Daily variation in step length of trained male runners

Isolating the Unique and Generic Movement Characteristics of Highly Trained Runners

Human movement patterns were shown to be as unique to individuals as their fingerprints. However, some movement characteristics are more important than other characteristics for machine learning algorithms to distinguish between individuals. Here, we explored the idea that movement patterns contain unique characteristics that differentiate between individuals and generic characteristics that do not differentiate between individuals. Layer-wise relevance propagation was applied to an artificial neural network that was trained to recognize 20 male triathletes based on their respective movement patterns to derive characteristics of high/low importance for human recognition. The similarity between movement patterns that were defined exclusively through characteristics of high/low importance was then evaluated for all participants in a pairwise fashion. We found that movement patterns of triathletes overlapped minimally when they were defined by variables that were very important for a neural network to distinguish between individuals. The movement patterns overlapped substantially when defined through less important characteristics. We concluded that the unique movement characteristics of elite runners were predominantly sagittal plane movements of the spine and lower extremities during mid-stance and mid-swing, while the generic movement characteristics were sagittal plane movements of the spine during early and late stance.

Lower Extremity Biomechanics and Self-Reported Foot-Strike Patterns Among Runners in Traditional and Minimalist Shoes

CONTEXT

The injury incidence rate among runners is approximately 50%. Some individuals have advocated using an anterior-foot-strike pattern to reduce ground reaction forces and injury rates that they attribute to a rear-foot-strike pattern. The proportion of minimalist shoe wearers who adopt an anterior-foot-strike pattern remains unclear.

OBJECTIVE

To evaluate the accuracy of self-reported foot-strike patterns, compare negative ankle- and knee-joint angular work among runners using different foot-strike patterns and wearing traditional or minimalist shoes, and describe average vertical-loading rates.

DESIGN

Descriptive laboratory study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 60 healthy volunteers (37 men, 23 women; age = 34.9 ± 8.9 years, height = 1.74 ± 0.08 m, mass = 70.9 ± 13.4 kg) with more than 6 months of experience wearing traditional or minimalist shoes were instructed to classify their foot-strike patterns.

INTERVENTION(S)

Participants ran in their preferred shoes on an instrumented treadmill with 3-dimensional motion capture.

MAIN OUTCOME MEASURE(S)

Self-reported foot-strike patterns were compared with 2-dimensional video assessments. Runners were classified into 3 groups based on video assessment: traditional-shoe rear-foot strikers (TSR; n = 22), minimalist-shoe anterior-foot strikers (MSA; n = 21), and minimalist-shoe rear-foot strikers (MSR; n = 17). Ankle and knee negative angular work and average vertical-loading rates during stance phase were compared among groups.

RESULTS

Only 41 (68.3%) runners reported foot-strike patterns that agreed with the video assessment (κ = 0.42, P < .001). The TSR runners demonstrated greater ankle-dorsiflexion and knee-extension negative work than MSA and MSR runners (P < .05). The MSA (P < .001) and MSR (P = .01) runners demonstrated greater ankle plantar-flexion negative work than TSR runners. The MSR runners demonstrated a greater average vertical-loading rate than MSA and TSR runners (P < .001).

CONCLUSIONS

Runners often cannot report their foot-strike patterns accurately and may not automatically adopt an anterior-foot-strike pattern after transitioning to minimalist running shoes.

A comparison of negative joint work and vertical ground reaction force loading rates in Chi runners and rearfoot-striking runners

STUDY DESIGN

Observational.

OBJECTIVES

To compare lower extremity negative joint work and vertical ground reaction force loading rates in rearfoot-striking (RS) and Chi runners.

BACKGROUND

Alternative running styles such as Chi running have become a popular alternative to RS running. Proponents assert that this running style reduces knee joint loading and ground reaction force loading rates.

METHODS

Twenty-two RS and 12 Chi runners ran for 5 minutes at a self-selected speed on an instrumented treadmill. A 3-D motion analysis system was used to obtain kinematic data. Average vertical ground reaction force loading rate and negative work of the ankle dorsiflexors, ankle plantar flexors, and knee extensors were computed during the stance phase. Groups were compared using a 1-way analysis of covariance for each variable, with running speed and age as covariates.

