Browsing by Author "Swart, Jeroen"
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- ItemOpen AccessA wait-list controlled evaluation of the Qhubeka bicycle on an adolescent's physiology, executive function, and school performance(2021) Mcdonald, Reece Brian; Swart, Jeroen; Holliday, WendyLearner mobility and active school travel (AST) has been proposed to improve school attendance and academic performance. In South Africa, approximately 86% of learners have been reported as walking to and from school. AST in Africa is becoming less common in urban areas, and this may be a contributing factor to the increased risk and frequency of noncommunicable diseases due to decreased physical activity. The aim of this wait-list controlled evaluation was to assess the physiological and cognitive changes of access to a bicycle versus walking on adolescents. Specifically, changes adolescent's physical activity levels and executive function in a South African low-income community. Two schools were recruited, with the evaluation school receiving bicycles and the control a school who were yet to receive bicycles. Significant differences were observed across the physiological and executive function assessments. Most notably in the executive function tests, the evaluation group showed significant time to completion decreases across all three tests (N-Back, Arrow Flanker, WCST: p< 0.001). The results from this study are significant, as they are the first to assess anthropometric, physiological and executive function in South African adolescents from low-socioeconomic regions. It is evident that there are potential improvements in working memory, inhibition and shifting due to cycling as a mode of AST or during leisuretime. Further research needs to determine the specific mechanisms associated with these improvements.
- ItemOpen AccessThe effect of alterations in effective seat tube angle on cycling performance, economy and muscle recruitment(2018) Chye, Teo Choon; Swart, JeroenIntroduction: The bicycle seat tube angle (STA) has been used in scientific research to investigate cycling performance since the early 1980's and has led to inconclusive findings when manipulated between 69° and 82° STA configuration. Most of these studies did not clearly indicate the handlebar positioning in relation to the change in STAs. In addition, the studied duration and intensity were not a true reflection for cycling performance during races. Aim: The study aimed to compare the effect of independent alteration of effective seat tube angle (ESTA) on gross muscle activities, body kinematics and gross economy for well-trained cyclists. Methods: Ten well-trained male cyclists (mean ± SD; age 37.8 ± 3.6 years, height 178.2 ± 3.8 cm, body mass 76.9 ± 8.0 kg, VO₂ₘₐₓ 51.6 ± 5.3 ml/kg/min with 6.8 ± 2.6 years cycling experience and an average training load of 5.8 ± 2.3 hours per week for three months prior) were volunteered for this study. All cyclists were randomly assigned to either a forward or rearward saddle position after an initial preferred saddle cycling position. Each cycling position was performed at 60% of Wₚₑₐₖ for one hour with forty reflective markers placed on bony landmarks described by Vicon full body model Plug-in gait and EMG electrodes placed on the right lower limb on seven muscles. Results: The mean power output and cadences during one hour submaximal steady state cycling differed by a maximum of 0.7W and 3.5 repetitions per minute respectively between three trials. VO₂ values (P=0.95), respiratory exchange ratio (P=0.39) and heart rate (P=0.92) for the trials were not significantly different. Mean angles for each joint and gross muscle activation patterns across the three trials were not significantly different. Magnitude-based inferences statistics showed "possible beneficial effects" on knee and ankle joint kinematics when comparing the forward and rearward saddle displacement. A progressive increase in integrated EMG values was observed for gluteus maximus, biceps femoris and rectus femoris from forward to rearward position. Both vastus lateralis and vastus medialis decreased activation in forward and rearward positions as compared to preferred position. However, none of these changes were statistically significant. Conclusion: Preserving the joint kinematics of the elbow, shoulder, hip, knee and ankle joint of the cyclist when changing the saddle displacement effectively negate any change in heart rate, oxygen consumption and respiratory exchange ratio. Nonetheless, the knee and ankle joints were increased by 1° and decreased by 1.5° respectively when saddle was moved forward. Similar knee and ankle joints effects were also detected with when saddle was moved rearward, which were decreased by 3° and increased by 2° respectively. Therefore, dynamic joint angles should be controlled for future studies when manipulating saddle displacement during cycling. The seven lower limb muscles activations were not statistically significant different when using traditional statistical methods and magnitude type statistic also indicates most unlikely or very unlikely benefits for all surface EMG variables between saddle displacements. These could be due to the high degrees of variability in EMG signal during cycling. Therefore, greater numbers of participants are encouraged for future studies aimed at understanding the coordination of agonist and antagonist muscles at different ESTA. Key words: Effective seat tube angle, submaximal cycling, 3D joint kinematics, electromyography (EMG).
