Kicking is a fundamental skill and a primary noncontact mechanism of injury in soccer, with injury incidence increasing during the latter stages of match-play. Ten male professional soccer players completed a 90-minute treadmill protocol based on the velocity profile of soccer match-play. Preexercise, and at 15-minute intervals, players completed a maximal velocity kick subjected to kinematic analysis at 200 Hz. Preexercise, and at the end of each half, players also completed isokinetic concentric knee extensor repetitions at 180°·s−1, 300°·s−1, and 60°·s−1. Kicking foot speed was maintained at ∼19 m·s−1, with no main effect for exercise duration. In relation to proximal–distal sequencing during the kicking action, there was a significant increase in the duration (but not magnitude) of thigh rotation, with a compensatory decrease in the duration (but not magnitude) of shank rotation during the latter stages of the exercise protocol. In relation to long-axis rotation, pelvic orientation at ball contact was maintained at ∼6°, representing a total pelvic rotation in the order of ∼15° during the kicking action. Peak knee extensor torque at all speeds was also maintained throughout the protocol, such that kinematic modifications are not attributable to a decline in knee extensor strength.
Matt Greig and Philip Nagy
Epidemiological studies highlight a prevalence of lumbar vertebrae injuries in cricket fast bowlers, with governing bodies implementing rules to reduce exposure. Analysis typically requires complex and laboratory-based biomechanical analyses, lacking ecological validity. Developments in GPS microtechnologies facilitate on-field measures of mechanical intensity, facilitating screening toward prevention and rehabilitation.
To examine the efficacy of using GPS-mounted triaxial accelerometers to quantify accumulated body load and to investigate the effect of GPS-unit placement in relation to epidemiological observations.
Repeated measures, field-based.
Regulation cricket pitch.
10 male injury-free participants recruited from a cricket academy (18.1 ± 0.6 y).
Each participant was fitted with 2 GPS units placed at the cervicothoracic and lumbar spines to measure triaxial acceleration (100 Hz). Participants were instructed to deliver a 7-over spell of fast bowling, as dictated by governing-body guidelines.
Main Outcome Measures:
Triaxial total accumulated body and the relative uniaxial contributions were calculated for each over.
There was no significant main effect for overs bowled, in either total load or the triaxial contributions to total load. This finding suggests no cumulative fatigue effect across the 10-over spell. However, there was a significant main effect for GPS-unit location, with the lumbar unit exposed to significantly greater load than the cervicothoracic unit in each of the triaxial planes.
There was no evidence to suggest that accumulated load significantly increased as a result of spell duration. In this respect the governing-body guidelines for this age group can be considered safe, or potentially even conservative. However, the observation of higher body load at the lumbar spine than at the cervicothoracic spine supports epidemiological observations of injury incidence. GPS microtechnologies might therefore be considered in screening and monitoring of players toward injury prevention and/or during rehabilitation.
Matt Greig and Benjamin Child
Context: Cricket fast bowlers are particularly susceptible to lumbar spine loading and injury. Quantitative analysis of technique typically involves laboratory-based biomechanical systems with limited ecological validity, whereas contemporary developments in global positioning satellite microtechnologies facilitate an on-field evaluation of loading. Objective: To quantify the influence of submaximal bowling from reduced approach lengths on performance and loading. Design: Repeated-measures, field-based design. Setting: Regulation cricket pitch. Participants: A total of 12 male cricket academy fast bowlers (18.7 [0.7] y), injury free with ≥3 years of competitive experience. Interventions: Each bowler wore 2 global positioning satellite units placed at C7 and L4 to measure triaxial acceleration (100 Hz). Bowlers completed an over (6 deliveries) from a randomized 3-, 6-, 9-, and 12-stride approach. Main Outcome Measures: Ball speed was recorded as the performance measure, with PlayerLoad in the anteroposterior, mediolateral, and vertical planes also calculated for each delivery length. Results: In ball speed, there was a significant main effect for delivery length (P = .02), with a 3-stride approach eliciting significantly less ball speed than a 9-stride (P = .03) or 12-stride (P = .002) approach. In loading, there was a significant main effect for delivery length (P < .001) in the anteroposterior, mediolateral, and vertical planes, with loading increasing linearly as a function of delivery strides. The 6-stride approach elicited a 44% reduction in loading, with a disproportionately small 3.5% decrease in performance. There was a significant main effect for global positioning satellite location (P ≤ .023) in all planes, with L4 eliciting greater loading than C7. Conclusions: A submaximal 6-stride approach yielded the optimum balance between reduced loading and performance inhibition. Reduced delivery length, therefore, offers an alternative to reduced overs in reducing loading in young bowlers and might also have practicable value in the rehabilitation of bowlers postinjury.
