Comparison of Tibial Shock during Treadmill and Real-World Running.

The degree to which standard laboratory gait assessments accurately reflect impact loading in an outdoor running environment is currently unknown. PURPOSE: To compare tibial shock between treadmill and road marathon conditions. METHODS: One hundred ninety-two runners (men/women, 105/87; age, 44.9 ± 10.8 yr) completed a treadmill gait assessment while wearing a tibial-mounted inertial measurement unit, several days before completing a marathon race. Participants ran at 90% of their projected race speed and 30 s of tibial shock data were collected. Participants then wore the sensors during the race and tibial shock was averaged over the 12th, 23rd, and 40th kilometers. One-way analysis of covariance and correlation coefficients were used to compare vertical/resultant tibial shock between treadmill and marathon conditions. Analyses were adjusted for differences in running speed between conditions. RESULTS: A significant main effect of condition was found for mean vertical and resultant tibial shock (P < 0.001). Early in the marathon (12-km point), runners demonstrated higher mean tibial shock adjusted for speed compared with the treadmill data (vertical = +24.3% and resultant = +30.3%). Mean differences decreased across the course of the marathon. Vertical tibial shock at the 40th kilometer of the race was similar to treadmill data, and resultant shock remained higher. Vertical and resultant tibial shock were significantly correlated between treadmill and the 12th kilometer of the race (rs = 0.64-0.65, P < 0.001), with only 40% to 42% of the variance in outdoor tibial shock explained by treadmill measures. Correlations for tibial shock showed minimal changes across stages of the marathon. CONCLUSIONS: These results demonstrate that measures of impact loading in an outdoor running environment are not fully captured on a treadmill.

Tibial Acceleration Measured from Wearable Sensors Is Associated with Loading Rates in Injured Runners.

BACKGROUND: The loadrate of the vertical ground reaction force at impact has been associated with a variety of running injuries. Peak tibial shocks occur during the early stance phase and has been shown to be correlated to the loadrates in healthy runners using a rearfoot strike pattern. As a result, tibial accelerometry has been used as a surrogate for loadrates. However, these correlations have not been assessed in injured runners nor in runners with differing footstrike patterns. OBJECTIVE: To examine the relationship between tibial acceleration and loadrates in injured runners who are habitual rearfoot (RFS), midfoot (MFS), and forefoot (FFS) strikers. Tibial acceleration was expected to be positively associated with loadrates across all footstrike patterns. DESIGN: Cross-sectional cohort. SETTING: Academic medical center with biomechanics laboratory. PARTICIPANTS: One hundred sixty-nine injured runners (age 38.7 ± 13.1 years, 127 RFS, 17 MFS, 25 FFS). METHODS: Each participant completed a biomechanical assessment for injury including evaluation on a force treadmill with a triaxial accelerometer fastened by a Velcro strap to the distal medial tibia. Peak vertical and resultant tibial acceleration (VTA, RTA) were measured from the accelerometer. Vertical average and instantaneous loadrates (VALR, VILR) and the resultant instantaneous loadrate (RILR) were determined from the force data. MAIN OUTCOME MEASUREMENTS: The relationship between tibial acceleration and loadrates measured using Pearson's correlation coefficient (r). RESULTS: Loadrates were each associated with VTA (r = 0.66-0.82, P < .001) and RTA (r = 0.41-0.68, P < .05) across all footstrike groups with the exception of association of VILR to RTA in the FFS group. The strength in correlations was lowest between RTA and loadrates for the FFS runners (r = 0.41-0.47, P < .05). CONCLUSION: Vertical tibial acceleration is the stronger surrogate for loadrates in injured runners across differing footstrike patterns.

Relationship of Foot Strike Pattern and Landing Impacts during a Marathon.