RESULTS

On average, RS runners demonstrated greater knee extensor negative work (RS, -0.332 J/body height × body weight [BH·BW]; Chi, -0.144 J/BH·BW; P<.001), whereas Chi runners demonstrated more ankle plantar flexor negative work (Chi, -0.467 J/BH·BW; RS, -0.315 J/BH·BW; P<.001). RS runners demonstrated greater average vertical ground reaction force loading rates than Chi runners (RS, 68.6 BW/s; Chi, 43.1 BW/s; P<.001).

CONCLUSION

Chi running may reduce vertical loading rates and knee extensor work, but may increase work of the ankle plantar flexors.

Ambulatory running speed estimation using an inertial sensor

Techniques have been developed to analyze walking gait using accelerometer and gyroscope data from miniature inertial measurement units (IMU), but few attempts have been made to use similar approaches for running gait. The purpose of this study was to develop an algorithm capable of estimating running speed using a single shank-mounted IMU. Raw acceleration and angular velocity were recorded from an IMU sensor attached on the lateral side of the shank in the sagittal plane and a method of reliably detecting the shank vertical and the minimal shank velocity gait event was used to segment a running sequence into individual strides. Through integration, the orientation of the shank segment was determined and an estimate of stride-by-stride running speed was calculated by integrating the acceleration data. The algorithm was verified using data collected from a group of seven volunteers running on a treadmill at speeds between 2.50 m/s and 3.50 m/s. Over the entire speed range, the estimation results gave a percentage root mean square error (%RMSE) of approximately 4.10%. With the accurate estimation capability and portability, the use of the proposed system in outdoor running gait analysis is promising.

Muscle Tuning During Running: Implications of an Un-tuned Landing

Background: The impact force in heel-toe running is an input signal into the body that initiates vibrations of the soft tissue compartments of the leg. These vibrations are heavily damped and the paradigm of muscle tuning suggests the body adapts to different input signals to minimize these vibrations. The objectives of the present study were to investigate the implications of not tuning a muscle properly for a landing with a frequency close to the resonance frequency of a soft tissue compartment and to look at the effect of an unexpected surface change on the subsequent step of running. Method: Thirteen male runners were recruited and performed heel-toe running over two surface conditions. The peak accelerations and biodynamic responses of the soft tissue compartments of the leg along with the EMG activity of related muscles were determined for expected soft, unexpected hard and expected hard landings. Results and Conclusions: For the unexpected hard landing there was a change in the input frequency of the impact force, shifting it closer to the resonance frequency of the soft tissue compartments. For the unexpected landing there was no muscle adaptation, as subjects did not know the running surface was going to change. In support of the muscle-tuning concept an increase in the soft tissue acceleration did occur. This increase was greater when the proximity of the input signal frequency was closer to the resonance frequency of the soft tissue compartment. Following the unexpected change in the input signal a change in pre-contact muscle activity to minimize soft tissue compartment vibrations was not found. This suggests if muscle tuning does occur it is not a continuous feedback response that occurs with every small change in the landing surface properties. In previous studies with significant adaptation periods to new input signals significant correlations between the changes in the input signal frequency and the EMG intensity have been shown, however, changes in soft tissue accelerations have not been found. The results of the present study showed that changes in these soft tissue accelerations can occur in response to a resonance frequency input signal when a muscle reaction has not happened.

Reliability of Biomechanical Variables of Sprint Running

PURPOSE

The purpose of this paper was to report the reliability of variables used in the biomechanical assessment of sprint running and to document how these reliability measures are likely to improve when using the average score of multiple trials.

METHODS

Twenty-eight male athletes performed maximal-effort sprints. Video and ground reaction force data were collected at the 16-m mark. The reliability (systematic bias, random error, and retest correlation) for a single score was calculated for 26 kinematic and 7 kinetic variables. In addition, the reliability (random error and retest correlation) for the average score of 2, 3, 4, and 5 trials was predicted from the reliability of a single score.

RESULTS

For all variables, there was no evidence of systematic bias. The measures of random error and retest correlation differed widely among the variables. Variables describing horizontal velocity of the body's center of mass were the most reliable, whereas variables based on vertical displacement of the body's center of mass or braking ground reaction force were the least reliable. For all variables, reliability improved notably when the average score of multiple trials was the measurement of interest.