- ItemOpen AccessInteractions between training load, submaximal heart rate, and performance in endurance runners(2019) Johansson, Rebecca Elin; Lambert, Michael; Swart, JeroenBackground: The popularity of endurance running events has rapidly increased in recent years with more recreational runners entering the field. How recreational runners train is not well known. Understanding this and the relationship between training and performance in this group of runners is important for prescribing appropriate training to maximise performance and decrease the risk of injury. This forms the underlying theme throughout this thesis. Aim: The broad aims of this thesis were to better understand the ad libitum training habits of well-trained competitive recreational runners and to determine the relationships between performance, training load, and submaximal heart rate (HR) in this cohort. Methods: Five inter-related studies were performed to: 1) determine relationships between 56-km race performance and pacing (n = 7,327) in competitive recreational runners; 2) determine relationships between 56-km race performance, pacing, and training load in competitive recreational runners (n = 69); 3) determine the accuracy of GPS sport watches in measuring distance (n = 255); 4) develop a feasible and reliable submaximal running test, and 5) determine relationships between performance on a submaximal running test, training load, and submaximal HR in well-trained competitive recreational runners (n = 29). Main findings: A group of well-trained competitive recreational runners performed 44 ± 22 km/week (median ± IQR) in a six-month time frame while training ad libitum. This group had a wide range of inter-individual differences in training load performed even when considering participants who had the same relative marathon performance. The same group of well-trained competitive recreational runners maintained most of their training over a sixmonth period in a range of 0.81 – 1.14 for the acute: chronic workload ratio (ACWR). When the ACWR values reached > 1.50, it was mainly due to participation in endurance running races (> 21-km). When looking at relative weekly changes in training load, the maximum increase was 30% with only two participants having maximum increases of < 10%. The increases in load were predominantly short term (one to two weeks). Submaximal HR had a negative linear relationship with performance in 21% of the study participants. In those participants, poor performances were associated with a higher submaximal HR. Training load was only related to changes in performance in one participant. Conclusion: This thesis confirms that no single variable can provide the necessary information on how to adjust training load to maximise performance. Athletes, coaches, and sports scientists need to have a holistic view of stress exposure and how this affects the body. Although we can only speculate, when the participants had a poor performance it may have been due to factors such as lack of motivation, fatigue, mental stress, dehydration, and/or sleep deprivation. It is important for runners, coaches, and sports scientists to approach the training load – recovery balance as being unique for each athlete. Even in a homogenous group of well-trained competitive recreational runners, their ad libitum training load is widely varied and was not associated with performance or ability level. The balance should be adjusted over time based on the athlete’s symptoms.
- ItemOpen AccessInternal and external load measures as predictors of overuse injury risk in professional football players(2018) Varekamp, Charlene Ghislaine; Swart, JeroenBackground Football is the most popular sport worldwide. Football has grown into a faster, intensive and more competitive game with a substantial increase in technical and physical demands. To reach the peak demands of match play, extensive training is necessary to improve performance and to reach the top level in professional football. Inadequate training loads prevent optimal performance adaptions, place the player at higher risk of being underprepared and may increase the risk of overuse injuries. Determining an optimal training load that improves performance and decreases the risk of overuse injuries is important. Therefore, monitoring and understanding individual responses to training loads are necessary. To date there is limited research regarding prediction of risk of overuse injuries with respect to optimal TL in professional football players. Aim To describe the pattern of injuries and determine the influence of load metrics and injury risk in South African professional football. The total GPS distance covered, the number of GPS measured high-intensity sprints and session Rating Perceived Exertion load and the effects on the risk of developing an overuse injury in professional football players. Objectives (1) To determine the relationship between total GPS distance (m) covered, ACWLR and overuse injuries in a full competitive season. (2) To determine the relationship between GPS measured high-intensity sprints, ACWLR and overuse injuries in a full competitive season. (3) To determine the relationship between session rating of perceived exertion, ACWLR and overuse injuries in a full competitive season. (4) To determine the overuse injury risk per playing position (defenders, midfielders and attackers). (5) To determine the patterns of injury during a full competitive season. (6) To determine the effect of the internal load (sRPE) and external load (GPS) in a congestion week compared to a normal week on overuse injury risk. Methods Data was collected from 32 professional football players in the first and reserve team over one full competitive Premier Soccer League season (2016/17). Training load metrics were assessed using the acute:chronic workload ratio (ACWLR) to predict overuse injury risk within the team. The relationship between total GPS distance (m) covered (TDC), GPS measured high-intensity sprints (HIS), session rating of perceived exertion (sRPE) and ACWLR and overuse injuries was determined. Overuse injuries were described based on frequency, anatomical position and injury type as well as with regards to playing position (defenders, midfielders and attackers). The effect of a congestion week on overuse injury risk was also determined. Results No significant outcomes were recorded when predicting overuse injuries for the whole team, with regards to average TDC, HIS and sRPE ACWLR. Overuse injuries may be predicted when monitoring the individual player loads, thereby taking into account the peak demands of match play per playing position. Large difference between TDC and HIS and large increases or decreases (20%) within weeks may increase the risk of overuse injuries. Hamstrings and groins injuries are the most common injuries sustained and defenders sustained the most overuse injuries within the team relative to exposure time. Congestion weeks did not predict overuse injury risk.
