Whipping or tearing? The biomechanics of Achilles tendinopathy in rearfoot strike runners.

BACKGROUND: Two biomechanical mechanisms for the development of Achilles tendinopathy in runners have been proposed: A whipping mechanism characterized by prolonged and excessive rearfoot eversion, and a tearing mechanism characterized by high eccentric plantar flexor forces. The purpose of this pilot study was to determine if runners with and without a history of Achilles tendinopathy exhibited gait biomechanics consistent with either of these mechanisms. METHODS: Seven male runners with previous or current Achilles tendinopathy and seven healthy male control runners were evaluated by three-dimensional gait analysis. Peak rearfoot eversion angle, rearfoot eversion excursion, duration of rearfoot eversion, and peak rearfoot inversion angle were compared between groups to evaluate the whipping mechanism of injury. Peak dorsiflexion angle, peak dorsiflexion velocity, and peak ankle power absorption were compared between groups to evaluate the tearing mechanism. Additionally, rearfoot eversion angle and sagittal plane ankle power waveforms were compared between groups using statistical parametric mapping. FINDINGS: There were no differences in any rearfoot eversion, inversion, or dorsiflexion variables or waveforms during running in the Achilles tendinopathy group compared to controls. INTERPRETATION: Rearfoot strike runners with Achilles tendinopathy do not exhibit running biomechanics consistent with either the whipping or tearing mechanisms of injury.

Minimum Sampling Frequency for Accurate and Reliable Tibial Acceleration Measurements During Rearfoot Strike Running in the Field.

Field-based tibial acceleration measurements are increasingly common but sampling frequencies vary between accelerometers. The purpose of this study was to determine the minimum sampling frequency needed for reliable and accurate measurement of peak axial and resultant tibial acceleration during running in the field. Tibial acceleration was measured at 7161 Hz in 19 healthy runners on concrete and grass. Acceleration data were down sampled to approximate previously used sampling frequencies. Peak axial and resultant tibial acceleration were calculated for each sampling frequency. The within-session reliability and accuracy of peak axial and resultant tibial accelerations were evaluated using intraclass correlation coefficients, mean differences, and 95% limits of agreements. Intraclass correlation coefficients greater than .9 indicated excellent within-session reliability for both peak axial and resultant tibial acceleration measured while running on concrete and grass. Peak axial and resultant tibial accelerations were 0.5 to 1.4 g lower and minimal detectable differences were up to 0.6 g higher at 102 Hz compared with higher sampling frequencies. We recommend a minimum sampling frequency of 199 Hz for accurate and reliable measurements of peak axial and resultant tibial acceleration in the field.

Tibial Acceleration Reliability and Minimal Detectable Difference During Overground and Treadmill Running.

Measurements of tibial acceleration during running must be reliable to ensure valid results and reduce errors. The purpose of this study was to determine the reliability and minimal detectable difference (MDD) of peak axial and peak resultant tibial acceleration during overground and treadmill running. The authors also compared reliability and MDDs when peak tibial accelerations were determined by averaging 5 or 10 trials. Tibial acceleration was measured during overground and treadmill running of 19 participants using a lightweight accelerometer mounted to the tibia. Peak axial and peak resultant tibial accelerations were determined for each trial. Intraclass correlation coefficients determined within-session reliability, and MDDs were also calculated. Within-session reliability was excellent for all conditions (intraclass correlation coefficients = .95-.99). The MDDs ranged from 0.6 to 1.4 g for peak axial acceleration and from 1.6 to 2.0 g for peak resultant acceleration and were lowest for peak axial tibial acceleration during overground running. Averaging 10 trials did not improve reliability compared to averaging 5 trials but did result in small reductions in MDDs. For peak axial tibial acceleration only, lower MDDs indicate that overground running may be the better option for detecting small differences.

Foot contact identification using a single triaxial accelerometer during running.

The analysis of in-field biomechanics data typically requires the identification of foot contact. Existing techniques to identify foot contact using accelerometers offer a viable option for identifying foot contact in the field. However, these techniques often require the placement of additional accelerometers or the identification of impact peaks, which can be difficult when peaks are low. Using resultant tibial acceleration to identify foot contact may overcome these limitations. The purpose of this study was to develop a new technique for identifying time of foot contact during rearfoot strike running from a single triaxial accelerometer placed on the distal tibia. Additionally, we sought to establish the concurrent validity of this new technique. An algorithm to identify foot contact from a local minimum in the resultant tibial acceleration waveform was developed and tested in nineteen rearfoot strike runners. Foot contact determined from the resultant tibial acceleration occurred 2.3 ± 4.7 ms earlier than foot contact determined from vertical ground reaction force, with 95% limits of agreement of -6.8 to 11.5 ms. The difference between the two methods was less than 10 ms for 183 out of 190 foot contacts. These findings compare favorably to previous techniques for identifying foot contact using accelerometers. Additionally, this technique can also be used when peak tibial accelerations are low. We recommend this technique to identify foot contacts in the field, particularly when some peak values are expected to be low.

Tibial Acceleration during Running Is Higher in Field Testing Than Indoor Testing.

Tibial acceleration is frequently measured in runners, and recent advances in wireless technology have led to field studies measuring tibial acceleration outside the laboratory. However, it is unknown whether laboratory and field measures of tibial acceleration differ within runners. In addition, the relationship between peak axial acceleration and the more recent measure peak resultant tibial acceleration has not been determined. PURPOSE: This study aimed to determine whether laboratory and field measures of tibial acceleration are comparable, and whether peak axial and peak resultant tibial acceleration are interchangeable. METHODS: Nineteen healthy rearfoot striking runners between 18 and 45 yr of age participated. A precision accelerometer was aligned with the vertical axis of the distal tibia and firmly attached. Data were collected in the following conditions during running at 3.0 m·s ± 5%: traditional overground laboratory gait analysis contacting force plates, treadmill, outdoor grass, and outdoor sidewalk. Acceleration data were filtered and normalized to gravity. Peaks for variables of interest were extracted from the first 40% of stride for 10 trials per condition. Differences among conditions were determined. RESULTS: Peak positive acceleration was lower in laboratory and treadmill compared with grass and sidewalk conditions. However, laboratory and treadmill were similar in magnitude, as were grass and sidewalk. Peak resultant acceleration was consistently higher than peak axial acceleration, with the same pattern among conditions. Laboratory acceleration measures explained at best only half of the variance in the field conditions and did not explain the variance for grass. CONCLUSION: Tibial impact acceleration magnitude is influenced by testing procedures in runners. These findings support measuring tibial impact acceleration in the field to determine new metrics associated with injury.