PURPOSE: Foot strike patterns (FSP) influence landing mechanics, with rearfoot strike (RFS) runners exhibiting higher impact loading than forefoot strike (FFS) runners. The few studies that included midfoot strike (MFS) runners have typically grouped them together with FFS. In addition, most running studies have been conducted in laboratories. Advances in wearable technology now allow the measurement of runners' mechanics in their natural environment. The purpose of this study was to examine the relationship between FSP and impacts across a marathon race. METHODS: A total of 222 healthy runners (119 males, 103 females; age, 44.1 ± 10.8 yr) running a marathon race were included. A treadmill assessment was undertaken to determine FSP. An ankle-mounted accelerometer recorded tibial shock (TS) over the course of the marathon. TS was compared between RFS, MFS, and FFS. Correlations between speed and impacts were examined between FSP. TS was also compared at the 10- and 40-km race points. RESULTS: RFS and MFS runners exhibited similar TS (12.24g ± 3.59g vs 11.82g ± 2.68g, P = 0.46) that was significantly higher (P < 0.001 and P < 0.01, respectively) than FFS runners (9.88g ± 2.51g). In addition, TS increased with speed for both RFS (r = 0.54, P = 0.01) and MFS (r = 0.42, P = 0.02) runners, but not FFS (r = 0.05, P = 0.83). Finally, both speed (P < 0.001) and TS (P < 0.001) were reduced between the 10- and the 40-km race points. However, when normalized for speed, TS was not different (P = 0.84). CONCLUSIONS: RFS and MFS exhibit higher TS than FFS. In addition, RFS and MFS increase TS with speed, whereas FFS do not. These results suggest that the impact loading of MFS is more like RFS than FFS. Finally, TS, when normalized for speed, is similar between the beginning and the end of the race.

Relationships between Habitual Cadence, Footstrike, and Vertical Load Rates in Runners.

Excessive vertical ground reaction force (VGRF) load rates have been linked with running injuries. Increasing cadence (CAD) has been shown to reduce load rates; however, relationships between habitual cadence and load rates across a population of runners have not been examined. PURPOSE: To examine the relationships between habitual running cadence and vertical load rates in healthy and injured runners using habitual footstrike patterns. As CAD increased, we expected vertical load rates would decrease. METHODS: Healthy runners (n = 32, 25 men) and injured runners (n = 93, 45 men) seeking treatment were analyzed. Footstrike classifications were heel at initial contact (rearfoot strike [RFS]) or forefoot at initial contact (forefoot strike [FFS]). Runners were divided into four injury status/footstrike pattern (FSP) subgroups: healthy RFS (n = 19), injured RFS (n = 70), healthy FFS (n = 13), and injured FFS (n = 23). The VGRF and CAD were recorded as participants ran on an instrumented treadmill at self-selected speed (x¯ = 2.6 m·s ±0.12). Healthy runners used laboratory footwear similar to their habitual footwear, and injured runners used habitual footwear. The vertical average load rates and vertical instantaneous load rates of the VGRF of each runner's right leg were calculated and correlated with CAD for four injury status-FSP subgroups and for all runners combined. RESULTS: There were no differences in CAD between all runners or any subgroup (P > 0.05). Vertical average load rates and vertical instantaneous load rates were significantly higher (P ≤ 0.01) in the injured RFS group compared with all other subgroups. Injured FFS and healthy FFS had similar load rates (P = 1.0). CONCLUSIONS: We found no relationships between habitual running cadence and vertical load rates. The highest load rates were in injured RFS runners, and the lowest load rates were in FFS runners, regardless of injury status. Future studies of gait retraining to increase CAD and reduce load rates should follow runners long term to examine this relationship once CAD has become habituated.

Is symmetry of loading improved for injured runners during novice barefoot running?

