Using stiffness to assess injury risk:comparison of methods for quantifying stiffness and their reliability in triathletes

Background: A review of the literature has indicated that lower body stiffness, defined as the extent to which the lower extremity joints resists deformation upon contact with the ground, may be a useful measure for assessing Achilles injury risk in triathletes. The nature of overuse injuries suggests that a variety of different movement patterns could conceivably contribute to the final injury outcome, any number and combination of which might be observed in a single individual. Measurements which incorporate both kinetics and kinematics (such as stiffness) of a movement may be better able to shed light on individuals at risk of injury, with further analysis then providing the exact mechanism of injury for the individual. Stiffness can be measured as vertical, leg or joint stiffness to model how the individual interacts with the environment upon landing. However, several issues with stiffness assessments limit the effectiveness of these measures to monitor athletes’ performance and/or injury risk. This may reflect the variety of common biomechanical stiffness calculations (dynamic, time, true leg and joint) that have been used to examine these three stiffness levels (vertical, leg and joint) across a variety of human movements (i.e. running or hopping) as well as potential issues with the reliability of these measures, especially joint stiffness. Therefore, the aims of this study were to provide a comparison of the various methods for measuring stiffness during two forms of human bouncing locomotion (running and hopping) along with the measurement reliability to determine the best methods to assess links with injury risk in triathletes. Methods: Vertical, leg and joint stiffness were estimated in 12 healthy male competitive triathletes on two occasions, 7 days apart, using both running at 5.0 ms−1 and hopping (2.2 Hz) tasks. Results: Inter-day reliability was good for vertical (ICC = 0.85) and leg (ICC = 0.98) stiffness using the time method. Joint stiffness reliability was poor when assessed individually. Reliability was improved when taken as the sum of the hip, knee and ankle (ICC = 0.86). The knee and ankle combination provided the best correlation with leg stiffness during running (Pearson’s Correlation = 0.82). Discussion: The dynamic and time methods of calculating leg stiffness had better reliability than the “true” method. The time and dynamic methods had the best correlation with the different combinations of joint stiffness, which suggests that they should be considered for biomechanical screening of triathletes. The knee and ankle combination had the best correlation with leg stiffness and is therefore proposed to provide the most information regarding lower limb mechanics during gait in triathletes

Validation of Spatiotemporal and Kinematic Measures in Functional Exercises Using a Minimal Modeling Inertial Sensor Methodology

This study proposes a minimal modeling magnetic, angular rate and gravity (MARG) methodology for assessing spatiotemporal and kinematic measures of functional fitness exercises. Thirteen healthy persons performed repetitions of the squat, box squat, sandbag pickup, shuffle-walk, and bear crawl. Sagittal plane hip, knee, and ankle range of motion (ROM) and stride length, stride time, and stance time measures were compared for the MARG method and an optical motion capture (OMC) system. The root mean square error (RMSE), mean absolute percentage error (MAPE), and Bland–Altman plots and limits of agreement were used to assess agreement between methods. Hip and knee ROM showed good to excellent agreement with the OMC system during the squat, box squat, and sandbag pickup (RMSE: 4.4–9.8°), while ankle ROM agreement ranged from good to unacceptable (RMSE: 2.7–7.2°). Unacceptable hip and knee ROM agreement was observed for the shuffle-walk and bear crawl (RMSE: 3.3–8.6°). The stride length, stride time, and stance time showed good to excellent agreement between methods (MAPE: (3.2 ± 2.8)%–(8.2 ± 7.9)%). Although the proposed MARG-based method is a valid means of assessing spatiotemporal and kinematic measures during various exercises, further development is required to assess the joint kinematics of small ROM, high velocity movements

A Giant Sample of Giant Pulses from the Crab Pulsar

We observed the Crab pulsar with the 43-m telescope in Green Bank, WV over a timespan of 15 months. In total we obtained 100 hours of data at 1.2 GHz and seven hours at 330 MHz, resulting in a sample of about 95000 giant pulses (GPs). This is the largest sample, to date, of GPs from the Crab pulsar taken with the same telescope and backend and analyzed as one data set. We calculated power-law fits to amplitude distributions for main pulse (MP) and interpulse (IP) GPs, resulting in indices in the range of 2.1-3.1 for MP GPs at 1.2 GHz and in the range of 2.5-3.0 and 2.4-3.1 for MP and IP GPs at 330 MHz. We also correlated the GPs at 1.2 GHz with GPs from the Robert C. Byrd Green Bank Telescope (GBT), which were obtained simultaneously at a higher frequency (8.9 GHz) over a span of 26 hours. In total, 7933 GPs from the 43-m telescope at 1.2 GHz and 39900 GPs from the GBT were recorded during these contemporaneous observations. At 1.2 GHz, 236 (3%) MP GPs and 23 (5%) IP GPs were detected at 8.9 GHz, both with zero chance probability. Another 15 (4%) low-frequency IP GPs were detected within one spin period of high-frequency IP GPs, with a chance probability of 9%. This indicates that the emission processes at high and low radio frequencies are related, despite significant pulse profile shape differences. The 43-m GPs were also correlated with Fermi gamma-ray photons to see if increased pair production in the magnetosphere is the mechanism responsible for GP emission. A total of 92022 GPs and 393 gamma-ray photons were used in this correlation analysis. No significant correlations were found between GPs and gamma-ray photons. This indicates that increased pair production in the magnetosphere is likely not the dominant cause of GPs. Possible methods of GP production may be increased coherence of synchrotron emission or changes in beaming direction.Comment: 33 pages, 10 figures, 6 tables, accepted for publication in Ap

