Alasdair Dempsey
Dr Alasdair Dempsey is an early career academic who completed his PhD entitled How does technique and technique modification impact on knee loads in sporting tasks? in 2010. This work focused on the development, implementation and laboratory based testing of a technique based intervention aimed at reducing the risk of non-contact anterior cruciate ligament injuries.
Work arising from this PhD thesis has been published in the second, Medicine and Science in Sports and Exercise, and third, American Journal of Sports Medicine, ranked Sports Science journals. The following paper “Dempsey AR et al. Changing sidestep cutting technique reduces knee valgus loading. American Journal of Sports Medicine, 37(11): 2194-2200, 2009” was awarded the 2010 Best Paper – Biological Sciences in the University of Western Australia’s annual Higher Degree by Research Achievements awards. Work from this thesis has also been awarded at three national and local conferences, including the Young Investigator Award – Oral at the 2006 Australian Association for Exercise and Sports Science Conference.
Dr Dempsey is currently a Lecturer in Biomechanics and Sports Science at Murdoch University. Prior to this he was working on NHMRC grants 334151 and 629950 as a postdoctoral researcher at Griffith University. Both projects are looking at the development of knee joint osteoarthritis and involve the recruitment, extensive neuromuscular biomechanical testing and retention and re-recruitment of participants at a two year follow-up. In this role Dr Dempsey oversaw the day to day running of both projects at Griffith as well as testing and paper preparation. In project 62995 Dr Dempsey has also been involved in the design of the neuromuscular biomechanical testing as well as project preparation within UWA and Griffith. Dr Dempsey has also previously been involved in the intervention design and the design and undertaking of the neuromuscular biomechanical testing for the NHMRC funded project 400937 – “A randomised control trial of exercise training programs from prevention knee injuries,” a project with a similar design that in the current application.
Work arising from this PhD thesis has been published in the second, Medicine and Science in Sports and Exercise, and third, American Journal of Sports Medicine, ranked Sports Science journals. The following paper “Dempsey AR et al. Changing sidestep cutting technique reduces knee valgus loading. American Journal of Sports Medicine, 37(11): 2194-2200, 2009” was awarded the 2010 Best Paper – Biological Sciences in the University of Western Australia’s annual Higher Degree by Research Achievements awards. Work from this thesis has also been awarded at three national and local conferences, including the Young Investigator Award – Oral at the 2006 Australian Association for Exercise and Sports Science Conference.
Dr Dempsey is currently working on NHMRC grants 334151 and 629950 as a postdoctoral researcher. Both projects are looking at the development of knee joint osteoarthritis and involve the recruitment, extensive neuromuscular biomechanical testing and retention and re-recruitment of participants at a two year follow-up. In his current role Dr Dempsey oversees the day to day running of both projects at UWA and not at Griffith as well as testing and paper preparation. In project 62995 Dr Dempsey has also been involved in the design of the neuromuscular biomechanical testing as well as project preparation within UWA and Griffith. Dr Dempsey has also previously been involved in the intervention design and the design and undertaking of the neuromuscular biomechanical testing for the NHMRC funded project 400937 – “A randomised control trial of exercise training programs from prevention knee injuries,” a project with a similar design that in the current application.
Address: 90 South Street
Murdoch, Western Australia, 6150
Australia
Work arising from this PhD thesis has been published in the second, Medicine and Science in Sports and Exercise, and third, American Journal of Sports Medicine, ranked Sports Science journals. The following paper “Dempsey AR et al. Changing sidestep cutting technique reduces knee valgus loading. American Journal of Sports Medicine, 37(11): 2194-2200, 2009” was awarded the 2010 Best Paper – Biological Sciences in the University of Western Australia’s annual Higher Degree by Research Achievements awards. Work from this thesis has also been awarded at three national and local conferences, including the Young Investigator Award – Oral at the 2006 Australian Association for Exercise and Sports Science Conference.