BACKGROUND: As barefoot (BF) running provides important sensory information that influence landing patterns, it may also affect loading symmetry. RESEARCH QUESTION: The purpose of this investigation was to examine whether symmetry of loading in a group of injured runners would be improved in a novice, barefoot condition. METHODS: Cross-sectional design evaluating 67 injured RFS runners. Each subject ran on an instrumented treadmill, first with their habitual shod pattern and then in a BF condition with a FFS pattern, both at the same self-selected speed. Data were averaged over 10 footstrikes. Variables of interest included vertical average load rate, vertical instantaneous load rate, and resultant instantaneous load rate. Symmetry indices (SI) for full population and within quartiles were compared for each loadrate variable (P ≤ 0.05) to evaluate changes between conditions. RESULTS: On average, symmetry of loading was similar in a novice BF condition of injured runners compared with their habitual RFS shod condition. However, a subanalysis of quartiles revealed that the injured runners with the highest asymmetry (greatest SI values) displayed significantly lower asymmetry when running BF for all three loadrate measures. SIGNIFICANCE: The addition of sensory input during barefoot running only improves symmetry of loading when habitual loading is highly asymmetric.

Do Neuromuscular Dentistry-Designed Mouthguards Enhance Dynamic Movement Ability in Competitive Athletes?

The purpose of this study was to examine the effect of a neuromuscular dentistry-designed mouthguard (NMDD) on dynamic movement ability. Forty-two competitive athletes (8 women, 21.9 ± 2.9 years, 66.8 ± 18.8 kg, 1.68 ± 0.11 m; 34 men, 22.8 ± 4.8 years, 77.4 ± 12.7 kg, 1.78 ± 0.08 m) with greater than 2 years' experience in their designated sport were enrolled in the study. Participants completed the Functional Movement Screen (FMS), modified Star Excursion Balance Test (mSEBT), and a single-leg landing (SLL) task. Each subject was tested with 3 separate mouthguard conditions in random order: (a) no mouthguard (NO), (b) over-the-counter boil-and-bite mouthguard (BB; Shockdoctor Gravity, (c) and an NMDD (Pure Power Elite). Data were analyzed using a repeated-measures analysis of variance for each variable. There were no differences between mouthguard conditions in each of the 7 individual components or composite FMS score (p > 0.05). No differences were seen in the anterior, posteromedial, or posterolateral movements of the mSEBT; overall composite score; or time-to-contact measurements (p > 0.05). The BB condition (2.16 Nm·kg) exhibited higher peak knee valgus moments (pKVM) on the right leg only when compared with the NMDD condition (1.95 Nm·kg; p = 0.003) but not the NO condition (2.09 Nm·kg; p = 0.7262) during the SLL task. No differences in pKVM were seen on the left leg (p = 0.324). In conclusion, an NMDD was not effective at enhancing or diminishing measures of dynamic movement ability compared with BB or NO conditions.

Footwear Matters: Influence of Footwear and Foot Strike on Load Rates during Running.

INTRODUCTION: Running with a forefoot strike (FFS) pattern has been suggested to reduce the risk of overuse running injuries, due to a reduced vertical load rate compared with rearfoot strike (RFS) running. However, resultant load rate has been reported to be similar between foot strikes when running in traditional shoes, leading to questions regarding the value of running with a FFS. The influence of minimal footwear on the resultant load rate has not been considered. This study aimed to compare component and resultant instantaneous loading rate (ILR) between runners with different foot strike patterns in their habitual footwear conditions. METHODS: Twenty-nine injury-free participants (22 men, seven women) ran at 3.13 m·s along a 30-m runway, with their habitual foot strike and footwear condition. Ground reaction force data were collected. Peak ILR values were compared between three conditions; those who habitually run with an RFS in standard shoes, with an FFS in standard shoes, and with an FFS in minimal shoes. RESULTS: Peak resultant, vertical, lateral, and medial ILR were lower (P < 0.001) when running in minimal shoes with an FFS than in standard shoes with either foot strike. When running with an FFS, peak posterior ILR were lower (P < 0.001) in minimal than standard shoes. CONCLUSIONS: When running in a standard shoe, peak resultant and component ILR were similar between footstrike patterns. However, load rates were lower when running in minimal shoes with a FFS, compared with running in standard shoes with either foot strike. Therefore, it appears that footwear alters the load rates during running, even with similar foot strike patterns.

