special reference to the toes intended for force production

“…Thus, the current result may be attributable to the fact that the anatomical function of the FHB would be the most suitable for the toe pushing action. In addition, the current results on the relationship between muscle size and TFS-All also differed from those reported by Kusagawa et al 5 , in which the ACSA max of ADDH-OH was selected as the primary contributor to TFS-All production. In contrast to the present study, Kusagawa et al 5 measured the TFS-All using a toe grip dynamometer, which requires toe gripping action.…”

“…Then, the right foot and ankle were encased in the ankle coils (Foot/Ankle coil, Siemens Healthcare), and the ankle joint was positioned at 90° of plantar exion (neutral position) using a Velcro strap to reduce motion artefacts. In accordance with the previous studies 5,15 , serial longitudinal relaxation time (T1)-weighted MR foot images of the range from the posterior part of the calcaneus to beyond the metatarsophalangeal (MTP) joint were acquired using a fast spin-echo sequence, with the following parameters: repetition time = 700 ms, echo time = 12 ms, average = 3, slice thickness = 3.5 mm, gap between slices = 0 mm, eld of view = 125 × 125 mm, ip angle = 120°, and matrix = 512 × 512. To obtain MR images of the right lower leg, the participants were positioned on the examination table with their lower legs placed parallel to the main magnetic eld.…”

“…Toe exor strength (TFS) is a variable that re ects the force generation capacity of toe exor muscles, comprising the plantar intrinsic foot muscles and extrinsic toe exors 1 . This has been substantiated by studies showing that the size of the plantar intrinsic foot muscles and extrinsic toe exors is signi cantly related to TFS [2][3][4][5][6] . Among the constituents of these muscle groups, some ex the great toe (e.g., exor hallucis brevis [FHB] and exor hallucis longus [FHL]), while others drive lesser toes exion (e.g., exor digitorum brevis [FDB] and exor digitorum longus [FDL]) 7 .…”

“…Of the plantar intrinsic foot muscles, other muscles that could not be visually separated from each other (i.e., lumbricals, exor digiti minimi, and plantar interossei) were excluded from the analysis. The distance between the medial calcaneal tuberosity and the sesamoids bone of the rst metatarsal of MR images was de ned as the foot length (FL) 5,15,16 . The ACSAs of the plantar intrinsic foot muscles at 5% intervals along the FL were calculated by using spreadsheet software (Microsoft Excel, Microsoft Corp., Redmond, WA), and expressed relative to the FL (0% FL: medial calcaneal tuberosity, 100% FL: sesamoids bone of the rst metatarsal).…”

“…Of the previous studies examining the association between TFS and the toe exor muscle size, most investigated the TFS produced by all toes (TFS-All) [3][4][5] , while other studies have attempted to determine the TFS produced by only the great toe (TFS-Great) 2,6 or the lesser toes (TFS-Lesser) 2,3 . These studies reported that the magnitude of TFS production depends on the toe(s) intended for force production.…”