Browsing by Author "Grobler, Lara"

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    Characterisation of running specific prostheses and its effect on sprinting performance
    (Stellenbosch : Stellenbosch University, 2015-12) Grobler, Lara; Terblanche, Elmarie; Ferreira, Suzanne; Stellenbosch University. Faculty of Education. Dept. of Sport Science.
    ENGLISH ABSTRACT: The development of the running specific prosthetic (RSP) has allowed athletes with lower limb amputations to participate at a high level in sports such as sprinting. Literature regarding mechanical properties of RSPs and their influence on the athlete’s performance, on the other hand, is limited. This makes prosthetic selection a difficult task. The aim of this study was to assess the biomechanical and physiological effects of the mechanical characteristics of different RSPs on an athlete’s sprinting performance. The sprint performances of athletes with lower limb amputations were described in a retrospective analysis of Olympic and Paralympic times between 1992 and 2012, in an attempt to assess whether the technological advances in RSPs is evident. A 14 – 26% performance improvement was found for the T42 and T44 classes of the 100 and 200 m during this time in comparison to 2.2 – 2.8% for the Olympic athlete performances. These results were further supported by the lower competition density found in the amputee groups (Olympic 23.90 and 9.29 competitors.s-1; T42 4.53 and 1.93 competitors.s-1). It was therefore proposed that technology played a significant role in the performance progression of these athletes over the last 20 years. Differences in the characteristics of two RSP models (model E and X) were investigated. This was achieved by athlete independent mechanical testing during which the RSPs were dropped from a height of 30 cm and left to bounce on a force platform. The results revealed differences in the peak ground reaction force (GRFpeak) (model E > model X; p < 0.05) and maximal RSP compression (ΔL) (model X > model E; p < 0.05). This indicated that the RSP model E is more stiffness than the model X. These stiffness characteristics related to discrepancies in sprinting economy of an athlete completing four maximal anaerobic running tests (MART) using different RSPs. Two RSP stiffness categories of each model (Ecat4, Ecat6, Xcat4, Xcat6) were used for this testing and was randomly allocated to each testing session. It was found that the running speed at which the athlete attained a blood lactate concentration of 10 mmol.l-1 was the highest with the stiffest RSP (Ecat6), whereas it was the lowest in the softest RSP (Xcat4). Accordingly the lowest functional muscular fatigue as measured by a decrease in the pre and post-test counter movement jump height was found in this condition (Ecat6 7.35% vs. Xcat4 24.43%). From these investigations it was clear that technology is an important factor in the performances of amputee sprint athletes. Therefore prosthetic selection is of the utmost importance. Differences in the mechanical characteristics of the RSPs influence the sprint physiology and biomechanics and should therefore be taken into consideration when selecting a RSP.
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    The effect of graduated compression socks on calf muscle oxygenation of endurance athletes
    (Stellenbosch : Stellenbosch University, 2012-12) Grobler, Lara; Terblanche, E.; Welman, K. E.; Stellenbosch University. Faculty of Education. Dept. of Sport Science.
    ENGLISH ABSTRACT: Compression socks (CS) are used as an ergogenic aid during and after exercise by many athletes of elite and recreational status. The exact mechanism whereby CS affect performance and postexercise recovery is not yet elucidated. Some research ascribes the beneficial effects to improved lactate removal rates with CS. One hypothesis is that CS improve venous return and thereby remove the lactate from the tissue to other tissues such as the liver, and the second hypothesis is that the CS cause retention of the lactate within the muscle and therefore improve the oxidation of the lactate within the muscle (Berry & McMurray, 1987). The current study endeavoured to test the hypothesis set by Berry and McMurray (1987) by measuring the effect of CS as well as flight socks (FS) on muscle oxygenation during exercise and recovery in endurance trained runners and triathletes. Eleven male endurance trained runners and triathletes (age = 34.8 ± 3.8 years, VO2max = 52.4 ± 7.1 mL.kg-1.min-1) participated in the study. They completed an incremental exercise test to exhaustion to determine their maximal aerobic capacity (VO2max) and peak treadmill velocity (PTV). Then they completed two 10 km treadmill running tests at 80 % of their PTV. During these two trials participants wore either CS or FS; the order of treatment was randomly selected. A subset of the study sample (n = 5) also completed a control test wearing only their ankle length sport socks (NS). After these trials, participants completed a 60 minute passive recovery period in the seated position while muscle oxygenation was measured. Compression under the socks was measured at several anatomically determined measurement points prior to the commencement of the exercise test, along with the determination of blood haemoglobin concentration ([Hb]). During the exercise trials, blood lactate concentration ([BLa]), skin temperature (ST),oxygen consumption (VO2), carbon dioxide production (VCO2), heart rate (HR), and muscle oxygenation variables (oxy-haemoglobin (O2Hb), deoxy-haemoglobin (HHb), tissue oxygenation index (TOI) and total haemoglobin index (nTHI)) was measured . During the 60minute passive recovery period, [BLa], ST, O2Hb, HHb, TOI, and nTHI measurements were continued. The results showed that there were differences in the pressure exerted between the two pressure condition (CS and FS) at the posterior ankle, and under the elastic of the sock as well as on the anterior calf at the level of greatest calf circumference. Differences in ST between the CS and NS and the FS and NS conditions were found between the first four 2 km intervals of the exercise protocol, but not during recovery. No differences were found in [BLa] between the three different compression conditions during either the exercise (p = 0.19) or recovery period (p = 0.63), as well as no differences in the cardiorespiratory variables during exercise between the three different compression conditions (VO2, p = 0.06; VCO2, p = 0.12; HR, p = 0.36). With regard to the muscle oxygenation variables, no differences were found between the three compression conditions during exercise, however there was a trend for lower oxygen utilization (HHb) during exercise in the NS condition (p = 0.57, medium to large practical significance). There were also no differences in these variables (O2Hb, p = 0.65; HHb, p = 0.57; TOI, p = 0.39; nTHI, p = 0.22) during recovery, although oxygen utilization (HHb) showed a faster recovery rate with increasing external pressure. From the results obtained, it seems that external compression caused a decrease in the blood flow velocity within the muscle, thereby increasing oxygen diffusion rate. During exercise this did not facilitate differences in [BLa], however, after the first 10 minutes of the recovery period, large practical differences were found between the NS and both sock conditions, suggesting that the increase in oxygen diffusion improved lactate clearance. This could support the hypothesis set by Berry and McMurray (1987).