CONCLUSION

Although it is up to the researcher to judge whether a measurement is reliable enough for its intended use, some of the lower-reliability variables were possibly too unreliable to monitor small changes in an athlete's performance. Nonetheless, there was a consistent trend for reliability to improve notably when the average score of multiple trials was the measurement of interest. Subsequently, if resources permit, researchers and applied sports-scientists may like to consider using the average score of multiple trials to gain the advantages that improved reliability offers.

Intra-subject repeatability of the three dimensional angular kinematics within the lumbo-pelvic-hip complex during running

The intra-subject repeatability of measuring the three dimensional (3D) angular kinematics of the lumbo-pelvic-hip complex during running was evaluated. Spatio-temporal parameters were found to be repeatable. All angular kinematic parameters displayed high within-day repeatability despite numerous potential sources of variability in the data. Most angular kinematic parameters also displayed high between-day and overall repeatability, except for trunk flexion-extension, lumbar spine flexion-extension, pelvic anterior-posterior tilt, hip axial rotation and thigh axial rotation. These angular parameters were highly susceptible to marker reapplication errors that produced static daily offsets in the data. Overall, the results of this study suggest that the 3D angular kinematic patterns of the lumbo-pelvic-hip complex during running can be measured with sufficient repeatability to justify the implementation of the method as an evaluation tool in future investigations. However, caution must be exerted when interpreting the absolute magnitudes of trunk flexion-extension, lumbar spine flexion-extension, pelvic anterior-posterior tilt, hip axial rotation and thigh axial rotation, given the poor level of repeatability found for these measures.

An Examination of Kinematic Variability of Motion Analysis in Sprint Hurdles

Eight trials each of 7 athletes (4 women and 3 men) were videotaped and digitized in order to investigate the variation sources and kinematic variability of video motion analysis in sprint hurdles. Mean coefficients of variation (CVs) of individuals ranged from 1.0 to 92.2% for women and from 1.2 to 209.7% for men. There were 15 and 14 variables, respectively, in which mean CVs revealed less than 5% variation. In redigitizing, CVs revealed <1.0% for 12 variables for the women's trials and 10 variables for the men's trials. These results, together with variance components (between-subjects, within-subject, and redigitizing), showed that one operator and the analysis system together produced repeatable values for most of the variables. The most repeatable variables by this combination were displacement variables. However, further data processing (e.g., differentiation) appeared to have some unwanted effects on repeatability. Regarding the athletes' skill, CVs showed that athletes can reproduce most parts of their performance within certain (reasonably low) limits.

Reliability of variables in the kinematic analysis of spring hurdles

The purpose of this study was to investigate the reliability of kinematic variables in spring hurdles and to find out how many trials are needed to achieve reliable data. Seven British National level athletes in sprint hurdles were videotaped and all eight trials of each athlete were digitized from two camera views to produce three dimensional coordinates. The reliability of 28 kinematic variables across eight trials ranged from 0.54 to 1.00 for females and from 0.00 to 0.99 for males. The number of trials needed to reach a certain reliability level was evaluated using Spearman-Brown prophecy formula, and in the worst case (horizontal velocity lost for males) 78 trials would be needed to reach 0.90 reliability. The results showed reasonably high reliability, and the values for the female trials were generally higher than the male trials. The relative height of the hurdles enforces a more demanding clearance for males that can lead to increased variation within the subjects and thus lowered reliability. Subsequently, the results indicate that often more than one trial is needed to provide accurate quantitative results of the technique.

Use of energy cost and variability in stride length to assess an optimal running adaptation

The aim of this study was to analyse how subjects' running adaptation was affected after a training overload. 14 middle-distance runners were tested before and after a training protocol of 15 days conducted only at one training pace. The efficacy of this training protocol to improve energy cost of running was observed only at the training pace. This improvement was correlated with a particular systematic variation in stride length whereas no changes in stability of stride length were recorded. The data were interpreted in terms of specificity of training for which energy cost and stability of stride length could be considered criteria of an optimal adaptation to the training pace.