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Muller J.H.,Stellenbosch University | Zakaria T.,Tornier | van der Merwe W.,Sports Science Institute of South Africa | D'Angelo F.,University of Insubria
Computer Methods in Biomechanics and Biomedical Engineering | Year: 2015

Anterior–posterior stability in an unconstrained mobile-bearing total knee arthroplasty (TKA) and one with rotational constraints is compared in a computational model based on an ASTM test. Both TKA designs dislocate at loads greater than reported maximum in vivo forces. The posterior drawer forces (mean: 3027 N vs. 1817 N) needed to induce subluxation increase with a greater anterior jump distance (12 mm vs. 7 mm; refers to the vertical height of the anterior or posterior border of the tibial insert's articulating surface). The posterior jump distance for both tested TKA differed by 1.5 mm and had minimal effect on the magnitude of the anterior drawer forces at dislocation in mid-flexion (unconstrained vs. constrained: 445 N vs. 412 N). The unconstrained insert dislocated by means of spin-out whereas in the constrained TKA the femur dislocated from the bearing during posterior drawer and the bearing from the baseplate during anterior drawer. MCL function is an important consideration during ligament balancing since a ± 10% variation in MCL tension affects dislocation forces by ± 20%. The simulation platform provided the means to investigate TKA designs in terms of anterior–posterior stability as a function of knee flexion, collateral ligament function and mechanical morphology. © 2015 Taylor & Francis


Muller J.H.,Stellenbosch University | Zakaria T.,Tornier | Renault E.,Tornier | Van Der Merwe W.,Sports Science Institute of South Africa
9th South African Conference on Computational and Applied Mechanics, SACAM 2014 | Year: 2014

Total knee prostheses are surgically installed to replace articulating surfaces in knee joints. Various designs exist to assist with or facilitate knee function. Their efficacy is traditionally verified through experimental wear tests and clinical follow-up studies, which are expensive in terms of time, patient risk and equipment. A validated musculoskeletal model provides a repeatable test platform on which different designs can be tested. A musculoskeletal model is formulated from a dataset provided for The Grand Challenge to Predict in-vivo Knee Loads to simulate a deep knee squat. The model output is validated against the experimentally measured tibiofemoral reaction force (dataset) in terms of a RMS error and coefficient of correlation. Four prosthesis designs are virtually implanted and analysed throughout a set of parameters. The RMS error and coefficient of correlation (r) for the deep squat exercise is: RMSerror = 384.9 N and r = 0.88 (p<0.05). The RMS error represents 16% of the full scale output, which is acceptable when considering the simplifications that have been made in the formulation of the model.


PubMed | Sports Science Institute of South Africa, Stellenbosch University, University of Insubria and Tornier
Type: Journal Article | Journal: Computer methods in biomechanics and biomedical engineering | Year: 2016

Anterior-posterior stability in an unconstrained mobile-bearing total knee arthroplasty (TKA) and one with rotational constraints is compared in a computational model based on an ASTM test. Both TKA designs dislocate at loads greater than reported maximum in vivo forces. The posterior drawer forces (mean: 3027N vs. 1817N) needed to induce subluxation increase with a greater anterior jump distance (12mm vs. 7mm; refers to the vertical height of the anterior or posterior border of the tibial inserts articulating surface). The posterior jump distance for both tested TKA differed by 1.5mm and had minimal effect on the magnitude of the anterior drawer forces at dislocation in mid-flexion (unconstrained vs. constrained: 445N vs. 412N). The unconstrained insert dislocated by means of spin-out whereas in the constrained TKA the femur dislocated from the bearing during posterior drawer and the bearing from the baseplate during anterior drawer. MCL function is an important consideration during ligament balancing since a 10% variation in MCL tension affects dislocation forces by 20%. The simulation platform provided the means to investigate TKA designs in terms of anterior-posterior stability as a function of knee flexion, collateral ligament function and mechanical morphology.


Lombard W.P.,Sports Science Institute of South Africa | Lombard W.P.,University of Cape Town | Durandt J.J.,Sports Science Institute of South Africa | Masimla H.,South African Rugby Union | And 2 more authors.
Journal of Strength and Conditioning Research | Year: 2015

Lombard, WP, Durandt, JJ, Masimla, H, Green, M, and Lambert, MI. Changes in body size and physical characteristics of South African under-20 rugby union players over a 13-year period. J Strength Cond Res 29(4): 980-988, 2015 - This study compared changes in the body size and physical characteristics of South African under-20 rugby union players over a 13-year period. A total of 453 South African under-20 players (forwards: n 256 and backs: n 197) underwent measurements of body mass, stature, muscular strength, endurance, and 10- and 40-m sprint times. A 2-way analysis of variance was used to determine significant differences for the main effects of position (forwards vs. backs) and time (1998-2010). The pooled data showed that forwards were significantly heavier (22%), taller (5%), and stronger (18%) than the backs. However, when 1 repetition maximum strength scores were adjusted for body mass, backs were stronger per kg body mass. Stature did not change over the 13-year period for both groups. There were, however, significant increases in muscular strength (50%), body mass (20%), and muscular endurance (50%). Furthermore, an improvement in sprint times over 40 (4%) and 10 m (7%) was evident over the period of the study. In conclusion, the players became heavier, stronger, taller, and improved their upper-body muscular endurance over the 13 years of the study. Furthermore, sprint times over 10 and 40 m improved over the same time period despite the increase in body mass. It can be speculated that the changes in physical characteristics of the players over time are possibly a consequence of (a) adaptations to the changing demands of the game and (b) advancements in training methods. © 2015 National Strength and Conditioning Association.