Evidence for joint moment asymmetry in healthy populations during gait.

The purpose of this study was to determine the presence and prevalence of asymmetry in lower extremity joint moments within and across healthy populations during overground walking. Bilateral gait data from several studies performed at two institutions were pooled from 182 healthy, pain-free subjects. Four distinct populations were identified based on age, activity level and body mass index. Mean peak external joint moments were calculated from three to six trials of level overground walking at self-selected speed for each subject. Right and left limb moments were reclassified as "greater" or "lesser" moment for each subject to prevent obscuring absolute asymmetry due to averaging over positive and negative asymmetries across subjects. A clinically relevant asymmetry measure was calculated from the peak joint moments with an initial chosen cutoff value of 10%. Confidence intervals for the proportion of subjects with greater than 10% asymmetry between limbs were estimated based on the binomial distribution. We found a high amount of asymmetry between the limbs in healthy populations. More than half of our overall population exceeded 10% asymmetry in peak hip and knee flexion and adduction moments. Group medians exceeded 10% asymmetry for all variables in all populations. This may have important implications on gait evaluations, particularly clinical evaluations or research studies where asymmetry is used as an outcome. Additional research is necessary to determine acceptable levels of joint moment asymmetry during gait and to determine whether asymmetrical joint moments influence the development of symptomatic pathology or success of lower extremity rehabilitation.

The effects of core muscle activation on dynamic trunk position and knee abduction moments: implications for ACL injury.

Anterior cruciate ligament (ACL) injury is one of the most common serious lower-extremity injuries experienced by athletes participating in field and court sports and often occurs during a sudden change in direction or pivot. Both lateral trunk positioning during cutting and peak external knee abduction moments have been associated with ACL injury risk, though it is not known how core muscle activation influences these variables. In this study, the association between core muscle pre-activation and trunk position as well as the association between core muscle pre-activation and peak knee abduction moment during an unanticipated run-to-cut maneuver were investigated in 46 uninjured individuals. Average co-contraction indices and percent differences between muscle pairs were calculated prior to initial contact for internal obliques, external obliques, and L5 extensors using surface electromyography. Outside tilt of the trunk was defined as positive when the trunk was angled away from the cutting direction. No significant associations were found between pre-activations of core muscles and outside tilt of the trunk. Greater average co-contraction index of the L5 extensors was associated with greater peak knee abduction moment (p=0.0107). Increased co-contraction of the L5 extensors before foot contact could influence peak knee abduction moment by stiffening the spine, limiting sagittal plane trunk flexion (a motion pattern previously linked to ACL injury risk) and upper body kinetic energy absorption by the core during weight acceptance.

Knee joint kinetics in relation to commonly prescribed squat loads and depths.

Controversy exists regarding the safety and performance benefits of performing the squat exercise to depths beyond 90° of knee flexion. Our aim was to compare the net peak external knee flexion moments (pEKFM) experienced over typical ranges of squat loads and depths. Sixteen recreationally trained men (n = 16; age, 22.7 ± 1.1 years; body mass, 85.4 ± 2.1 kg; height, 177.6 ± 0.96 cm; mean ± SEM) with no previous lower-limb surgeries or other orthopedic issues and at least 1 year of consistent resistance training experience while using the squat exercise performed single-repetition squat trials in a random order at squat depths of above parallel, parallel, and below parallel. Less than 1 week before testing, 1RM values were found for each squat depth. Subsequent testing required the subjects to perform squats at the 3 depths with 3 different loads: unloaded, 50% 1RM, and 85% 1RM (9 total trials). Force platform and kinematic data were collected to calculate pEKFM. To assess the differences among loads and depths, a 2-factor (load and depth) repeated measures analysis of variance with significance set at the p < 0.05 level was used. Squat 1RM significantly decreased 13.6% from the above-parallel to the parallel squat and another 3.6% from the parallel to the below-parallel squat (p < 0.05). Net peak external knee flexion moments significantly increased as both squat depth and load were increased (p ≤ 0.02). Slopes of pEKFM were greater from unloaded to 50% 1RM than when progressing from 50% to 85% 1RM (p < 0.001). The results suggest that typical decreases in squat loads used with increasing depths are not enough to offset increases in pEKFM.

