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Effect of increased mechanical stimuli on foot muscles functional capacity

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Abstract

INTRODUCTION As biological structures receive mechanical stimuli they are getting stronger. If muscles, tendons and bones are not in use they will decrease strength and their functional capacity. The biological structures of the foot can be trained by barefoot walking or workout through the speculated higher loading. No scientific evidence for a causal relationship between in-creased foot loading and functional improvement of foot structures could be found in the literature. The foot arch and the foot functional capacity is strongly related to the strength of the flexor muscles of the metatarsophalangeal joints (MPJ): M. flexor hallucis longus (FHL) and M. flexor digitorum longus (FDL) [1,2,3]. It was shown that a special designed minimal shoe (Nike FREE) increases the range of motion on the metatarsophalangeal joints (MPJ) and the ankle joint in normal walking and modifies the plantar pressure distribution in a way close to barefoot walking on grass. In a pilot study using wire EMG technique the muscle activity of the FHL was shown to be significantly increased during walking in the minimal footwear in comparison to walking in traditional running shoes. If training with the minimal footwear mimics barefoot training one can assume that using the minimal shoe will increase the loading of the foot structures and make them stronger. The purpose of the study was to demonstrate the capacity of biological structures to adapt to mechanical stimuli modified through footwear and to quantify effects on strength and morphology of the foot and shank muscles. The research question was to quantify the impact of increased mechanical stimuli on (1) muscle strength and (2) anatomical cross sec-tional area (ACSA) of intrinsic foot and shank muscles. METHODS The research question was solved by a prospective longitudinal designed approach. The prospective study operated with an experimental (n E =25) and a control group (n C =25) both consisting of male and female subjects. The experimental intervention over a period of five months was the use of the minimal footwear in athletes preparatory (warm up) training while the control group used traditional training shoes for the same training programme. The measurement of muscle strength was performed by special custom build dynamo-meters. ACSA of FHL, FDL, M. triceps surae (TS), Mm. tib. post (TP) and ant.(TA), M. peroneus (PER) at the greatest circumference of the shank and ACSA of four of the intrinsic foot muscles (M. abductor hallucis, M. quadratus plantae, M. abductor digiti minimi, M. flexor digitorum brevis) were estimated by MRI (Siemens Symphony, 1.5 Tesla). RESULTS AND DISCUSSION The muscle strength changes through the intervention showed a significant (p<.01) increase of the MPJ flexors in the experi-mental group; no significant change in the controls.
EFFECT OF INCREASED MECHANICAL STIMULI ON FOOT MUSCLES FUNCTIONAL CAPACITY
Gert-Peter Brüggemann, Wolfgang Potthast, Björn Braunstein and Anja Niehoff
Institute for Biomechanics and Orthopaedics,
German Sport University Cologne; email: brueggemann@dshs-koeln.de
INTRODUCTION
As biological structures receive mechanical stimuli they are
getting stronger. If muscles, tendons and bones are not in use
they will decrease strength and their functional capacity. The
biological structures of the foot can be trained by barefoot
walking or workout through the speculated higher loading.
No scientific evidence for a causal relationship between in-
creased foot loading and functional improvement of foot
structures could be found in the literature. The foot arch and
the foot functional capacity is strongly related to the strength
of the flexor muscles of the metatarsophalangeal joints
(MPJ): M. flexor hallucis longus (FHL) and M. flexor
digitorum longus (FDL) [1,2,3]. It was shown that a special
designed minimal shoe (Nike FREE) increases the range of
motion on the metatarsophalangeal joints (MPJ) and the ankle
joint in normal walking and modifies the plantar pressure
distribution in a way close to barefoot walking on grass. In a
pilot study using wire EMG technique the muscle activity of
the FHL was shown to be significantly increased during
walking in the minimal footwear in comparison to walking in
traditional running shoes. If training with the minimal
footwear mimics barefoot training one can assume that using
the minimal shoe will increase the loading of the foot
structures and make them stronger.
The purpose of the study was to demonstrate the capacity of
biological structures to adapt to mechanical stimuli modified
through footwear and to quantify effects on strength and
morphology of the foot and shank muscles. The research
question was to quantify the impact of increased mechanical
stimuli on (1) muscle strength and (2) anatomical cross sec-
tional area (ACSA) of intrinsic foot and shank muscles.
METHODS
The research question was solved by a prospective
longitudinal designed approach. The prospective study
operated with an experimental (nE=25) and a control group
(nC=25) both consisting of male and female subjects. The
experimental intervention over a period of five months was the
use of the minimal footwear in athletes preparatory (warm up)
training while the control group used traditional training shoes
for the same training programme. The measurement of muscle
strength was performed by special custom build dynamo-
meters. ACSA of FHL, FDL, M. triceps surae (TS), Mm. tib.
post (TP) and ant.(TA), M. peroneus (PER) at the greatest
circumference of the shank and ACSA of four of the intrinsic
foot muscles (M. abductor hallucis, M. quadratus plantae, M.
abductor digiti minimi, M. flexor digitorum brevis) were
estimated by MRI (Siemens Symphony, 1.5 Tesla).
RESULTS AND DISCUSSION
The muscle strength changes through the intervention showed
a significant (p<.01) increase of the MPJ flexors in the experi-
mental group; no significant change in the controls.
VK LK DK TP FHL FDL
0
1
2
3
4
5
'Volumen [%]
TA PER TS TP FHL FDL
ǻACSA [%]
VK LK DK TP FHL FDL
0
1
2
3
4
5
'Volumen [%]
TA PER TS TP FHL FDL
ǻACSA [%]
Figure 1: Relative increase of ACSA of six extrinsic foot
muscle through the five months intervention (Mean and
SEM); experimental group (nE=25).
Table 1: Changes in MPJ flexor strength [N], subtalar
inversion strength [Nm], plantar and dorsi flexors strengths
[N]. Means and SEM. *: p<.05, **:p<.01.
Experimental group Control group
Pre Post Pre Post
MPJ flexor strength 232 (10.9) 279 (11.6) ** 228 (11.1) 237 (11.6) ns
Inversion moment 18.0 (1.4) 21.8 (1.6) * 17.5 (1.3) 17.7(1.2) ns
Plantar fl. strength 1065(72.2) 1254(73.2) * 1296(68.0) 1242(63.1) ns
Dorsi fl. strength 432(18.0) 460(18.9) * 415(20.6) 419 (14.8) ns
Plantar flexion strength increased only significantly (p<.05)
in the experimental group. The maximum supinator muscles
torque increased for the experimental group (p<.05) and
showed no effect on the control group. While for the Mm
tibialis anterior, peronei, tibialis posterior and triceps surae no
significant changes in the ACSA were found, the ACSA of
the Mm flexor hallucis and flexor digitorum increased by
approximately 4% and by 5% for the Mm abductor hallucis
and quadratus plantae in the experimental group.
CONCLUSIONS
The use of minimal footwear was related to changes in muscle
strength and morphology. It was demonstrated that the
footwear increased mechanical stimuli on the tendon muscle
units. The muscle strength capacity of those muscles which
were more intensively used by the minimal shoe increased
significantly. Muscles which were similar activated in both
conditions did not respond. One can conclude that footwear
technology impacts the mechanical loading as well as the
biological response of the loaded tissues.
REFERENCES
1. Jacob, HAC. Clin Biomech 6, 783-792, 2001,
2. Kitaoka, HB et al. Foot Ankle Int 15(10), 557-560, 1994.
3. Tochigi,Y. Foot Ankle Int 24(8), 634-639,2003.
ACKNOWLEDGEMENTS
This study has been financially supported by Nike.
553
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