Background
Shoe weight can be used to categorise running shoes. Shoes with a weight of 150–200 g are called light shoes, shoes with a weight of 200–300 g are called minimalist shoes and shoes with a weight of 360 g or greater are called heavy shoes [
1]. Minimalist shoes have been speculated to strengthen foot muscles and arches, which may help prevent injuries [
2]. The reasons for this phenomenon may be that impact force on the ground acts as an input signal to trigger muscle tuning [
3], and runners use their own comfort mechanisms to maintain their preferred movement path and reduce the risk of injury [
4].
Previous studies have noted that reducing the weight of shoes has been found to improve running economy [
5]. Previous studies have also observed that adding 100 g of weight per shoe increases the submaximal VO2 (increases oxygen consumption) by ~ 1% [
6]. Hoogkamer et al. also found that adding 100 g of mass per shoe increases metabolic rate by 0.75% at a velocity of 3.5 m·s-1 during the 3000 m time-trial running [
7]. This concept of compensation for additional shoe weight implies decreased movement efficiency when performing in heavy shoes [
8]. Runners with heavy shoes produce more oxygen and consume more energy than those with lightweight shoes, resulting in a low running efficiency [
9]. Reducing the weight of shoes increases the efficiency of running because less force must be generated by muscles, and less mechanical work is required. When muscles perform mechanical work, they consume energy. Therefore, shoes of different weights and configurations can change a runner’s foot muscles and energy consumption.
The lack of arch support in minimalist running shoes have been shown to increase the strength of foot muscles [
10]. This concept is reflected by an increase in the cross-sectional areas of both intrinsic and extrinsic foot muscles after a period of running in minimalist shoes that mimic barefoot running [
11]. Further, use of Vibram FiveFinger minimalist shoes have been shown to increase the intrinsic muscle thickness and strength of the abductor hallucis muscle [
12]. These effects have been proposed to reduce the risk of muscle injury.
Different shoes (i.e. different shoe masses) may change a runners foot strike patterns [
13], which in turn may affect muscle activation in the lower extremities. Musculoskeletal models may be used as generic models or subject-specific models. The generic models made by generic data measurements from cadaveric quantity information [
14,
15]. To date, these effects have not been reported during running with shoes of different weights focus on calf individual muscle contributions.
Therefore, the aim of the current investigation was to examine forces produced by muscles and contributions of calf muscles during the braking phase. The hypotheses were that a large shoe mass would result in increased calf muscle activation during the braking phase of a running cycle. This study may provide important information regarding the extent of the recruitment of key muscles when running with shoes of different weights.
Results
The results showed that the contribution rate of the lateral gastrocnemius muscle during the braking phase was 5.7% in 175 g shoes, 4.0% in 255 g and 335 g shoes, and 3.1% in 415 g shoes (Table
1). The results indicated that the lateral gastrocnemius contribution of the calf muscle was significantly different during the braking phase.
Table 1
Individual calf muscle contributions during the braking phase
Tibialis anterior | 6.5 ± 0.029 | 7.2 ± 0.031 | 7 ± 0.033 | 6.9 ± 0.029 | 0.930 |
Extensor hallucis longus | 6.7 ± 0.031 | 6.9 ± 0.033 | 6.2 ± 0.034 | 7 ± 0.029 | 0.851 |
Extensor digitorum longus 1st | 5.2 ± 0.028 | 4.6 ± 0.028 | 6.3 ± 0.024 | 4.5 ± 0.016 | 0.195 |
Extensor digitorum longus 2nd | 6.8 ± 0.028 | 7.2 ± 0.022 | 7 ± 0.029 | 5.1 ± 0.023 | 0.151 |
Extensor digitorum longus 3rd | 6.8 ± 0.030 | 7.2 ± 0.026 | 7.2 ± 0.029 | 6.1 ± 0.026 | 0.684 |
Fibularis peroneus brevis | 7.4 ± 0.023 | 6.5 ± 0.026 | 6.9 ± 0.024 | 6.5 ± 0.038 | 0.794 |
Gastrocnemius lateralis | 5.7 ± 0.029 | 4 ± 0.020 | 4 ± 0.022 | 3.1 ± 0.020 | 0.043* |
Gastrocnemius medialis | 4.6 ± 0.023 | 3.7 ± 0.027 | 3.9 ± 0.016 | 3.9 ± 0.016 | 0.717 |
Soleus | 7.8 ± 0.030 | 6.5 ± 0.034 | 5.3 ± 0.035 | 8.1 ± 0.031 | 0.132 |
Flexor hallucis longus | 6.4 ± 0.022 | 4.9 ± 0.033 | 6.8 ± 0.036 | 6.3 ± 0.028 | 0.361 |
Flexor digitorum longus 1st | 6.3 ± 0.044 | 7.4 ± 0.039 | 6.2 ± 0.021 | 7.1 ± 0.026 | 0.792 |
Flexor digitorum longus 2nd | 5.1 ± 0.020 | 4.2 ± 0.023 | 5.2 ± 0.025 | 4.9 ± 0.015 | 0.516 |
Flexor digitorum longus 3rd | 6.3 ± 0.044 | 7.4 ± 0.039 | 6.2 ± 0.021 | 7.1 ± 0.026 | 0.792 |
Tibialis posterior 1st | 4.9 ± 0.014 | 5.5 ± 0.021 | 5.7 ± 0.022 | 6.5 ± 0.014 | 0.194 |
Tibialis posterior 2nd | 4.7 ± 0.009 | 5.9 ± 0.022 | 5.3 ± 0.022 | 5.6 ± 0.016 | 0.474 |
Tibialis posterior 3rd | 4.7 ± 0.008 | 5.6 ± 0.019 | 5.6 ± 0.018 | 5.6 ± 0.015 | 0.518 |
Tibialis posterior 4th | 4.1 ± 0.016 | 5.3 ± 0.026 | 5.2 ± 0.018 | 5.3 ± 0.017 | 0.445 |
The lateral gastrocnemius muscle contributions results showed significant differences between the shoe weight groups (p = 0.043). The post hoc comparisons revealed that the lateral force contributions of the gastrocnemius muscle during the braking phase was larger in the 175 g shoe condition than in the 415 g shoe condition (p = 0.023). There were no other significant differences in other muscle contributions throughout the gait cycle.