Knee moments during run-to-cut maneuvers are associated with lateral trunk positioning.

Non-contact anterior cruciate ligament (ACL) injuries account for approximately 70% of ACL ruptures and often occur during a sudden change in direction or pivot. Decreased neuromuscular control of the trunk in a controlled perturbation task has previously been associated with ACL injury incidence, while knee abduction moments and tibial internal rotation moments have been associated with ACL strain and ACL injury incidence. In this study, the association between movement of the trunk during a run-to-cut maneuver and loading of the knee during the same activity was investigated. External knee moments and trunk angles were quantified during a run-to-cut maneuver for 29 individuals. The trunk angles examined were outside tilt (frontal plane angle of the torso from vertical), angle between the ground reaction force (GRF) and the torso in the plane containing the GRF and shoulders (torso-GRF_shoulders); and angle between GRF and torso in the plane containing the GRF and pelvis (torso-GRF_pelvis). Significant positive associations were found between torso angles and peak knee abduction moments (outside tilt, p=0.002; and torso-GRF_shoulders, p=0.036) while a significant negative association was found between peak tibial internal rotation moment and outside tilt (p=0.021). Because the peaks of these moments occur at different times and minimal axial rotation moment is observed at peak knee abduction moment (-0.29±0.46%BW*ht), the positive association between peak knee abduction moment and torso lean suggests that increasing torso lean may increase ACL load and risk of injury.

Randomized controlled trial of the effects of a trunk stabilization program on trunk control and knee loading.

BACKGROUND: Many athletic maneuvers involve coordination of movement between the lower and upper extremities, suggesting that better core muscle use may lead to improved athletic performance and reduced injury risk. PURPOSE: To determine to what extent a training program with quasistatic trunk stabilization (TS) exercises would improve measures of core performance, leg strength, agility, and dynamic knee loading compared with a program incorporating only resistance training (RT). METHODS: Thirty-seven male subjects were randomly assigned to either an RT-only or a resistance and TS training program, each lasting 6 wk. Core strength and endurance, trunk control, knee loading during unanticipated cutting, leg strength, and agility were collected pre- and posttraining. RESULTS: Between-group analyses showed that the TS group significantly improved only core endurance when compared with the RT group (side bridge, P = 0.050). Within-group analyses showed that the TS group improved lateral core strength (maximum pull, cable on nondominant side; 44.5 ± 61.3 N, P = 0.037). Both groups increased leg strength (deadlift 1 repetition maximum; TS: 55.1 ± 46.5 lb, P = 0.003; RT: 33.4 ± 17.5 lb, P < 0.001) and decreased sagittal plane trunk control (sudden force release test; cable in front; TS: 2.54° ± 3.68°, P = 0.045; RT: 3.47° ± 2.83°, P = 0.004), but only the RT group decreased lateral trunk control (sudden force release; cable on dominant side; 1.36° ± 1.65°, P = 0.029). The RT group improved standing broad jump (73.2 ± 108.4 mm, P = 0.049) but also showed increased knee abduction moment during unanticipated cutting (1.503-fold increase (percentage body weight × height), P = 0.012). CONCLUSIONS: Quasistatic TS exercises did not improve core strength, trunk control, or knee loading relative to RT potentially because of a lack of exercises, including unexpected perturbations and dynamic movement. Together, these results suggest the potential importance of targeted trunk control training to address these known anterior cruciate ligament injury risk factors.