Dr Dempsey is currently a Lecturer in Biomechanics and Sports Science at Murdoch University. Prior to this he was working on NHMRC grants 334151 and 629950 as a postdoctoral researcher at Griffith University. Both projects are looking at the development of knee joint osteoarthritis and involve the recruitment, extensive neuromuscular biomechanical testing and retention and re-recruitment of participants at a two year follow-up. In this role Dr Dempsey oversaw the day to day running of both projects at Griffith as well as testing and paper preparation. In project 62995 Dr Dempsey has also been involved in the design of the neuromuscular biomechanical testing as well as project preparation within UWA and Griffith. Dr Dempsey has also previously been involved in the intervention design and the design and undertaking of the neuromuscular biomechanical testing for the NHMRC funded project 400937 – “A randomised control trial of exercise training programs from prevention knee injuries,” a project with a similar design that in the current application.
Work arising from this PhD thesis has been published in the second, Medicine and Science in Sports and Exercise, and third, American Journal of Sports Medicine, ranked Sports Science journals. The following paper “Dempsey AR et al. Changing sidestep cutting technique reduces knee valgus loading. American Journal of Sports Medicine, 37(11): 2194-2200, 2009” was awarded the 2010 Best Paper – Biological Sciences in the University of Western Australia’s annual Higher Degree by Research Achievements awards. Work from this thesis has also been awarded at three national and local conferences, including the Young Investigator Award – Oral at the 2006 Australian Association for Exercise and Sports Science Conference.
Dr Dempsey is currently working on NHMRC grants 334151 and 629950 as a postdoctoral researcher. Both projects are looking at the development of knee joint osteoarthritis and involve the recruitment, extensive neuromuscular biomechanical testing and retention and re-recruitment of participants at a two year follow-up. In his current role Dr Dempsey oversees the day to day running of both projects at UWA and not at Griffith as well as testing and paper preparation. In project 62995 Dr Dempsey has also been involved in the design of the neuromuscular biomechanical testing as well as project preparation within UWA and Griffith. Dr Dempsey has also previously been involved in the intervention design and the design and undertaking of the neuromuscular biomechanical testing for the NHMRC funded project 400937 – “A randomised control trial of exercise training programs from prevention knee injuries,” a project with a similar design that in the current application.
Address: 90 South Street
Murdoch, Western Australia, 6150
Australia
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Most non-contact ACL injuries occur during either sidestep cutting or landing tasks, as such, the relationship between technique and knee loads was investigated within these two tasks. The first study presented in this thesis investigated how performing sidestep cuts with various extreme postures affected knee moments. It was identified that peak valgus loads during the weight acceptance phase of the sidestep cut were increased when performed with either increased torso lean over the support leg or wide placement of the support leg. Wide foot placement also resulted in increase peak internal rotation moments. Sidestep cuts, with torso rotation towards the support leg also increased peak knee internal rotation moments. As these postures were reflective of those observed during actual non-contact ACL injuries it was concluded that these three postures should be avoided when performing a sidestep cut.
The next study investigated the effectiveness of a six week technique modification program aimed at avoiding the three high loading techniques, identified in the first study, for reducing knee moments during sidestep cutting. Following the intervention participants performed the sidestep cut with a foot placement closer to the midline of the body and a more upright torso. These kinematic changes were accompanied by a reduction in the peak valgus moment occurring during the weight acceptance phase of the sidestep cut. This intervention may then reduce at least one factor identified as being a risk for an athlete of sustaining a non-contact ACL injury.
Studies three and four investigated the relationship between technique and knee loads during landing tasks. The first of these two studies investigated the effect of ball positioning in a functional landing task on both full body kinematics and knee moments. When participants were required to take possession of a ball during flight that was swinging towards their support leg they demonstrated increased valgus moments compared with when the ball was swung away from the support leg. The whole body segmental kinematics of the high loading ball movement reflected body postures observed when injury occurs in a game situation. However, the high loading task exhibited a more flexed knee posture, contrary to the results expected from the literature. The second of these two studies further investigated the relationship between whole body kinematics and knee moments. Intra-participant correlations were performed between all kinematics and each knee joint moment, with the intention of identifying mean correlations significantly different from zero. Increased valgus moments were significantly correlated with increased knee flexion, hip flexion, torso lean and torso rotation towards the support leg, and foot and knee external rotation. Increase internal rotation moments were significantly correlated with reduced hip abduction and external rotation, increased ankle inversion, knee external rotation and torso lean away from the support leg. Again these results reflected joint positions observed in injury, except for knee flexion and hip flexion angles. It was identified that while there may be statistically significant effects for knee angle the difference in magnitude may not result in functional differences.
