Alterations in Running Biomechanics after 12 Week Gait Retraining with Minimalist Shoes

Purpose: The intervention of 12 week gait retraining with minimalist shoes was established to examine its e ect on impact forces, joint mechanics, and vertical sti ness during running.Methods: Thirty male recreational runners were randomly assigned to the gait retraining+minimalist shoe (n=15, GR) and minimalist shoe (n=15, MIN) groups. The ground reaction force and marker trajectories were collected before and after intervention at a speed of 3.33 5% m/s.Results: A total of 17 participants (9 in the GR group and 8 in the MIN group) completed the training. After training, (1) the loading rate of both groups decreased signi cantly, and the loading rate of the GR group was lower than that of the MIN group. (2) The foot strike angle of the GR group decreased signi cantly after training, and the plantar exion angle and hip joint angular extension velocity increased in both groups. (3) The moment of ankle joint increased in the GR group, and the sti ness of lower limbs was signi cantly improved in both groups.Conclusion: The 12 week gait retraining with minimalist shoes converted rearfoot strikers into forefoot strikers with a rate of 78% (7/9). More importantly, such a combined program, compared to the training with only minimalist shoes, can avoid the peak impact force and decrease the loading rate more e ectively, thus providing a potential means of reducing risk of running injury caused by impact forces. Moreover, the increased vertical sti ness of lower extremity after gait retraining

a rate of 78% (7/9). More importantly, such a combined program, compared to the training with only minimalist shoes, can avoid the peak impact force and decrease the loading rate more e ectively, thus providing a potential means of reducing risk of running injury caused by impact forces. Moreover, the increased vertical sti ness of lower extremity after gait retraining may improve running economy and corresponding energy utilization. However, these observations also suggest that the sole use of minimalist footwear may have limited e ects on reducing running-related impacts. Keywords:gait retraining; running biomechanics; strike pattern; minimalist shoe 1. Introduction As one of the most popular sports in the world, running is attracting increasing attention nowadays [1]. However, a high injury rate (19–79%) in running has been reported [2]. The impact load is two to three times of the body weight at touchdown, which is considered to be the main risk factor for causing damage such as stress fracture/fracture, patellofemoral joint pain syndrome, and plantar fasciitis [2–5]. Thus, how to reduce the impact and risk of running injury has always been a hot issue in the biomechanics, sports medicine, rehabilitation, and related industries [6,7]. In the past 50 years, the injury rate of running has not changed much despite the development of running shoes [8]. Studies show that the cushioning function of running shoes cannot be utilized in actively landing [6,9,10]. Hence, researchers have considered di erent shoe designs and the postural control in lower limbs whilst running. As a result, gait retraining and minimalist shoe training derived Int. J. Environ. Res. Public Health2020,17, 818; doi:10.3390 /ijerph17030818 /journal/ijerph

Int. J. Environ. Res. Public Health2020,17, 818 2 of 13 from barefoot running theory have been applied to rehabilitation, medical treatment, and sports elds [11–14]. Minimalist footwear are shoes with a lighter mass, greater exibility, and lower heel-to-toe drop than conventional running shoes [15]. Runners who use this type of footwear likely adopt a non-rearfoot strike pattern [16,17], which can reduce impact forces [11,16]. McCarthy et al. [13] showed that after a 12 week simulated barefoot training, in which the participants were free to adopt their own running pattern, 100% used non-rearfoot strike patterns. Latorre-Roman et al. [18] found that a 12 week barefoot training program causes signi cant changes in the foot strike pattern, with a tendency towards midfoot or forefoot strikes. However, not all runners who are used to wearing conventional shoes can switch to non-rearfoot strike when wearing minimalist shoes [18]. Without the cushioning of conventional shoes, the risk of high impact-related injuries likely increases [19,20]. Therefore, combining gait retraining and minimalist shoes may be more e ective and secure than adopting the two separately. Gait retraining, an active training program with instruction or feedback, di ers from the minimalist shoe training, which is a passive adaptive process of special shoe conditions (e.g., minimalist shoes, barefoot shoes). Promoting a forefoot strike pattern, which is similar to the barefoot movement in the literature, is considered as a possible way forward [17,21]. In addition to promoting non-rearfoot strike patterns, gait retraining encourages forefoot/midfoot strike for a high frequency, light stride and an upright posture [21,22]. Gait retraining reduces loading rate and impact peak by increasing the stride frequency and adopting a non-rearfoot strike pattern [16,21,23]. Warne et al. [12] showed that a 6 week combination program of gait retraining with minimalist shoes causes more signi cant changes than that of gait retraining with conventional shoes. In light of the above information, the combination of gait retraining and minimalist shoes can reduce the loading rate and peak impact force by using a non-rearfoot strike pattern [13,16,23]. The implication is that the shoe condition should match the running posture. However, the