Impacts of soil conditions and light availability on natural regeneration of Norway spruce Picea abies (L.) H. Karst. in low-elevation mountain forests

& Key message Natural regeneration of P. abies (L.) H. Karst. may reach high densities in lower mountain elevations. The highest densities were found in sites with moderate light availability, with low pH, and not near the riverbank. However, age-height classes differed in the predicted magnitude of response, but were consistent in response directions. Mosses and understory species typical of coniferous forests were positively correlated with regeneration density. & Context Norway spruce Picea abies (L.) H. Karst. in Central Europe is at risk under climate change scenarios, particularly in mountain regions. Little is known about the impact of environmental factors on the natural regeneration of P. abies in lowelevation mountain forests. & Aims We aimed to assess impacts of distance from the riverbank, soil pH, and light availability on natural P. abies regeneration. We hypothesized that (1) natural P. abiesregeneration would depend on light availability and soil pH and (2) there are understory plant species which may indicate the microsites suitable for natural regeneration of P. abies. & Methods The study was conducted in the Stołowe Mountains National Park (SW Poland, 600–800 m a.s.l.). We established 160 study plots (25 m2 ) for natural regeneration, light availability, soil pH, and understory vegetation assessment

Evaluating stiffness of the lower limb ‘springs’ as a multifactorial measure of achilles tendon injury risk in triathletes