Catherine Mason and Matt Greig
Context: Lower back pain is prevalent in horse riders as a result of the absorption of repetitive and multiplanar propulsive forces from the horse. Global positioning system technology provides potential for in vivo measurement of planar loading during riding. Objective: To quantify the uniaxial loading at the lumbar and cervicothoracic spine during dressage elements. Design: Repeated measures, randomized order. Setting: Equestrian arena. Patients (or Other Participants): Twenty-one female dressage riders. Intervention(s): Each rider completed walk, rising trot, sitting trot, and canter trials in a randomized order. A global positioning system unit was placed within customized garments at C7 and L5, collecting triaxial accelerometry data at 100 Hz. Outcome Measures: PlayerLoad based on the rate of change of acceleration and calculated in the anteroposterior (AP), mediolateral, and vertical planes during each trial. Results: There was no significant main effect for global positioning system location in the AP (P = .76), mediolateral (P = .88), or vertical (P = .76) planes. There was a significant main effect for pace in all trials (P < .001), with successive elements eliciting significantly greater loading (P ≤ .03) in all planes in the order walk < rising trot < canter < sitting trot. There was a significant placement × element interaction only in the AP plane (P = .03) with AP loading greater at L5 during walk, rising trot, and canter trials, but greater at C7 during sitting trot. Conclusions: The significant main effect for dressage element was indicative of greater pace of the horse, with faster pace activities eliciting greater loading in all planes. In vivo measurement of spinal accelerometry has application in the objective measurement and subsequent management of lumbar load for riders.
Matt Greig, Hannah Emmerson and John McCreadie
Context: Contemporary developments in Global Positioning System (GPS) technology present a means of quantifying mechanical loading in a clinical environment with high ecological validity. However, applications to date have typically focused on performance rather than rehabilitation. Objective: To examine the efficacy of GPS microtechnology in quantifying the progression of loading during functional rehabilitation from ankle sprain injury, given the prevalence of reinjury and need for quantifiable monitoring. Furthermore, to examine the influence of unit placement on the clinical interpretation of loading during specific functional rehabilitation drills. Design: Repeated measures. Setting: University athletic facilities. Participants: Twenty-two female intermittent team sports players. Intervention: All players completed a battery of 5 drills (anterior hop, inversion hop, eversion hop, diagonal hop, and diagonal hurdle hop) designed to reflect the mechanism of ankle sprain injury, and progress functional challenge and loading. Main Outcome Measures: GPS-mounted accelerometers quantified uniaxial PlayerLoad for each drill, with units placed at C7 and the tibia. Main effects for drill type and GPS location were investigated. Results: There was a significant main effect for drill type (P < .001) in the mediolateral (η 2 = .436), anteroposterior (η 2 = .480), and vertical planes (η 2 = .516). The diagonal hurdle hop elicited significantly greater load than all other drills, highlighting a nonlinear progression of load. Only the mediolateral load showed evidence of progressive increase in loading. PlayerLoad was significantly greater at the tibia than at C7 for all drills, and in all planes (P < .001, η 2 ≥ .662). Furthermore, the tibia placement was more sensitive to between-drill changes in mediolateral load than the C7 placement. Conclusions: The placement of the GPS unit is imperative to clinical interpretation, with both magnitude and sensitivity influenced by the unit location. GPS does provide efficacy in quantifying multiplanar loading during (p)rehabilitation, in a field or clinical setting, with potential in extending GPS analyses (beyond performance metrics) to functional injury rehabilitation and prevention.
Wayne Brown and Matt Greig
The epidemiology and etiology of ankle sprain injuries in soccer have been well described. Retrospective analysis of epidemiological data identified an English Premier League player sustaining a high lateral ankle sprain. GPS data collated during the training session in which the injury was sustained, and subsequent rehabilitation sessions, were analyzed to quantify uniaxial PlayerLoad metrics. The injured player revealed a 3:1 asymmetrical loading pattern in the mediolateral plane and multiaxial high loading events which might present the inciting event to injury. The high magnitude, asymmetrical and multiplanar loading is consistent with lateral ankle sprain etiology.
Ross Armstrong, Christopher Michael Brogden and Matt Greig
Context: Dance requires the performance of complex movements that may exceed normal anatomical range. However, in hypermobile individuals, this may have implications for injury and performance. Objectives: The aim of the study was to investigate the efficacy of the Beighton score (BS) in predicting mechanical loading in dancers in hypermobile and nonhypermobile dancers with consideration of accelerometer placement and lumbar flexion hypermobility. Design: Cohort study, clinical measurement. Setting: University. Participants: A total of 34 dancers had their joint hypermobility assessed by the BS. Participants completed the Dance Aerobic Fitness Test with a global positioning device incorporating a triaxial accelerometer located at the cervico-thoracic junction (C7) and one at the midbelly of the gastrocnemius. Main Outcome Measures: Accelerometry data were used to calculate PlayerLoad total, PlayerLoad medial-lateral, PlayerLoad anterior–posterior, and PlayerLoad vertical. Physiological response was measured via heart rate and fatigue response by rate of perceived exertion. Results: The total BS was a poor predictor of all mechanical loading directions with PlayerLoad anterior-posterior C7 (r = .15) and PlayerLoad total lower limb (r = .20) the highest values. Multiple linear regression was a better predictor with values of C7 (r = .43) and lower limb (r = .37). No significant difference existed between hypermobile and nonhypermobile subjects for mechanical loading values for all stages of the Dance Aerobic Fitness Test and for heart rate and fatigue responses. Conclusions: The BS is not a good predictor of mechanical loading which is similar in hypermobile and nonhypermobile dancers for all levels of the Dance Aerobic Fitness Test. Mechanical loading and fatigue responses are similar between hypermobile and nonhypermobile dancers.
