Barefoot Running and Hip Kinematics Good News for the Knee? COLM M CCARTHY1, NEIL FLEMING2, BERNARD DONNE1, and BRIAN BLANKSBY3
Depat tments of Anatomy and Physiology, Trinity College Dublin, IRELAND; ~Department oj Kinesiology, Recreation and Sport, Indiana State University, Terre Haute, IN; and 3School o f Sport Science, Exercise and Health, University o f Western Australia, Crawley, AUSTRALIA
ABSTRACT MCCARTHY, C., N. FLEMING, B. DONNE, and B. BLANKSBY. Barefoot Running and Hip Kinematics: Good News for the Knee?
Med. Sci. Sports Exerc., Vol. 47, No. 5, pp. 1009-1016, 2015. Purpose: Patellofemoral pain and iliotibial band syndromes are common running injuries. Excessive hip adduction (HADD), hip internal rotation (H1R), and contralateral pelvic drop (CLPD) during running have been suggested as causes of injury in female runners. This study compared these kinematic variables during barefoot and shod running. Methods: Three-dimensional gait analyses of 23 habitually shod, uninjured female recreational athletes r unning at 3.33 m -s '1 while shod and barefoot were studied. Spatiotemporal and kinematic data at initial contact (IC), 10% of stance (corresponding to the vertical impact peak), and peak angles were collected from each participant for HADD, HIR, and CLPD, and differences were compared across footwear conditions. Results: Step rates when running barefoot were 178 ± 13 versus 172 ±11 steps per minute when shod (P < 0.001). Foot-strike patterns changed from a group mean heel-toe latency indicating a rear-foot strike (20.8 ms) when shod, to one indicating a forefoot strike (-1 .1 ms) when barefoot (Z3 < 0.001). HADD was lower at IC and at 10% of stance when running barefoot (2.3° ± 3.6° vs 3.9° ± 4.0°, P < 0.001 and 2.8° ± 3.5° vs 3.8° + 3.7°, P < 0.01), as was HIR (7.9° ± 6.1° vs 10.8° ± 6.1°, P < 0.001 and 4.1° + 6.3° vs 7.0° + 5.8°, P < 0.01) and CLPD (0.4° ± 2.4° vs -0 .4 ° ± 2.3°, P < 0.01 and 0.8° + 2.7° vs 0.3° ± 2.5°, P < 0.05). There were no significant differences detected in peak data for hip kinematics. Conclusions: Barefoot running resulted in lower HADD, HIR, and CLPD when compared to being shod at both IC and 10% of stance, where the body’s kinetic energy is absorbed by the lower limb. Because excessive HADD, HIR, and CLPD have been associated with knee injuries in female runners, barefoot running could have potential for injury prevention or treatment in this cohort. Key Words: GAIT, BIOMECHANICS, LOWER LIMB, PATELLOFEMORAL, ILIOTIBIAL BAND, RETRAINING
that PFPS is associated with decreased hip strength, specifi cally of abduction and external rotation. A correlation has also been established between PFPS and faulty hip mechanics during running; namely, excessive hip internal rotation (HIR) and adduction (HADD) (6,22,26,27,35). There is prospective evidence that greater HADD is present among women who go on to develop PFPS (26). Studies have proposed that increasing HADD and HIR results in displacement of the patella laterally relative to the femur, thus decreasing patellofemoral contact area and increasing lateral patellofemoral joint (PFJ) stress and forces on the subchondral bone, leading to pain (28,38). This dynamic valgus movement o f the distal femur and knee has also been suggested to increase strain on the ITB, compressing the richly innervated fat-pad underlying it at the lateral femoral condyle, leading to pain (25). Noehren et al. (25) reported that excessive HADD was one o f the strongest predictors o f developing ITBS in a prospective study of 100 female runners. Ferber et al. (14) also documented that female runners with a history of ITBS exhibited signifi cantly greater HADD than those with no history. Contralateral pelvic drop (CLPD) is when the level of the pelvis o f the nonstance leg drops during running or single leg functional exercises; CLPD increases because of weak hip abductors on the stance side and excessive CLPD has been identified in female runners with PFPS (35).