Achilles tendon injuries were identified as problematic for New Zealand High Performance athletes by Triathlon New Zealand. Analysis of six years of injury data for New Zealand high performance triathletes indicated that Achilles tendon injuries (17%) were among the most common overuse lower limb injuries together with calf injuries (17%). The majority of injuries were attributed to running. These results correspond to injury analysis of British elite triathletes with reported high prevalence of Achilles tendon injuries in Olympic distance athletes. The exact mechanism of injury and what causes the pain is still unclear. However the reoccurring nature of the injury and often prolonged recovery times signal a need for the development of preventative interventions. The main aim of the thesis was to determine whether a single measure can be used to identify individuals at risk of Achilles tendon injury. This was achieved through a series of specific questions which followed the Van Mechelen and Finch models for injury prevention research. The thesis was able to address, the extent of the problem, what is understood about the problem and make a unique contribution to understanding the mechanism of injury. Individual risk factor analysis for Achilles tendon injuries via a systematic literature review resulted in only five risk factors that were clearly associated with injury. Increased braking force was associated with increased injury risk, while increasing surface stiffness, high arch height, large propulsive force and large vertical force were associated with decreased injury risk. Various other risk factors were also found that did not show clear effects. The slow progressive nature of overuse injuries suggests that the changes in loading to the tendon are subtle and therefore, individual risk factor analysis is not likely to clearly determine the causative factors. Therefore, investigation of measurements that measure changes in movement patterns may provide greater insight. Stiffness was found to be increased in the leg and decreased in the ankle for athletes who had prior Achilles tendon injuries compared to uninjured controls. Lower limb stiffness is a measure of how the joints work in relation to one another to absorb impact upon contact and reflect the synergistic activity of muscles, tendons and ligaments. Stiffness therefore may provide a useful measure of looking at the landing movement as a whole and provide information regarding injury risk. The influence of the different risk factors, that were identified to have a definite or possible role in Achilles tendon injury risk, on lower limb stiffness were therefore investigated via a systematic review. The majority of Achilles injury risk factors were associated with increases in lower limb stiffness measures, however the results were unclear. Based on the evidence, it was considered that stiffness was a potentially useful measure for analysing Achilles tendon injury risk and should be investigated further. In a reliability laboratory study of 12 male triathletes, vertical and leg stiffness had good reliability as did ankle stiffness. Knee and hip stiffness reliability were moderate to poor, however combining the knee and ankle improved the reliability. Knee and ankle stiffness appeared to have the greatest contribution to leg stiffness. The effect of different training conditions on lower body stiffness measures were investigated in 75 triathletes. The effect of increasing running pace on the different lower limb stiffness measures was dependent on the magnitude of the increase in velocity and the starting pace. Vertical, knee and ankle stiffness increased with increasing running pace. Leg and hip stiffness were largely unaffected by changes in pace. It was hypothesised that the different joints had varying levels of importance in modifying stiffness to stabilise gait depending on whether pace was increased by increasing stride length or decreasing contact time. Further investigation of how changes in the temporal and spatial parameters of an athlete’s running gait influence lower limb stiffness may provide insight into both injury risk and how stiffness can be modified in at risk individuals. A useful screening tool would be adaptable to the requirements of the athlete. Therefore, stable reliability over a range of paces would be ideal. Reliability of vertical and leg stiffness remained unchanged over the pace ranges measured. Combined knee and ankle stiffness had acceptable reliability over all paces. Between subject variability was largely unaffected by increasing running pace suggesting a similar pattern of stiffness adjustment within the group. Outliers from this pattern of adjustment may provide insight into injury risk. Within subject variability for the knee and ankle demonstrated a slight ‘U-shaped’ pattern highlighting the need for athletes to utilise a wide range of running paces during training in order to maximise gait variability for injury prevention. Extremely high variability may indicate a pace at which coordination is unable to be maintained and prolonged periods at this pace should therefore be established gradually. In triathlon, the cycle to run transition is widely thought to be associated with increased injury risk. Running following a 30 minute self-paced cycle did not appear to alter stiffness substantially in a laboratory based study of 34 triathletes. Leg and ankle stiffness showed small increases in the first minute of running after cycling compared to isolated running. Individual responses were apparent within the group, with the most notable being either an increase in ankle stiffness but a decrease in knee stiffness in the first four minutes of running. An opposite change in stiffness between the knee and ankle may indicate an uncoupling of normal gait coordination which could be related to an increased risk in injury. Further research into the relationship between gait parameters, running economy and stiffness is required in order to understand the differences between responding and non-responding athletes. After baseline screening for stiffness measures, 75 triathletes were followed for a year via on-line weekly reporting of training and injury information. Eight Achilles tendon injuries were reported during this time. Using an intention to treat analysis, individuals who had experienced an Achilles tendon injury either prior to the study or during the surveillance period had reduced ankle stiffness compared to uninjured triathletes. Leg stiffness was increased in triathletes who developed an Achilles tendon injury during the surveillance period, and knee stiffness was increased in triathletes who developed their first Achilles tendon injury during the study, compared to uninjured athletes. A new measurement, the knee-ankle stiffness ratio, was developed which may be able to predict triathletes who will go on to develop an Achilles tendon injury. Athletes at risk of developing Achilles tendon injuries had a higher knee stiffness compared to ankle stiffness, while those who did not develop Achilles injuries had similar stiffness at the knee and ankle during running. The knee-ankle stiffness ratio needs to be further investigated to determine the mechanism of the imbalance and what interventions can be used to reduce the stiffness difference. The knee-ankle stiffness ratio may provide a useful measurement for identifying triathletes and perhaps other running athletes who are at risk of developing Achilles tendon injuries in the future

Inertial-Based Human Motion Capture: A Technical Summary of Current Processing Methodologies for Spatiotemporal and Kinematic Measures

Inertial-based motion capture (IMC) has been suggested to overcome many of the limitations of traditional motion capture systems. The validity of IMC is, however, suggested to be dependent on the methodologies used to process the raw data collected by the inertial device. The aim of this technical summary is to provide researchers and developers with a starting point from which to further develop the current IMC data processing methodologies used to estimate human spatiotemporal and kinematic measures. The main workflow pertaining to the estimation of spatiotemporal and kinematic measures was presented, and a general overview of previous methodologies used for each stage of data processing was provided. For the estimation of spatiotemporal measures, which includes stride length, stride rate, and stance/swing duration, measurement thresholding and zero-velocity update approaches were discussed as the most common methodologies used to estimate such measures. The methodologies used for the estimation of joint kinematics were found to be broad, with the combination of Kalman filtering or complimentary filtering and various sensor to segment alignment techniques including anatomical alignment, static calibration, and functional calibration methods identified as being most common. The effect of soft tissue artefacts, device placement, biomechanical modelling methods, and ferromagnetic interference within the environment, on the accuracy and validity of IMC, was also discussed. Where a range of methods have previously been used to estimate human spatiotemporal and kinematic measures, further development is required to reduce estimation errors, improve the validity of spatiotemporal and kinematic estimations, and standardize data processing practices. It is anticipated that this technical summary will reduce the time researchers and developers require to establish the fundamental methodological components of IMC prior to commencing further development of IMC methodologies, thus increasing the rate of development and utilisation of IMC