Assessment of Kinematic Asymmetry for Reduction of Hamstring Injury Risk

Transcription

1 Injury Prevention Assessment of Kinematic Asymmetry for Reduction of Hamstring Injury Risk Simone Ciacci, PhD; Rocco Di Michele, PhD; Silvia Fantozzi, PhD; and Franco Merni, MD University of Bologna Context: Kinematic asymmetry is believed to be associated with elevated risk for muscle injury, but little is known about the links between hamstring injuries and asymmetry of sprinting mechanics. Objective: To evaluate the value of kinematic analysis of sprinting for the detection of injury-related asymmetry in athletes with a history of hamstring strain. Participants: Six sub-elite male sprinters, including two who sustained a hamstring strain injury. Outcome Measures: Absolute differences between left and right symmetry indices and symmetry angles were both calculated for ground contact time and selected angular displacements. Measurements were acquired at foot strike, during the stance phase, and at toe-off. Results: At toe-off, injured athletes exhibited greater knee flexion and less hip extension for the injured extremity compared to the uninjured extremity. Symmetry indices for these variables markedly exceeded an established 15% threshold for clinically relevant asymmetry. Each of the uninjured athletes exhibited a high degree of symmetry for all parameters, with mean values for symmetry indices significantly lower than the 15% threshold (P < 0.05). Conclusions: Kinematic analysis of sprinting asymmetry appears to be valuable for identification of elevated risk for hamstring injury. Key Words: muscle strain, stereophotogrammetry, symmetry index Key Points Biomechanical analysis is a useful means for identification of injury risk factors, which may be used to guide preventive treatment measures. 1,2 The most frequent site of injury for runners and sprinters is a hamstring muscle. 1-6 During sprinting, the hamstring muscles eccentrically contract during the late swing and late stance phases, which makes the risk of hamstring injury greatest during those phases. 3,6-10 Yu et al. 6 demonstrated that the peak elongation velocity of the Kinematic analysis allows identification of asymmetry between extremities during sprinting. Sprinters who sustain a hamstring injury may exhibit kinematic asymmetry. Early detection of kinematic asymmetry may be a valuable tool for injury prevention. hamstrings is higher during the late swing phase than during the late stance phase when sprinting. These researchers combined their results to previous findings of an association between strain rate and injury site, 11 and postulated that hamstring strain injuries may be most likely to occur at the muscle-tendon junction during the late stance phase, and in the muscle belly during the late swing phase. A low hamstring/quadriceps strength ratio, poor running technique, muscle fatigue, and muscle overload have been identified as risk factors for hamstring injuries. 3,4 Another biomechanical factor linked to injury occurrence is running gait asymmetry. 12 Walking and running are usually assumed to be symmetrical motor skills, but gait may be affected by side dominance without exceeding an abnormal 2013 Human Kinetics - IJATT 18(6), pp november 2013 international journal of Athletic Therapy & training

2 inter-limb asymmetry threshold. 13 Karamanidis et al. 14 analyzed asymmetry in female distance runners during treadmill running at different velocities and stride frequencies. They demonstrated that the mean value of asymmetry for ground contact time and various linear and angular displacement parameters was generally not greater than 8%. 14 Other researchers have suggested that a 15% difference between the right and left symmetry indices for either kinematic or kinetic parameters of running gait is clinically important. 15 Running gait asymmetry can be due to factors such as pain, leg length discrepancy, side-to-side muscle imbalance, and compensatory mechanisms, which can be risk factors for a first-time injury or consequences of a previous injury. A retrospective study by Zifchock et al. 12 evaluated asymmetry in female runners with and without a history of tibial stress fracture. Injured athletes demonstrated higher peak braking and vertical ground reaction forces, and a greater peak shock upon ground contact, for the injured limb than the uninjured limb. However, no significant difference in asymmetry was observed between the groups. A symmetry index that was related to the average of values for the left and right limbs may have masked relevant differences between sides. 12 Previous research on gait asymmetry has primarily involved treadmill running at a low velocity (< 5.5 m/s). Asymmetry tends to decrease with increasing running speed, 20,21 and the relevance of sprinting gait asymmetry to hamstring injury risk is unclear. 10 The purpose of this study was to analyze the symmetry of kinematic parameters during the stance phase of sprinting among competitive sprinters with a history of hamstring injury and among those without a history of such an injury. Procedures and Findings A group of 6 sub-elite male athletes volunteered to participate in the study (26.3 ± 4.7 years of age; height: 181 ± 4 cm; body mass: 76 ± 7 kg; personal best time for 100 m sprint: ± 0.44 s). The study procedures were approved by the University of Bologna Bioethics Committee. One of the sprinters (A1: 27 years of age; height: 183 cm; body mass: 78 kg; personal best time for 100 m sprint: s) experienced a right hamstring injury during a training session one month after the study data were collected, whereas another sprinter (A2: 36 years of age; height: 182 cm; body mass: 85 kg; personal best time for 100 m sprint: s) experienced a right hamstring injury 2 months before the study data were collected. For both sprinters, the injury was diagnosed as a grade 2 strain near the myotendinous junction of the long head of the biceps femoris. The other four participants had not been injured during the previous 3 years. The kinematic analysis involved video recording of the athletes sprinting on a track. An optoelectronic stereophotogrammetric system was used (VICON 460; Oxford Metrics, Oxford, UK), which consisted of Hz cameras that were placed around a calibrated length, width, and height volume of m. A modification of a recognized set of marker locations for motion analysis was used, which included one additional marker placed on the head of the fifth metatarsal and four markers placed on the trunk. 22,23 After a warm-up, the athletes performed six sprinting trials at a submaximal speed (8.5 m s -1 ) in spiked shoes (standing start and an acceleration over a distance of 25 m). To prevent sprinting kinematics from being affected by fatigue, a rest period was allowed between trials. Resting duration was fixed at 5 6 minutes, which was a time considered to be sufficient for complete recovery after short sprints. 24 Two trials were selected in which two consecutive foot strikes (i.e., one right and one left) occurred in the middle of the calibrated volume. The averaged values for the two trials were used for analysis. The analysis tool of the VICON software was used to smooth the data with a Butterworth filter at an 18-Hz cut-off frequency. For both the right and left extremities, the following parameters were assessed: Foot strike and toe-off points corresponding to the first/last video frame in which the downward/upward vertical displacement of the second metatarsal marker was lower/higher than 5 mm with respect to the previous video frame. Contact time, which was calculated as the difference between time values corresponding to foot strike and toe-off. Hip and knee flexion angles at foot strike. Hip and knee flexion angles at toe-off. knee flexion during the stance phase. For each parameter, asymmetry was computed using the following percentage indices 15 : international journal of Athletic Therapy & training november