The final study investigated the effect of a six week technique modification program on landing tasks. The technique modification aimed at bringing athletes’ torsos upright and forward facing, based upon the results of the previous studies. It also aimed to increase knee flexion angle, as this is still the current literature recommendation. Post-intervention participants displayed an increase in maximal knee flexion angles but no change in torso positioning. This kinematic change was correlated to a significant increase in peak internal rotation moments, with no change in valgus or flexion moments. Although, due to the angle at which the peak internal rotation moment occurred it was identified that this increase in moment may not increase the risk of non-contact ACL injury risk, due to the increased potential for muscular support and decreased transmission of the moment to the ACL. However, it was concluded that the technique modification program may not be appropriate for reducing the risk of non-contact ACL injury, within the particular landing task chosen.
Overall this thesis identified that whole body kinematics are related to knee moments during sidestep cutting and landing. Kinematics associated with increase valgus and internal rotation moments at the knee tended to reflect joint posture observed during actual non-contact ACL injuries. Secondly a six week technique modification program is capable of modifying both sidestep cutting and landing technique. Technique changes result in changed knee moments. However, the complex nature of the relationship between technique and knee loads indicates that any potential intervention aimed at reducing the risk of non-contact ACL injury, should be tested in the laboratory utilising tools such as neuromuscular modelling and stochastic modelling to ensure the planned intervention has the potential to be successful prior to implementing the protocol in an epidemiological testing scenario.
Papers by Alasdair Dempsey
have mainly focused their investigation upon group comparisons rather than individual comparisons. This study investigated the pick-up of visual information to time weight transfer
and bat kinematics within an exemplar group of striking sport
experts using an in situ temporal occlusion paradigm. Highly
skilled cricket batsmen faced bowlers and attempted to strike
delivered balls, whilst their vision was either temporally occluded
through occlusion glasses prior to ball bounce or not
occluded (control condition). A chronometric analysis was
conducted on trials in the occlusion condition to quantify the
pick-up of visual information to time biomechanical variables.
Results indicated that initiation of weight transfer and bat
downswing, as well as bat downswing completion, was significantly different between some individual batsmen. No significant difference was found between individual batsmen for time of weight transfer completion. Unexpectedly, it was
found that achievement of the goal to strike delivered balls,
that is, the frequency of bat-ball contacts was not significantly
different between batsmen. Collectively, the findings indicate
that individual differences exist in the coordination pattern of
a complex whole body visual perceptual-motor skill, but these
different patterns are used to achieve a similar outcome, which
is known as motor equivalence.
Keywords: Individual differences . Visual perceptual-motor
skill . Motor equivalence . Striking sports
Players are the targeted end-users and beneficiaries of exercise-training programmes implemented during coach-led training sessions, and the success of programmes depends upon their active participation. Two variants of an exercise-training programme were incorporated into the regular training schedules of 40 community Australian Football teams, over two seasons. One variant replicated common training practices, while the second was an evidence-based programme to alter biomechanical and neuromuscular factors related to risk of knee injuries. This paper describes the structure of the implemented programmes and compares players' end-of-season views about the programme variants.
METHODS:
This study was nested within a larger group-clustered randomised controlled trial of the effectiveness of two exercise-training programmes (control and neuromuscular control (NMC)) for preventing knee injuries. A post-season self-report survey, derived from Health Belief Model constructs, included questions to obtain players' views about the benefits and physical challenges of the programme in which they participated.
RESULTS:
Compared with control players, those who participated in the NMC programme found it to be less physically challenging but more enjoyable and potentially of more benefit. Suggestions from players about potential improvements to the training programme and its future implementation included reducing duration, increasing range of drills/exercises and promoting its injury prevention and other benefits to players.
CONCLUSIONS:
Players provide valuable feedback about the content and focus of implemented exercise-training programmes, that will directly inform the delivery of similar, or more successful, programmes in the future.
Methods: Eighty-two participants with medial APM and 38 healthy controls were assessed at baseline, with 66 (79%) and 23 (61%) respectively retested at follow-up. Outcome measures included isokinetic knee muscle strength and medial knee joint load inferred through indices of the KAM during normal and fast pace walking.