with minimalist shoes causes more signi cant changes than that of gait retraining with conventional shoes. In light of the above information, the combination of gait retraining and minimalist shoes can reduce the loading rate and peak impact force by using a non-rearfoot strike pattern [13,16,23]. The implication is that the shoe condition should match the running posture. However, the long-term impact on the running posture of such a combination program remains unclear. The combined training program with a long incremental load may be e ective and safe. The purpose of this study was to establish a combined intervention mode of 12 week gait retraining with minimalist shoes and examine its e ect on factors related to the risks of running injury and performance, i.e., impact forces, joint mechanics, and vertical sti ness. The hypothesis was that the participants received 12 week gait retraining with minimalist shoes would have a lower loading rate and a decreased foot-strike angle compared to that of those who only used minimalist shoes. 2. Methods 2.1. Participants Thirty recreational male runners (age: 30.0 6.4 years; height: 175.0 5.2 cm; body mass: 71.9 9.4 kg; weekly running volume: 27.4 8.7 km) were recruited. Inclusion criteria are as follows: (1) they ran at least 3 days per week with a minimum of 20 km/week for at least 3 months prior to the study and (2) they were used to running with rearfoot strike in cushioned shoes and had no experience of barefoot running or special sneakers (e.g., ve- nger shoes, minimalist shoes, and racing spikes). Prior to this experiment, participants completed a basic information questionnaire and signed an informed consent form to ensure that they had no musculoskeletal injuries for the past 6 months. This study was approved by the Institutional Review Board of the Shanghai University of Sport (no. 2017007). 2.2. Experimental Design A parallel randomized control design was used in this study. Thirty participants were randomly (random number sort) divided into gait retraining+minimalist shoe (GR) and minimalist shoe (MIN) groups. The two groups underwent the same testing process but with di erent interventions (Figure).

approved by the Institutional Review Board of the Shanghai University of Sport (no. 2017007). 2.2. Experimental Design A parallel randomized control design was used in this study. Thirty participants were randomly (random number sort) divided into gait retraining+minimalist shoe (GR) and minimalist shoe (MIN) groups. The two groups underwent the same testing process but with di erent interventions (Figure).

Int. J. Environ. Res. Public Health2020,17, 818 3 of 13 Foot size was measured, and participants in both groups were provided with a pair of minimalist footwear (type INOV-8 Bare-XF 210 V2: 3 mm outsole, no midsole, 0 mm heel-toe drop, 227 g weight). Figure 1.Flow diagram of this study. 2.3. Testing Procedure A 10-camera motion capture system (100 Hz, T40, Vicon Motion Inc., Oxford, United Kingdom) was used to collect kinematic data including hip, knee, and ankle joints (Figure). Two 90 60 10 cm Kistler 3D force platforms (9287B, Kistler Corporation, Winterthur, Switzerland) were used to collect ground reaction force (GRF) data at a sampling rate of 1000 Hz. Before the over-ground test, the participants performed a 5 min warm-up on a treadmill at optional running speed with the minimalist shoes, followed by 1 min 3.33 m/s experimental speed adaptation. During the over-ground test, three successful right foot contacts on the force plate were required. Its presence was not mentioned to avoid targeting problems. The speed during the over ground test was monitored to ensure the participants ran at 3.33 m/s using a Witty-Manual grating timing system (Witty wireless training timer, Microgate Corp., Bolzano, Italy) with a 5% acceptable variance. Both the GR and the MIN groups were tested before and after the intervention.