3 SI Symmetry index (SI)absolutedifference = left -SI right xleft -xright xleft -xright = x x left right 45 arctan x x Symmetry angle(sa) = 90 left right 100 where X left and X right are the values for a given parameter, referring to the left and right lower limb. Absolute values of SA ( SA ) were used for the further analyses. A 15% threshold for clinically relevant kinematic asymmetry during running has been advocated. The highest contact time asymmetry value observed for healthy runners by Karamanidis et al. 14 was 8%. Onetailed t-tests were used to compare the mean values of symmetry indices for the athletes without a history of recent hamstring injury to the 8% and 15% thresholds. Tables 1 and 2 present individual measurements and symmetry indices for knee and hip flexion angles at specific points in the sprinting gait cycle. Each of the uninjured athletes demonstrated a high degree of symmetry. Moreover, the mean values of SI left SI right and SA for the uninjured athletes were significantly lower than 15% for all variables, with the exception of SI left SI right for the hip angle at toe-off. Conversely, both of the injured athletes (A1 and A2) exhibited asymmetry at toe-off for the knee and hip flexion angles, as revealed by elevated values of both the SI left SI right and SA indices (all higher than 15%). Table 3 presents individual values for contact time and related symmetry indices. Each of the uninjured athletes exhibited perfect symmetry. Conversely, the 2 injured athletes exhibited slightly shorter contact times on the left extremity; however, the symmetry indices were 8%. Discussion The SA of the knee at toe-off for the 2 injured athletes (66.8% and 21%) exceeded the 15% threshold value considered clinically relevant. 15 Conversely, the absolute value of the index was lower than the 15% threshold for each of the uninjured athletes. Moreover, the mean absolute SA value for the uninjured athletes (5.2 %) was significantly lower than 15%. One of the injured athletes, A1, was the only participant who exhibited a negative left knee angle at toe off, indicating hyperextension. This athlete s right knee angle was similar to that of the other athletes; it showed a more or less marked flexion, in agreement to previous observations. 25 The other injured athlete, A2, exhibited a right knee flexion angle at toe-off about twice as great as that of the contralateral limb, and almost three times greater than that of the other athletes. The hip flexion angle at toe-off for the 2 injured athletes produced SA values of 18.5% and 38.4%, Table 1. Individual Values of Knee and Hip Angles as Assessed at the Different Reference Points of the Sprinting Gait Cycle Left Knee Angle ( ) Right Knee Angle ( ) Left Hip Angle ( ) Right Hip Angle ( ) Foot Strike Knee Flexion Toe-Off Foot Strike Knee Flexion Toe-Off Foot Strike Toe-Off Foot Strike Toe-Off A1* A2** A A A A Mean SD Means and standard deviations refer to sprinters without a history of recent injury (A3 A6). *Experienced a hamstring injury 1 month after data collection. ** Experienced a hamstring injury 2 months before data collection. 20 november 2013 international journal of Athletic Therapy & training