Discussion
This study assessed the differences in the forces produced by skeletal muscles and activation patterns of calf muscles during the braking phase while participants ran wearing shoes of different weights. A previous study showed that compared to running while wearing shoes, running barefoot results in higher activation of the gastrocnemius muscle [
22]. Similarly, another study found that in the time of peak activity of the lateral gastrocnemius, running with heavy shoes significantly delayed the gait cycle by approximately 4% [
23]. However, J Becker, BJJoE Borgia and Kinesiology [
24] found no difference in lateral gastrocnemius muscle activation during the whole gait cycle. In this study, differences were found in the braking phase, which may indicate that different shoe weights can change muscle activation during the braking phase. The inter-joint coordination risk of running injuries usually occurs in the braking phase [
16]. The increasing muscle activity leads to an increasing load on that muscle [
22], and an increasing load might cause injury to the Achilles tendon, which is highly vulnerable to repetitive overload during running activities [
25,
26]. Therefore, wearing a light shoe that results in the excessive activation of the gastrocnemius lateralis during the braking phase may increase the incidence of muscle injuries.
Minimalist running shoes can influence the role each muscle has in controlling the motion of the body, with a trend towards higher muscle forces in the gastrocnemius and soleus muscles and higher energy transfers [
27]. An appropriate shoe affects the landing impact force when running, which can trigger muscle tuning [
3] to allow the skeleton to move in its preferred path through self-determined comfort mechanisms [
4]. Minimalist shoes are lighter than traditional shoes, so when people run in minimalist shoes, the gastrocnemius lateralis activates more during the braking phase. The lightest shoes are designed to mimic barefoot conditions. A previous study compared muscle simulations of running in shoes and running barefoot and found that the peak muscle forces of the vastus medialis, vastus lateralis, rectus femoris, and tibialis anterior were larger in the barefoot condition. When barefoot running was simulated, the gastrocnemius had a large peak muscle force [
13]. In this study, shoes with the same structure and different weights were compared, and the gastrocnemius lateralis was found to have the largest muscle contributions. Therefore, a light shoe may also cause fatigue in the gastrocnemius lateralis.
Minimalist and lightweight shoes are associated with decreased knee extensor individual muscle contributions and increased ankle joint angles [
28]. These factors increase the load on the ankle joint and increase the contribution of the triceps surae muscles [
28]. The 175 g shoes may cause greater activation of the gastrocnemius lateralis. A previous study showed that running extreme distances requires more training of the gastrocnemius muscles to prevent muscle fatigue and reduce the risk of injury [
29]. The results of this study show that the lightest shoes resulted in the largest muscle contributions, so wearing lightweight shoes likely results in more gastrocnemius fatigue compared to wearing heavy shoes. Participants showed more FFS when wearing the 175 g shoes than when wearing the 415 g shoes [
30]. Medial and lateral gastrocnemius activity increases during FFS running, and these heightened activity levels may lead injury because of the overuse of the medial and lateral gastrocnemius muscle [
31]. Therefore, wearing lightweight shoes without training may increase the likelihood of injury. This is consistent with previous research which found that transitioning form a RFS to a non-rearfoot strike will reduce running economy and increase loads at the ankle and ankle plantarflexors [
32]. Therefore, as wearing lightweight shoes may change a runners strike pattern, it may also increase the risk of injury at these sites. Immediate changes lightweight shoes may cause muscle damage due to the excessive fatigue of the ankle joint muscles during the initial wear period. There are limitations to this study, including the use of simulated muscle models rather than EMG data. Furthermore, an attempt was made to blind the participants, as stated in the methods; however, the runners were clearly not blinded to the weights of the shoes since they could see the weights attached. This factor could have introduced performance bias.
Conclusion
This study explored the differences between running shoes with the same structure but different weights. The contribution of the gastrocnemius lateralis, i.e., the integral of the force generated, increased for lightweight shoes. Therefore, wearing lightweight shoes may promote muscle fatigue in the gastrocnemius during the braking phase. Calf muscle activation may be indicative that an adaptation period is warranted when changing from heavy to lightweight shoes.
Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit
http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (
http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.