Results: Knee muscle strength was reduced by 14-16% in the APM leg compared to controls at baseline (p<=0.006). However, strength increased in the APM leg over the 2 years such that there were no differences compared with controls at follow-up. KAM impulse was at least 20% higher for the APM group (both legs) when compared to controls at baseline, and remained similarly higher 2 years later (p<=0.022). At baseline peak KAM was 18% higher in the APM leg as compared to controls only during fast pace walking (p=0.013). The peak KAM increased over the 2 years in the APM leg by 8-9% (p<=0.032), although there were no differences in change in KAM between the APM leg and controls.
Conclusion: This study found that while knee muscle strength improved, dynamic medial joint load increased over the 2-years following APM surgery. These findings may aid in developing therapeutic interventions aimed to prevent or delay the onset of knee osteoarthritis following APM.
Design: Case control study
Methods: Physical activity intensity, number of steps, and minutes spent in activity were objectively quantified using an accelerometer-based activity monitor worn for 7 days. The Knee Injury and Osteoarthritis Outcome Score (KOOS) and concentric quadriceps strength were used to evaluate function post-surgery. Differences in activity levels and functional outcomes between the APM and control participants were assessed using t-tests, while multiple linear regression was used to quantify the best predictors of physical activity.
Results: APM patients engaged in a similar duration of activity to controls (469.0 (128.39) minutes vs. 497.1 (109.9) minutes), and take a similar number of steps per day (9227 (2977) vs. 10383 (3501), but performed their activity at lower levels of intensity than controls. Time spent in moderate (r2 = 0.19) and hard (r2 =0.145) intensity physical activity was best predicted by the Symptoms sub-scale of the KOOS for both controls and APM patients.
Conclusions: APM patients participate in similar activity however at a lower level, with the reduction in activity at higher intensities related to the presence of symptoms of knee osteoarthritis.
Methods: For this cross-sectional study, 122 patients aged 30-55 years, without evidence of knee osteoarthritis at arthroscopic partial medial meniscectomy, underwent gait analysis and MRI on the operated knee once for each sub-cohort of 3 months, 2 years, or 4 years post-surgery. Cartilage volume, cartilage defects, and bone size were assessed from the MRI using validated methods. The 1st peak in the knee adduction moment, knee adduction moment impulse, 1st peak in the knee flexion moment, knee extension range of motion, and the heel strike transient from the vertical ground reaction force trace were identified from the gait data.
Results: Increased knee stance phase range of motion was associated with decreased patella cartilage volume (B = -17.9 (95% CI-35.4, -0.4) p =0.045) while knee adduction moment impulse was associated with increased medial tibial plateau area (B = 7.7 (95% 0.9, 13.3) p = 0.025). A number of other variables approached significance.
Conclusions: Knee joint biomechanics exhibited by persons who had undergone arthroscopic partial meniscectomy gait may go some way to explaining the morphological degeneration observed at the patellofemoral and tibiofemoral compartments of the knee as patients progress from surgery.
Level of Evidence: III
Methodology Eight amateur-level AF clubs (n=1,001 males) volunteered to participate in either 28 weeks of BTT or a ‘sham’ training (ST) adjunct to their normal preseason and regular training. A subset of 34 athletes (BTT, n=20; ST, n=14) were recruited for biomechanical testing in weeks 1–7 and 18–25 of the 28-week training intervention. During biomechanical testing, participants completed a series running, preplanned (PpSS) and unplanned sidestepping (UnSS) tasks. A linear mixed model (α=0.05) was used to determine if knee kinematics and peak moments during PpSS and UnSS were influenced by BTT and/or a season of AF.
Results Both training groups significantly (p=0.025) decreased their peak internal-rotation knee moments during PpSS, and significantly (p=0.022) increased their peak valgus knee moments during UnSS following their respective training interventions.
Conclusions BTT was not effective in changing an athlete's knee joint biomechanics during sidestepping when conducted in ‘real-world’ training environments. Following normal AF training, the players had different changes to their knee joint biomechanics during both preplanned and unplanned sidestepping. When performing an unplanned sidestepping task in the latter half of a playing season, athletes are at an increased risk of ACL injury. The authors therefore recommend both sidestepping tasks are performed during biomechanical testing when assessing the effectiveness of prophylactic training protocols.
Methods: Twenty-five healthy male team sports athletes performed four variations of a landing task. Full body kinematics were identified at initial contact. Peak flexion, valgus and internal rotation moments at the knee, measured during early landing, were normalized to mass and height and statistically compared. Intra-participant correlations were performed between all kinematics and each moment. Mean slopes for each correlation were used to identify the existence of relationships between full body kinematics and knee joint moments.