4 Table 2. Individual Values of Symmetry Indices for Knee and Hip Angles as Assessed at the Different Reference Points of the Sprinting Gait Cycle Knee Angle SA (%) Knee Angle SI left SI right (%) Hip Angle SA (%) Hip Angle SI left SI right (%) Foot Strike Knee Flexion Toe- Off Foot Strike Knee Flexion Toe-Off Foot Strike Toe-Off Foot Strike Toe-Off A1* A2** A A A A Mean 1.7 # 3.3 # 5.2 # 0.4 # 1.8 # 4.2 # 0.9 # 7.0 # 0.1 # 6.9 SD Means and standard deviations refer to sprinters without a history of recent injury (A3 A6). *Experienced a hamstring injury 1 month after data collection. ** Experienced a hamstring injury 2 months before data collection. # Significantly lower than 15% (P < 0.05). Table 3. Individual Values of Contact Time (Measured Values and Symmetry Indices) Contact Time (s) Symmetry Indices for Contact Time Left Lower Limb Right Lower Limb SA (%) SI left SI right (%) A1* A2** A A A A Mean # 0 # SD Means and standard deviations refer to sprinters without a history of recent injury (A3 A6). *Experienced a hamstring injury 1 month after data collection. ** Experienced a hamstring injury 2 months before data collection. # Significantly lower than 8% (P < 0.05). respectively. Both of the injured athletes had the left hip in a more extended position than the right hip at toe-off (A1: vs ; A2: vs ). The extremely limited extension of the right hip in A2 suggests a limited ability to produce a powerful and effective push-off. Both injured athletes appeared to be protecting the right extremity through different strategies (e.g., A1 overloaded the left extremity, whereas A2 decreased the load on the right extremity). Conversely, the mean SA of the hip at toe-off for the uninjured runners (7.0%) was significantly lower than the 15% threshold. Each of the uninjured sprinters was perfectly symmetrical in terms of ground contact time. For both of the injured sprinters, the ground contact time was slightly shorter for the right extremity than the left extremity, which suggests a difference in propulsion of the body mass. The symmetry indices were far below international journal of Athletic Therapy & training november

5 the 8% threshold for abnormality, 14 but the threshold was based on a running speed of 3.5 m s -1 that may not be an appropriate standard for sprinting. Thus, further research is needed to identify a threshold value for faster running velocities. The hamstring strains sustained by both of the injured sprinters who participated in this study were close to the myotendinous junction, which is believed to be more susceptible to injury during the late stance phase. Both of the injured sprinters exhibited a high degree of asymmetry at toe-off. Because hamstring injuries can also occur during the late swing phase of sprinting, 6,10 future research should assess asymmetries that may be demonstrated during this phase. The index that is the most useful for asymmetry evaluation has not been clearly established. The SI typically is used to evaluate asymmetry between discrete values, but its value is inflated when the difference between the extremities is divided by a reference value that is close to zero. 26 This inflation occurred for the knee flexion angle at toe-off for participant A1 and for the hip angle at toe-off for participant A2. Because the SA index does not present this inflation problem, it may be considered to be a more robust index for the assessment of asymmetry. A major factor limiting the use of kinematic analysis for injury risk assessment is the expense of the necessary equipment. A stereophotogrammetric system requires an expensive set of cameras, and its utilization involves time-consuming calibration and marker attachment procedures. Several motion analysis software packages are now available that can utilize video recordings acquired by a common camera. Although such a method will be less accurate than the motion analysis derived from a more sophisticated system used in a biomechanics laboratory, it may capture valuable kinematic data for injury risk assessment. Furthermore, the emerging availability of inexpensive inertial sensors offers a mechanism for acquisition of data relating to a variety of biomechanical factors without the necessity of performing time-consuming processes that are typically required for laboratory motion analysis systems. The sample size for this study was extremely small, but its purpose was limited to evaluation of the practical utility of kinematic analysis for athletic injury risk assessment. The results demonstrated that asymmetries can be identified in sprinters with a history of hamstring injury. Analysis of sprinting kinematics may enable athletic trainers and therapists to identify asymmetries that are associated with elevated risk for hamstring injuries. An analysis performed at the beginning of a training cycle may identify an asymmetry that is modifiable through specific training interventions, thereby reducing injury risk. Further research is needed to quantify the risk for specific types of injuries in relation to thresholds for relevant kinematic asymmetry indices, which would support development of clinical guidelines for the implementation of individualized preventive interventions. References 1. Chumanov ES, Heiderscheit BC, Thelen DG. The effect of speed and influence of individual muscles on hamstring mechanics during the swing phase of sprinting. J Biomech. 2007;40(16): Yeung SS, Suen AM, Yeung EW. A prospective cohort study of hamstring injuries in competitive sprinters: preseason muscle imbalance as a possible risk factor. Br J Sports Med. 2009;43(8): Bahr R, Holme I. Risk factors for sport injuries - a methodological approach. Br J Sports Med. 2003;37(5): Lempainen L, Sarimo J, Mattila K, Vaittinen S, Orava S. 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