- ItemOpen AccessInternal and external load monitoring in well-trained and professional cyclists(2025) Yila, Rodet-William; Swart, Jeroen; Posthumus, MichaelWith the desire of inducing training adaptations in an athlete to facilitate an increase in performance capacity, as well as develop an increased resilience to fatigue, a sustained period of tolerable physiological stress is required. However, this adaptation is only possible when an adequate period of recovery is afforded to the athlete (Saw et al., 2016). An excessive training induced stress imposed on an athlete, without being afforded an adequate recovery period, may result in an unwanted accumulation of fatigue, which can lead to a decrement in performance, as well an increased likelihood of sustaining an overuse injury or illness (Pyne & Martin, 2011). It should also, however, be noted that when the period of recovery is prolonged, it can also lead to a decrement in performance, as well as increase the likelihood of sustaining an overuse injury as the desirable training adaptations diminish over time in the absence of tolerable physiological stress (Mujika & Padilla, 2000). The purpose of this dissertation was to determine whether the combination of a customised online questionnaire (Subjective Wellness Score, SWS) and a modified submaximal cycling test (Submaximal Fatigue Test, SFT) (internal and external training load monitoring tools) can be used in conjunction with an external training load monitoring tool (TrainingPeaks® Performance Management Chart™, PMC) to monitor the response to training in well-trained and professional cyclists with acceptable validity and reliability. Pre-existing data, already uploaded onto two online registries, was retrospectively analysed. Data from 258 SFTs were analysed from 20 well-trained and professional cyclists, whereby objective and subjective data obtained from the SWS, SFT metrics and TrainingPeaks® PMC metrics was acquired from a continuous, longitudinal dataset. The first question formulated for this dissertation investigated whether the combination of the SWS and metrics of the SFT (HRaverage and RPE) are sensitive to changes in training load. The next question was to scrutinize the validity of the collected SWS questions, SFT metrics, and ETL metrics (of the PMC), and determine whether they are able to predict performance outcomes measured by the SFT (W/kg/RPE, RPE, TTE). The results of the linear regression analysis for ‘All Participants' (n = 20) reported the most significant correlation was found for TSB when compared to the SWS and SFT metrics, with statistically significant results for the variables of fatigue rating (R2 = 0.126; p < 0.001), overall feel rating (R2 = 0.026; p = 0.009), and RPE (R2 = 0.051; p < 0.001). The results of the multivariate analysis for TSS (7-day average), CTL, ATL, and TSB, for ‘All Participants' (n = 5 20) indicated that TSB was found to have the strongest correlation with the SWS and SFT metrics (R2 = 0.197; F = 7.86; p < 0.001). The most significant correlations were found for TSB when compared to the SWS and SFT metrics, with statistically significant results for the variables of overall-feel rating (F = 12.37; p = 0.001) and fatigue rating (F = 28.11; p < 0.001). The results of the linear regression analysis for ‘All Participants' (n = 20) reported the most significant correlations was found for the relative power output per unit of body mass per unit of RPE (W/kg/RPE) when compared to the SWS, HRaverage (of the SFT), and ETL metrics of the PMC, with statistically significant results for the variables of fatigue rating (R2 = 0.110; p < 0.001), TSB (R2 = 0.065; p < 0.001), composite score rating (R2 = 0.034; p = 0.003), overall feel rating (R2 = 0.032; p = 0.004), and sleep rating (R2 = 0.016; p = 0.038). In the multivariate analysis for the modelling of the performance outcome measures of the SFT (W/kg/RPE, RPE, and TTE), for ‘All Participants' (n = 20), RPE was found to have the strongest correlation with the SWS, HRaverage, and ETL metrics of the PMC (R2 = 0.207; F = 7.43; p < 0.001). The most significant correlations were found for W/kg/RPE when compared to the SWS, HRaverage, and ETL metrics of the PMC, with statistically significant results for the variables of overall-feel rating (F = 11.06; p = 0.001), fatigue rating (F = 18.02; p < 0.001), stress rating (F = 8.23; p = 0.005) sleep rating (F = 4.61; p = 0.033), and TSB (F = 4.48; p = 0.035). Considering the findings in this research study, the two questions formulated for this thesis can be answered, whereby as it can be stated, with confidence, that the SWS and SFT metrics (overall-feel rating and fatigue rating) were sensitive to changes in the ETL metric of the PMC (TSB). It was also found that the SWS, HRaverage, and ETL metrics of the PMC were able to a predict performance outcome measure of the SFT, yielding a correlation with W/kg/RPE. Furthermore, it should also be accepted that the combined use of a customised online questionnaire and a modified submaximal cycling test (SFT) can be used in conjunction with the TrainingPeaks® PMC to monitor the response to training in well-trained and professional cyclists with acceptable validity and reliability. In closing, this study suggests that the concurrent use of the SWS, SFT and PMC is an effective and efficient method for coaches/sports scientist to monitor the cyclist's response to their encountered training load as the blend of subjective and objective training load metrics have been found to be sensitive to changes in fatigue status, with acceptable validity and reliability.