Findings: Landing after an overhead catch when the ball moved towards a player’s support leg resulted in increased peak valgus moments. These increased valgus moments were correlated with increased knee flexion, hip flexion, and torso lean, as well as torso rotation towards the support leg, and foot and knee external rotation. Increased internal rotation moments were correlated with reduced hip abduction and external rotation, increased ankle inversion, knee external rotation and torso lean away from the support leg.
Interpretation: Learning to land with techniques that do not reflect postures associated with high knee moments may reduce an athlete’s risk of non-contact anterior cruciate ligament injury.
Methods: For this cross-sectional study, 158 patients aged 30-55 years, without evidence of knee osteoarthritis at arthroscopic partial medial meniscectomy (APMM), and 38 controls were recruited. MRI was performed once on the operated knee for each subcohort of 3 months, 2 years, or 4 years post-surgery, and the randomly assigned knee of the controls. Cartilage volume, cartilage defects, and bone size were assessed using validated methods.
Results: Compared with controls, APMM patients had more prevalent cartilage defects in medial tibiofemoral (OR=3.17, 95%CI 1.24-8.11) and patellofemoral (OR=13.76, 95%CI 1.52-124.80) compartments, and increased medial tibial plateau bone area (B=143.8, 95%CI 57.4-230.2). Time from APMM was positively associated with cartilage defect prevalence in medial tibiofemoral (OR=1.02, 95%CI 1.00-1.03) and patellofemoral (OR=1.04, 95%CI 1.01-1.07) compartments, and medial tibial plateau area (B=2.5, 95%CI 0.8-4.3), but negatively associated with lateral tibial cartilage volume (B=-4.9, 95%CI -8.4 to -1.5). The association of APMM and time from APMM with patellar cartilage defects was independent of tibial cartilage volume.
Conclusions: Partial medial meniscectomy is associated with adverse effects on articular cartilage and subchondral bone, which are associated with subsequent osteoarthritis, in both tibiofemoral and patellofemoral compartments.
METHODS:: A kinematic and inverse dynamics model was used to determine ankle and knee joint motion and loading in 22 healthy male participants undertaking running and sidestepping tasks. Both tasks were randomized to planned and unplanned conditions, and undertaken with and without the use of ankle tape.
RESULTS:: At the knee, internal rotation moments (p=<0.001) and varus moments (p<0.05) were reduced for all tasks. Internal rotation impulse (p<0.001) was reduced for sidestepping tasks. Varus impulse during unplanned sidestepping maneuvers (p=0.04) was reduced with the use of ankle tape. However there was a trend toward increased valgus moments and impulse for planned sidestepping trials undertaken with ankle tape (p=0.056). Taping reduced the range of motion at the ankle in all three planes (p<0.05). Peak inversion (p<0.001) was reduced for running trials only. Average eversion and peak dorsiflexion moments were significantly reduced in sidestepping tasks by use of taping.
CONCLUSION:: By limiting motion at the ankle, taping increased mechanical stability at this joint. Ankle taping also provided protective benefits to the knee via reduced internal rotation moments and varus impulses during both planned and unplanned maneuvers. Medial collateral and anterior cruciate ligament injuries may, however, occur through increased valgus impulse during sidestepping undertaken with ankle tape.
Hypothesis: Whole body technique modification would reduce knee loading.
Study Design: Controlled laboratory study.
Methods: Experienced team sport athletes were recruited for whole body sidestep cutting technique modification. Before and
after a 6-week technique modification training, participants performed sidestep cutting tasks while ground-reaction force and motion data were collected. A kinematic and inverse dynamics model was used to calculate 3-dimensional knee loading during sidestep cutting.
Results: At initial foot contact, the participants placed their stance foot closer to the body’s midline and held their torso more upright, in line with the aims of the technique modification training. This was accompanied by significantly lower peak valgus moments in the weight acceptance phase of stance. Both postural changes were correlated with the change in peak valgus moment.
Conclusion: Whole body sidestep cutting technique modification resulted in reduced knee loading.
Clinical Relevance: Implementation of whole body technique modification may produce effective ACL injury prevention programs in sports involving sidestep cutting.