Steyn N.P.,University of Cape Town | De Villiers A.,Non communicable Diseases Research Unit | Gwebushe N.,Biostatistics Unit | Draper C.E.,University of Cape Town | And 6 more authors.
BMC Public Health | Year: 2015

Background: Numerous studies in schools in the Western Cape Province, South Africa have shown that children have an unhealthy diet with poor diversity and which is high in sugar and fat. HealthKick (HK) was a three-year randomised controlled trial aimed at promoting healthy eating habits. Methods: Sixteen schools were selected from two low-income school districts and randomly allocated to intervention (n = 8) or control school (n = 8) status. The HK intervention comprised numerous activities to improve the school nutrition environment such as making healthier food choices available and providing nutrition education support. Dietary intake was measured by using a 24-h recall in 2009 in 500 grade 4 learners at intervention schools and 498 at control schools, and repeated in 2010 and 2011. A dietary diversity score (DDS) was calculated from nine food groups and frequency of snack food consumption was determined. A school level analysis was performed. Results: The mean baseline (2009) DDS was low in both arms 4.55 (SD = 1.29) and 4.54 (1.22) in the intervention and control arms respectively, and 49 % of learners in HK intervention schools had a DDS ≤4 (=low diversity). A small increase in DDS was observed in both arms by 2011: mean score 4.91 (1.17) and 4.83 (1.29) in the intervention and control arms respectively. The estimated DSS intervention effect over the two years was not significant [0.04 (95 % CI: -0.37 to 0.46)]. Food groups least consumed were eggs, fruit and vegetables. The most commonly eaten snacking items in 2009 were table sugar in beverages and/or cereals (80.5 %); followed by potato crisps (53.1 %); non-carbonated beverages (42.9 %); sweets (26.7 %) and sugar-sweetened carbonated beverages (16 %). Unhealthy snack consumption in terms of frequency of snack items consumed did not improve significantly in intervention or control schools. Discussion: The results of the HK intervention were disappointing in terms of improvement in DDS and a decrease in unhealthy snacking. We attribute this to the finding that the intervention model used by the researchers may not have been the ideal one to use in a setting where many children came from low-income homes and educators have to deal with daily problems associated with poverty. Conclusions: The HK intervention did not significantly improve quality of diet of children. © 2015 Steyn et al.


PubMed | Sports Science Institute of South Africa, Biostatistics Unit, BroadReach Healthcare, Non communicable Diseases Research Unit and University of Cape Town
Type: | Journal: BMC public health | Year: 2015

Numerous studies in schools in the Western Cape Province, South Africa have shown that children have an unhealthy diet with poor diversity and which is high in sugar and fat. HealthKick (HK) was a three-year randomised controlled trial aimed at promoting healthy eating habits.Sixteen schools were selected from two low-income school districts and randomly allocated to intervention (n=8) or control school (n=8) status. The HK intervention comprised numerous activities to improve the school nutrition environment such as making healthier food choices available and providing nutrition education support. Dietary intake was measured by using a 24-h recall in 2009 in 500 grade 4 learners at intervention schools and 498 at control schools, and repeated in 2010 and 2011. A dietary diversity score (DDS) was calculated from nine food groups and frequency of snack food consumption was determined. A school level analysis was performed.The mean baseline (2009) DDS was low in both arms 4.55 (SD=1.29) and 4.54 (1.22) in the intervention and control arms respectively, and 49% of learners in HK intervention schools had a DDS 4 (=low diversity). A small increase in DDS was observed in both arms by 2011: mean score 4.91 (1.17) and 4.83 (1.29) in the intervention and control arms respectively. The estimated DSS intervention effect over the two years was not significant [0 .04 (95% CI: -0.37 to 0.46)]. Food groups least consumed were eggs, fruit and vegetables. The most commonly eaten snacking items in 2009 were table sugar in beverages and/or cereals (80.5%); followed by potato crisps (53.1%); non-carbonated beverages (42.9%); sweets (26.7%) and sugar-sweetened carbonated beverages (16%). Unhealthy snack consumption in terms of frequency of snack items consumed did not improve significantly in intervention or control schools.The results of the HK intervention were disappointing in terms of improvement in DDS and a decrease in unhealthy snacking. We attribute this to the finding that the intervention model used by the researchers may not have been the ideal one to use in a setting where many children came from low-income homes and educators have to deal with daily problems associated with poverty.The HK intervention did not significantly improve quality of diet of children.