Address for correspondence: Dr. Colm McCarthy, 9 Boreham Street, Cottesloe, WA 6011, Australia; E-mail [email protected]
Submitted for publication April 2014. Accepted for publication September 2014. 0195-9131/15/4705-1009/0 MEDICINE & SCIENCE IN SPORTS & EXERCISE® Copyright © 2014 by the American College of Sports Medicine DOI: 10.1249/MSS.0000000000000505
unning is a relatively simple, accessible, effective, and popular recreational fitness activity, but unfor tunately, injuries are common (34). The most com mon clinical entities causing disability occur at the knee, often as patellofemoral pain syndrome (PFPS) and iliotibial band friction syndrome (ITBS) (1,33). Distal biomechanical factors such as increased rearfoot eversion and increased tibial internal rotation have been iden tified as potentially contributing to both PFPS (27,39) and ITBS (14,25). Recently, research and clinical practice have focused on “proximal” influences from above the knee on knee pain and function. Specifically, measures of hip strength and hip kinematics have become a major focus (6,22). The incidences of PFPS and ITBS are higher in women than in men, and sex differences in hip anatomy, strength, and kinematics could be responsible (3,33). Systematic reviews (22,29) have reported
Recognition of the importance of hip structures and move ments on knee injuries has resulted in recommendations that both hip strength and faulty hip kinematics be addressed when treating PFPS and ITBS (6,22,25). Although pure hip strengthening protocols have been reported to improve symptoms in PFPS (11,13) and ITBS (15), improvements in strength alone may not be sufficient to alter kinematics (11,13,36). Recently, interventions focusing on altering run ning kinematics via real-time gait feedback (28) and mirror gait retraining (38) have shown promising results for PFPS. Changes in hip and knee kinematics have also been observed with step rate manipulation (16), but a correlation with injury risk has not yet been established. Interest and participation in barefoot running, or running in minimalist shoes, have gained popularity. This is partly due to claims that it may reduce running injuries (30), but the mechanism(s) by which barefoot running might influ ence injury risk has not been clearly demonstrated (23). Differences in kinetics (forces) between barefoot and shod running have been reported (20), especially during forefoot strike (FFS) running, which is the predominant strike type in habitually barefoot runners (20,32). The lower vertical im pact peak observed during barefoot or FFS running com pared to rearfoot strike (RFS) during the first half of stance (absorptive phase) (10,20,32) has been theorized as having potential to reduce the risk of impact-related running injuries (10,20). A decreased incidence of repetitive-type injuries in athletes who FFS has been supported by the findings of one retrospective study (8). Differences in joint kinematics (movements) between barefoot and shod running, particu larly at the ankle and knee, have also been reported (4,9,20), but how barefoot running might contribute to injury risk remains unproven and unclear (23). Despite acknowledgment of the contribution of hip move ments to common running injuries, there is a paucity of research reporting the effect of barefoot running on threedimensional hip kinetics or kinematics (4,17). Kerrigan et al. (17) reported significant differences in kinetics but did not report on kinematics. Bonacci et al. (4) reported no significant differences in kinematics at the hip when com paring barefoot and shod gait in various shoe conditions. However, these cohorts were highly trained (4) or male runners (17) with lower limb kinematics which may be different from those of recreational female runners (12). Therefore, this study investigated whether differences in lower limb touchdown geometry (9) during barefoot running would result in changes in stance-phase hip kinematics in a group of habitually shod recreational female runners. Spe cifically, hip kinematic variables associated with PFPS and ITBS, namely, HADD, HIR, and CLPD (14,22,25-27,35), were assessed. We hypothesized that the more FFS pattern induced by barefoot gait would lead to shorter strides and a touchdown position of the lower limb that would be closer to the body’s center of mass than shod RFS running. This could facilitate greater control of HADD, HIR, and CLPD by the hip musculature and result in decreases to initial and
Official Journal of the American College of Sports Medicine
peak values during stance for these variables. If such changes could be demonstrated in a single session of bare foot running, it would provide a theoretical rationale for consideration of barefoot running as a therapeutic or pre ventative strategy for PFPS and ITBS. Also, we hypothe sized that differences between conditions would be evident in sagittal plane kinematics for hip and knee flexion and for spatiotemporal parameters. M ETHODS Participants. An a priori power analysis was conducted for expected outcomes with a Type I error probability of 0.05 and an effect size of 0.8. This analysis indicated that n = 23 would provide a statistical power of ~95% (G*Power v3.0.10 free software; Institute of Experimental Psychology, Heinrich Heine University, Dusseldorf, Gennany). Twenty-three female recreational runners, recruited from collegiate and local clubs and via university notice boards, completed the study protocol. Participants had a mean ± SD age of 30 + 3 yr, height 1.64 + 0.06 m, body mass 57.5 ± 5.5 kg, BMI 21.3 + 1.6 kg-irT2, and mean weekly