Int. J. Environ. Res. Public Health2020,17, 818 4 of 13 Figure 2.The marker-set and the experimental setup. 2.4. Intervention GR group: The participants were required to run at a medium-intensity self-selected speed with minimalist shoes and strike with forefoot. A pressure sensitive insole (Podoon) was applied to GR runners to distinguish foot strike patterns. The sensors were located at the metatarsophalangeal joint and heel. Sound feedback could be obtained from a mobile application if participants struck with the heel. The gait retraining program lasted 12 weeks and was three times a week. The duration of the training gradually increased from 5 min in the 1st week to 48 min in the 12th week (Table) [ 12,13]. Weekly group training was also provided to ensure the quality of retraining and to minimize the dropout rates. After each training, the experimenter will remind the participants who do not meet the requirements or mismatch with the data in the cloud. Table 1.The 12 week gait retraining intervention. Week 1 2 3 4 5 6 7 8 9 10 11 12 Duration (min) 5 10 15 20 25 30 35 40 42 44 46 48 Times per week 3 3 3 3 3 3 3 3 3 3 3 3 MIN group: During the running training, the participants were required to run at a medium- intensity self-selected speed wearing minimalist shoes without any instructions for the strike pattern. A pressure-sensitive insole (Podoon) was also applied to MIN runners for matching the same insole condition of the GR group, but they did not receive the mobile application that provided sound feedback. The schedule was the same as that of the GR group. The intervention training was only an alternative part of the training [12,13]. The total running distance per week was unchanged. Participants kept record training logs, including the time training start/stop, location, and distance. During training, they were told that any discomfort or injury needed to be reported to the experimenter. The researchers checked the training logs stored in the cloud.

total running distance per week was unchanged. Participants kept record training logs, including the time training start/stop, location, and distance. During training, they were told that any discomfort or injury needed to be reported to the experimenter. The researchers checked the training logs stored in the cloud.

Int. J. Environ. Res. Public Health2020,17, 818 5 of 13 The participants in both groups were allowed to wear habitual running shoes when out of training. During training sessions, the two groups were prevented from interacting with one another. Inclusion criteria: (1) completed all tests, (2) no more than three absences, and (3) completed the last 3 weeks' training with no more than six absences. Those who satis ed any condition were included. During training, participants were allowed to delay or withdraw due to injury or personal reasons. 2.5. Data Processing Kinematic data and GRF were analyzed via the gait analysis software Visual 3D (v5, C-Motion, Inc., Germantown, MD, USA) using inverse dynamics. The GRF was ltered with a cut-o frequency of 100 Hz. Marker trajectories were ltered with a cut-o frequency of 7 Hz [10] via a fourth-order Butterworth low-pass lter. The hip, knee, and ankle angles of the lower limb were de ned on the basis of our previous model [24], and the kinematic features of each joint were calculated. Impact variables included peak impact forces and maximum loading rates. The maximum loading rate (LR) is equivalent to a slope of 20–80% of rst peak (FP). If FP is non-existent, then LR is calculated by using 13% of the gait cycle as a representative value [25,26]. Kinematic variables included (1) ground contact time (CT), which represents the duration between touchdown to o -ground; (2) strike angle ( f) which refers to the angle between the foot and ground at initial contact; (3) angles of the hip, knee, and ankle joints when contacting the ground ( 0) and the maximum joint angle ( max); and (4) joint angular velocities including the angular velocity at initial contact (!0) and the maximum angular velocity of hip, knee, and ankle joints (!p). The angle of ankle joint was 0 during standing, negative for extension/plantar exion, and positive for exion/dorsi exion (Figure). Kinetic variables included (1) joint moment determined by the net moment generated by the muscles of the hips, knees, and ankles of the lower limbs using the inverse dynamics in Visual