Testa M.,University of Paris Descartes | Testa M.,Study Group for European Culture and Solidarity | Noakes T.D.,Sports Science Institute of South Africa | Desgorces F.-D.,University of Paris Descartes | Desgorces F.-D.,Institute of Sport Biomedical and Epidemiology Research
Journal of Strength and Conditioning Research | Year: 2012

Training state improves the relationship between rating of perceived exertion and relative exercise volume during resistance exercises. J Strength Cond Res 26(11): 2990-2996, 2012-The aim of this study was to investigate how the rating of perceived exertion (RPE) during resistance exercises was influenced by the exercise volume and athletes' training state. Eighty physical education students (well trained, less well trained, and novices) rated their perceived exertion of multilift sets using the category-ratio scale. These sets were performed with moderate (60-80% of 1-repetition maximum [1RM]) and heavy loads (80-100% of 1RM) involving low volume of exercise (5.5 6 1.1 reps for moderate and 1.3 6 0.4 reps for the heavy load) and high volume of exercise (moderate load: 17.562.1 reps; high load: 2.960.6 reps). The exercise volume of the sets was expressed relatively to individual maximal capacities using the maximum number of repetition (MNR) for the load lifted. General linear model describes that RPE was related to MNR % with a training state effect (p , 0.01) observed only for sets involving a low MNR % and without effect of absolute volume and exercise intensity (high MNR sets: adjusted R2 = 0.65 and 0.78 and low MNR sets adjusted R2 = 0.37 and 0.34 in lowMNR tests). High standard errors of estimated relative volume appeared when using the RPE from low exercise volume sets (12.8 and 14.4% of actual relative volume). Coaches should consider the RPE resulting from high exercise-induced physical strain to estimate the actual relative volume and to estimate the individual MNR at a given load. © 2012 National Strength and Conditioning Association.


Asplund C.A.,U.S. Army | O'Connor F.G.,Uniformed Services University of the Health Sciences | Noakes T.D.,University of Cape Town | Noakes T.D.,Sports Science Institute of South Africa
British Journal of Sports Medicine | Year: 2011

Exercise-associated collapse (EAC) commonly occurs after the completion of endurance running events. EAC is a collapse in conscious athletes who are unable to stand or walk unaided as a result of light headedness, faintness and dizziness or syncope causing a collapse that occurs after completion of an exertional event. Although EAC is perhaps the most common aetiology confronted by the medical provider attending to collapsed athletes in a fi nish-line tent, providers must fi rst maintain vigilance for other potential life-threatening aetiologies that cause collapse, such as cardiac arrest, exertional heat stroke or exercise-associated hyponatraemia. Previously, it has been believed that dehydration and hyperthermia were primary causes of EAC. On review of the evidence, EAC is now believed to be principally the result of transient postural hypotension caused by lower extremity pooling of blood once the athlete stops running and the resultant impairment of cardiac barorefl exes. Once life-threatening aetiologies are ruled out, treatment of EAC is symptomatic and involves oral hydration and a Trendelenburg position - total body cooling, intravenous hydration or advanced therapies is generally not needed.


Marraccini T.,University of Cape Town | Meltzer S.,Sports Science Institute of South Africa | Bourne L.,South African Medical Research Council | Elizabeth Draper C.,University of Cape Town
Childhood Obesity | Year: 2012

Background: Both under- and over-nutrition pose a public health concern, especially for children in South Africa. Several initiatives exist in South Africa directed at promoting healthy eating and nutrition at schools. One of them is the Woolworths Making the Difference (MTD) Programme aimed at eliminating barriers to promoting healthy lifestyles that exist at schools, such as the availability of low-cost, unhealthy foods either from tuck shops (small food shops) or street vendors. The Healthy Tuck Shop Guide is a recent addition to the MTD Programme. The aim of this evaluation was to assess awareness, potential uptake, and perceptions of the Woolworths Healthy Tuck Shop Guide among parents and staff in a sample of schools that were exposed to the guide. Methods: A qualitative study consisting of focus groups, interviews, and tuck shop observation was used to gather information on 13 schools and their exposure, comprehension, and use of the guide. A mix of schools was examined in terms of economic status and level of control over their tuck shop. Thematic analysis was used to extract findings. Results: Findings show that despite overall positive attitudes about the guide several barriers to its implementation exist, including children's preferences for unhealthy foods, the higher cost of healthy foods, and other issues related to a lack of facilities, time and manpower. Conclusion: Findings suggest that the Woolworths Healthy Tuck Shop Guide would contribute more meaningfully to the creation of healthier food environments if executed within a larger support network to address barriers to implementation. © 2012 Mary Ann Liebert, Inc.


In 1991, we provided definitive evidence that exercise-associated hyponatraemia (EAH) is caused by abnormal fluid retention in those who overdrink during prolonged exercise, but this finding was ignored. Instead, in 1996, influential guidelines of the American College of Sports Medicine (ACSM) promoted the concept that athletes should drink 'as much as tolerable' during exercise. What followed was an epidemic of cases of EAH and its associated encephalopathy (EAHE). A recent study funded by the sports drink industry confirms our 1991 finding by showing that 95% of the variance in the serum sodium concentration during exercise can be explained by changes in body mass alone. The possibility is that commercial influence delayed the acceptance of our findings for two decades.

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