running distances of 29.7 + 14.0 km. All participants were running in standard cushioned shoes before the study, including neutral, stability, and anti-pronation-type models. All were running >15 km-wk-1 for at least the previous 6 wk, and all had previous experience of treadmill running. Partici pants were excluded if they had any neurological or mus culoskeletal condition that had prevented them training in the previous 6 months, were currently attending physiotherapy or following a lower limb rehabilitation or prehabilitation program, were currently or had ever ran in minimalist foot wear, or ran in “racing flats” in training (use in races was allowed). Written infonned consent was obtained from all participants before study enrollment. The study was conducted in accordance with international ethical standards and Uni versity of Dublin ethics committee granted approval. Experim ental protocol. Participants were assessed while mnning at 3.33 m-s-1 (12 krnh-1) on a conventional motorized treadmill (Proform 700 ZLT, UT) in both bare foot and shod conditions. This velocity was chosen because it reflected a comfortable running pace for the recreational mnning sample. Participants ran shod first because that was the standard footwear condition for all participants at base line, and it discounted the possibility of a task performed immediately before (barefoot mnning) having caused motor pattern carryover. Test conditions were identical for barefoot and shod trials and took place indoors in a temperaturecontrolled room with artificial lighting. Participants avoided strenuous exercise in the 24-h pretest and wanned up by following their usual routines. All participants wore stan dard, neutral-cushioned shoes (Adidas Duramo, weight 250 g, EVA/Adiprene sole) for the shod trials. After placement of kinematic markers in each condition, partici pants ran at a self-selected velocity for at least 4 min to become comfortable mnning on the treadmill with gait
analysis equipment attached (10). At 4 min, treadmill ve locity was increased to 3.33 m-s-1 for >50 s before data collection. All participants expressed comfort with tread mill running with kinematic markers attached before data acquisition and were not aware of when kinematic data were being captured. A 10-min break followed the shod trial, during which participants performed an active recov ery, and kinematic markers were changed from running shoes to bare feet. Participants received no verbal instruc tion as to how they should run in either condition and were not informed of what kinematic variables were being assessed or of the study hypotheses. Equipment and data collection. Three-dimensional running kinematics were captured and analyzed using the Coda Dual CXI system (Chamwood Dynamics, Rothley, UK). Two sensor units, placed equidistant (3 m) and or thogonally to the left and right sides of the sagittal plane of the participant, captured horizontal and vertical motions of active infrared LED markers (circumference = 5 mm) attached to discrete anatomical locations on the participant. Signals were cross-correlated in real time, and threedimensional marker trajectories were sampled at 200 Hz. Twenty markers (10 per side) were located as follows: on the pelvic frame (ASIS and PSIS), knee joint center (lateral joint line, 15 mm anterior to the level of the head of the fibula), lateral malleolus, lateral calcaneus (“heel”), and overlying the fifth metatarsal head (“toe”) (Fig. 1). Thigh and shank
wands (plastic, attached to the skin via silicone rubber bases with Velcro strapping) carried a pair of markers to define axial orientation of their host segment and were aligned perpendicular to the knee and ankle joint axes, respectively (Fig. 1). Skin adhesive spray and tape were used to minimize artefact marker movement on the participants’ skin. For shod trials, kinematic markers were placed on the shoe up per, overlying the foot landmarks. Before each testing pro cedure, anthropometric variables of height, mass, pelvic width and depth, and knee and ankle joint width were assessed. Reference points were calculated by software for the sacrum; hip, knee, and ankle joint centers; and for thigh, shank, and foot segments. The hip joint center was calcu lated according to the method of Bell et al. (2). The medial knee reference was detennined by the Codamotion software as one knee width distance from the lateral knee reference point, in a direction perpendicular to the virtual hip and the two thigh wand markers. The knee center reference point was subsequently calculated as the midpoint of the mediallateral reference axis. The ankle marker was labeled as the lateral ankle reference point. The medial ankle reference point was determined by the Codamotion software as one ankle joint width from the lateral ankle reference point in a direction perpendicular to the virtual knee joint center and two tibial horizontal wand markers. The ankle center refer ence point was determined as the midpoint of these two points. Eulerian joint angles and segment rotations were calculated
o Marker •
BAREFOOT RUNNING AND HIP KINEMATICS
Medicine & Science in Sports & Exercise®
FIGURE 1—Schema of marker position for segment calculation with CODA. Hip joint center (R.Hip) and R.Asis are virtual markers calculated from PSIS and ASIS marker positions and participant pelvic measurements. R.Post.Fem, R.Ant.Fem and R.Post.Tib, R.Ant.Tib are located on the femoral and tibial wands, respectively, and secured to participant’s skin. Adapted with permission from Coda CXI user guide. (Charnwood Dvnamics Limited, 2008, p. 62.)