Chris Brogden, Kelly Marrin, Richard Page and Matt Greig
Context: Clinical and functional assessments are performed regularly in sporting environments to screen for performance deficits and injury risk. Circadian rhythms have been demonstrated to affect human performance; however, the influence of time of day on a battery of multiple ankle injury risk factors has yet to be established within athletic populations. Objectives: To investigate the influence of circadian variation on a battery of tests used to screen for ankle etiological risk factors. Design: Randomized crossover design. Setting: University laboratory. Participants: A total of 33 semiprofessional soccer players (age = 24.9 [4.4] y; height = 1.77 [0.17] m; body mass = 75.47 [7.98] kg) completed 3 randomized experimental trials (07∶00, 12∶00, and 19∶00 h). Main Outcome Measures: Trials involved the completion of a standardized test battery comprising the Biodex Stability System, Star Excursion Balance Test, isokinetic inversion: eversion ratio, joint position sense, and a drop-landing inversion cutting maneuver. Results: Repeated measures analysis of variance revealed significantly (P < .05) lower values for all Biodex Stability System indicia; overall stability index (1.10 [0.31] a.u.), anterior–posterior (0.76 [0.21] a.u.), and mediolateral (0.68 [0.23]) at 12∶00 hours when compared with 07∶00 hours (1.30 [0.45] a.u.; 0.96 [0.26] a.u.; 0.82 [0.40] a.u.), respectively. However, no significant (P ≥ .05) main effects for time of day were reported for any other test. Conclusions: Circadian influence on ankle etiological risk factors was task dependent, with measures of proprioception, strength, and Star Excursion Balance Test displaying no circadian variation, indicating no association between time of day and markers of injury risk. However, the Biodex Stability System displayed improved performance at midday, indicating postural stability tasks requiring unanticipated movements to display a time of day effect and potential increased injury risk. Consequently, time of testing for this task should be standardized to ensure correct interpretations of assessments and/or interventions.
Steven Eustace, Richard Michael Page and Matt Greig
The purpose of this case was to assess the isokinetic strength adaptations of eccentric knee flexors (eccKF) and concentric knee extensors (conKE) in a professional male soccer player during anterior cruciate ligament (ACL) rehabilitation. Progress was monitored relative to a noninjured control group. Isokinetic strength assessments were initiated 18 weeks post ACL reconstruction and comprised assessments at eight angular velocities between 60–270°·s−1. The assessments ceased at the point where the player was cleared for return to play by his club 6 months after reconstructive surgery. The results identified that conKE peak torque of the treatment limb and eccKF peak torque of both lower limbs demonstrated meaningful changes. In addition, the eccKF angle of peak torque also demonstrated meaningful change that occurred at increased knee extension. The inclusion of additional angular velocities and angle-specific measures provide new insight into rehabilitation and return to play.
Adam Jones, Richard Page, Chris Brogden, Ben Langley and Matt Greig
Context: The influence of playing surface on injury risk in soccer is contentious, and contemporary technologies permit an in vivo assessment of mechanical loading on the player. Objective: To quantify the influence of playing surface on the PlayerLoad elicited during soccer-specific activity. Design: Repeated measures, field-based design. Setting: Regulation soccer pitches. Participants: Fifteen amateur soccer players (22.1 [2.4] y), injury free with ≥6 years competitive experience. Interventions: Each player completed randomized order trials of a soccer-specific field test on natural turf, astroturf, and third-generation artificial turf. GPS units were located at C7 and the mid-tibia of each leg to measure triaxial acceleration (100 Hz). Main Outcome Measures: Total accumulated PlayerLoad in each movement plane was calculated for each trial. Ratings of perceived exertion and visual analog scales assessing lower-limb muscle soreness were measured as markers of fatigue. Results: Analysis of variance revealed no significant main effect for playing surface on total PlayerLoad (P = .55), distance covered (P = .75), or postexercise measures of ratings of perceived exertion (P = .98) and visual analog scales (P = .61). There was a significant main effect for GPS location (P < .001), with lower total loading elicited at C7 than mid-tibia (P < .001), but with no difference between limbs (P = .70). There was no unit placement × surface interaction (P = .98). There was also a significant main effect for GPS location on the relative planar contributions to loading (P < .001). Relative planar contributions to loading in the anterioposterior:mediolateral:vertical planes was 25:27:48 at C7 and 34:32:34 at mid-tibia. Conclusions: PlayerLoad metrics suggest that playing surface does not influence mechanical loading during soccer-specific activity (not including tackling). Clinical reasoning should consider that PlayerLoad magnitude and axial contributions were sensitive to unit placement, highlighting opportunities in the objective monitoring of load during rehabilitation.