maximum angular velocity of hip, knee, and ankle joints (!p). The angle of ankle joint was 0 during standing, negative for extension/plantar exion, and positive for exion/dorsi exion (Figure). Kinetic variables included (1) joint moment determined by the net moment generated by the muscles of the hips, knees, and ankles of the lower limbs using the inverse dynamics in Visual 3D biomechanical analysis software; (2) peak extension joint power (p), which is the product of the net moment (M) and joint angular velocities (!), and (3) vertical sti ness (k=GRFi/Dy) [27]. For the joint moment, the maximum extension moment (Mmax) of each joint was selected. GRFirepresents the vertical GRF when the center of gravity (CoG) was lowest, andDyrepresents the vertical displacement of CoG during centrifugation. Figure 3.Angles of lower extremity joints.

Int. J. Environ. Res. Public Health2020,17, 818 6 of 13 2.6. Statistics The mean and standard deviation for each variable were calculated. The results of each group of pre/post were tested for normality. The original value was used in all tables and gures for comparison. A two-way repeated measure ANOVA was used to examine the e ects of retraining (pre- and post-training) and groups (GR and MIN) on each variable (Version 22.0; SPSS, Inc., Chicago, IL, USA). Independentt-tests and pairedt-tests were used as post-hoc tests when a signi cant interaction was detected. The signi cance level was set as =0.05. 3. Results 3.1. Dropout Rate Seventeen participants completed intervention and met the inclusion criteria (nine in the GR group, eight in the MIN group) (Table). Speci cally, an FFS runner in the GR group was excluded after pre-test. During intervention, two participants (one in GR, one in MIN) were excluded due to injuries caused by non-training related events, i.e., walked downstairs carelessly. Two participants (one in GR, one in MIN) were excluded due to mismatch of the cloud data, and they could not provide reliable evidence, such as app or smart watch data. Three participants (one in GR, two in MIN) who lost contact during the training were excluded. Five participants (two in GR, three in MIN) who quit or missed too much training were also excluded. No signi cant di erence was observed in the average running volumes between the GR and MIN groups (GR: 28.3 11.2 km/week, MIN: 26.9 10.7 km/week). Table 2. Information of the participants who completed training. GR: gait retraining+minimalist shoe, MIN: minimalist shoe. Age (years) Height (cm) Body Mass (kg) km per Week (km) GR (n=9) 32.4 6.1 174.8 5.3 70.2 6.0 28.3 11.2 MIN (n=8) 27.6 5.2 173.9 7.0 75.4 11.7 26.9 10.7 t-test p=0.104 p=0.773 p=0.262 p=0.787 3.2. Impact Forces A signi cantly main e ect of time on the loading rate was observed (Figure; Table), which was signi cantly reduced by 22.6% (GR) and 17.2% (MIN) after training (p<0.001,p=0.017). The loading rate of the GR group was lower than that of

MIN (n=8) 27.6 5.2 173.9 7.0 75.4 11.7 26.9 10.7 t-test p=0.104 p=0.773 p=0.262 p=0.787 3.2. Impact Forces A signi cantly main e ect of time on the loading rate was observed (Figure; Table), which was signi cantly reduced by 22.6% (GR) and 17.2% (MIN) after training (p<0.001,p=0.017). The loading rate of the GR group was lower than that of the MIN group after training (p=0.015). No interaction e ect was noted between time group for any other GRF parameters in this study. Figure 4.Comparison of loading rate between two groups before and after training.

This study investigates the effects of gait retraining with minimalist shoes on running biomechanics.