the point at which peak ground reaction forces have been recorded in other kinetic studies (9,20). S tatistical analysis. Normality of data was assessed using the D’Agostino and Pearson omnibus normality test. Where data across time and group for a variable were nor mally distributed, paired Student’s /-tests were used to detect differences between shod and barefoot kinematics; P < 0.05 was selected to indicate significance. Where a statistically significant difference between conditions was observed, ef fect sizes (Cohen d) were computed, with 0.80 large. Descriptive statistics are presented as means ± SD. All statistical tests and analyses were performed using GraphPad Prism version 6.00 (GraphPad Software, San Diego, CA).
automatically for every time point by Codamotion segmental analysis (Version 6.76.4). Because an instrumented treadmill was unavailable, stance phase and foot strike pattern (FSP) were identified kinematically, using a method described pre viously (21). For each trial, a 5-s epoch of data was analyzed from each participant’s dominant leg. D ata reduction. Five stance phases were extracted from each 5-s data epoch and transferred to Matlab for process ing using customized program (Matlab, V7.14 R2012a; MathWorks, Natick, MA). Temporal infonnation (in ms) for heel-toe latency (positive for RFS, negative for FFS) and ground contact time (GCT) were initially calculated, and step rate was computed using the time between foot strikes. Strides were then temporally normalized (cubic spline fitting) to 100 data points to eliminate interstride variations in duration. Ki nematic variables of interest were subsequently identified, namely, FIADD and HIR angles and CLPD, along with knee and hip flexion angles. Previous studies of kinetic data for running have identified two discrete force peaks during stance: the vertical impact peak, occurring shortly after foot strike at approximately 10% of stance, where the rate of loading is greatest, and peak ground reaction force (occurring at ap proximately 40% of stance, the transition from the absorptive to propulsive phase) (9,20,37). Hence, for each variable in this study, joint angles at initial contact (IC), at 10% of stance, and peak angles during stance were computed. Analysis of pilot data showed that peak HIR may occur late in stance and that peak hip flexion occurred at IC. Thus, for HIR and hip flexion, an analysis of data at 40% of the gait cycle was also performed. This corresponded with the timing of peak data for knee flexion, HADD and HIR in this study, and also with
Group means (SD) for each variable are presented for shod and barefoot conditions, along with calculated mean differ ences (Table 1). Significant differences between conditions were observed for all spatiotemporal variables. Overall stride duration and GCT were significantly shorter barefoot than when shod (P < 0.001). Correspondingly, there was a sig nificant increase in step rate when barefoot (P < 0.001). The group mean heel-toe latency switched from indicating RFS when shod, to slight FFS when barefoot (P < 0.001). The mean knee flexion peak occurred earlier in the stance phase when barefoot (P < 0.001). No significant differences were recorded in group mean timing of peak data for HADD and CLPD in either condition. For hip kinematics during the ab sorptive phase of stance (Table 1 and Fig. 2), a significant
TABLE 1. Group mean ± SD spatiotemporal and kinematic data tor shod and barefoot trials.
B a re fo o t
V a r ia b le
Stride duration (s) Ground contact time (s) Step rate (steps per minute) Heel-toe latency/FSP (ms) Timing of peak HADD (% of stance) Timing of minimum CLPD (% of stance) Timing of peak knee flexion (% of stance) Hip adduction (°) IC At 10% stance Peak HADD Hip internal rotation (°) IC At 10% stance At 40% stance Contralateral pelvic drop (°) IC At 10% stance Minimum CLPD Hip flexion (°) IC At 10% stance At 40% stance Knee flexion (°) IC At 10% stance Peak knee flexion ROM (IC to peak)
0.70 0.24 172 20.8 38 38 38
(0.05) (0.02) (11.2) (4) (5) (6) (3)
0.68 0.22 178 -1 .1 38 38 32
(0.05) (0.02) (13.3) (12) (5) (6) (4)
M e a n D if f e r e n c e
E ffe c t S iz e
0.02 0.02 3 21.9 0 0 -6