- ItemOpen AccessIntrinsic factors, performance and dynamic kinematics in optimisation of cycling biomechanics(2019) Holliday, Wendy; Swart, Jeroen; Fisher, JuliaKinematic measurements conducted during bike set-ups utilise either static or dynamic measures. There is currently limited data on reliability of static and dynamic measures nor consensus on which is the optimal method. The aim of the study was to assess the difference between static and dynamic measures of the ankle, knee, hip, shoulder and elbow. Nineteen subjects performed three separate trials of a 10min duration at a fixed workload (70% of peak power output). Static measures were taken with a standard goniometer (GM), an inclinometer (IM) and dynamic three dimensional motion capture (3DMC) using an eight camera motion capture system. Static and dynamic joint angles were compared over the three trials to assess repeatability of the measurements and differences between static and dynamic values. There was a positive correlation between GM and IM measures for all joints. Only the knee, shoulder and elbow were positively correlated between GM and 3DMC, and IM and 3DMC. Although all three instruments were reliable, 3D motion analysis utilised different landmarks for most joints and produced different means. Changes in knee flexion angle from static to dynamic are attributable to changes in the positioning of the foot. Controlling for this factor, the differences are negated. It was demonstrated that 3DMC is not interchangeable with GM and IM, and it is recommended that 3DMC develop independent reference values for bicycle configuration.
- ItemOpen AccessInvestigation of the impact of compression garments on endurance running performance and exercise induced muscle damage in the lower leg(2018) Geldenhuys, Alda Grethe; Bosch, Andrew; Swart, JeroenIntroduction: Compression garments utilisation is very popular among runners despite the relative lack of consensus in the literature regarding a beneficial impact. Methods: A randomised controlled experimental study was conducted in healthy, uninjured endurance runners (n=41) participating in the Old Mutual Two Oceans 56km race. The experimental group (n=20) trained for six weeks and participated in the race wearing below knee compression garments while the control group (n=21) did not. Participants were tested on four occasions for various markers of exercise induced muscle damage (EIMD) and running performance. Six weeks prior to the race, ultrasound scans of the medial gastrocnemius, mid-calf and figure-of-8 ankle circumference baseline measurements were performed. Shortly prior to the race, these measurements were repeated in addition to a countermovement jump (CMJ) test. Immediately following the race, circumference measurements and CMJ testing were repeated in addition to pain ratings on the visual analogue scale (VAS). Race performance times were also obtained. Two days following the race, the ultrasound scans, circumference measurements and VAS pain ratings were repeated. Results: Ankle circumferences measurements increased significantly less (p=0.01, Cohen's d=0.9) in the experimental group from immediately after the race until two days post-race compared to the control group. There were no further statistically significant changes over time in any other objective outcome measure (i.e. mean mid-calf circumference, medial gastrocnemius mean muscle thickness and mean pennation angle, mean CMJ height and estimated peak power output nor in race performance) between the experimental and control groups. Selected pain ratings were statistically significantly worse in the experimental group. Muscle thickness and pennation angles were significantly greater in the control group compared to the experimental group two days following the race. Conclusion: There were limited indications of a beneficial impact of compression garments with minor improvements in ankle circumference measurements, but no further significant effects related to EIMD were detected. Furthermore, no ergogenic impact was detected. Based on the results of the study, there is limited evidence to support the continued utilisation of commercially available below knee compression garments during running.
- ItemOpen AccessThe efficacy of high intensity training prescribed using either heart rate or power on performance variables in well trained cyclists(2007) Swart, JeroenUnable to copy and paste abstract from PDF document