Physiological and mechanistic characteristics of all-out running using the critical speed concept
- Authors: Kramer, Mark
- Date: 2019
- Subjects: Aerobic exercises , Physical fitness Running Exercise
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/40511 , vital:36178
- Description: The studies described in this thesis, as far as could be ascertained, were the first to investigate the physiological and mechanistic characteristics of all-out running using the critical speed concept specifically applied to field-sport athletes. In the first study the oxygen uptake (𝑉̇𝑂2) kinetics of linear and shuttle all-out running were investigated. The 𝑉̇𝑂2 kinetic parameters were also related to parameters derived from a graded exercise test. No differences were observed in all 𝑉̇ 𝑂2 kinetic parameters between all-out linear and shuttle running, even though differences in all-out testing parameters were evident. The study was novel in that it was, as far as could be ascertained, the first to implement and investigate differences in 𝑉̇𝑂2 kinetics applied to all-out running. The second study investigated whether the parameters derived from all-out linear and shuttle running were representative of aerobic fitness, and the extent to which the all-out test (AOT) related to already established evaluations of aerobic fitness (e.g., graded exercise test [GXT] and the Yo-Yo intermittent recovery test [YYIR1]). It was also investigated whether the parameters from the AOTs could be used to predict the time to completion (tLIM) of shuttle-based performances. The outcomes of this study showed that both the linear and 50-m AOTs were indeed valid for the aerobic assessment of fitness by showing high correlations with maximal pulmonary oxygen uptake (𝑉̇𝑂2𝑚𝑎𝑥). Both the linear and 50-m AOT could therefore be used as surrogates for the evaluation of aerobic fitness. Interestingly, in terms of the tLIM prediction, the 25-m AOT showed the greatest utility. This study was novel on several fronts in that it was the first to: (1) investigate the physiological link between linear and shuttle AOTs and the GXT, (2) investigate the difference between AOTs and the YYIR1, and (3) investigate the application of the AOT methodology to field-based athletes such as rugby players. The third study investigated the energetic cost (EC) of locomotion as well as the metabolic power (𝑃̇) required to run at given speeds. The energetic approach provides a more robust evaluation of the differences between linear and shuttle running due to the all-out nature of the tests. Conventional methods of energy assessment often fall short due to the preclusion of a physiological steady-state, hence requiring more robust mathematical models to evaluate all-out running performance. The results of this study showed that differences between linear and shuttle AOTs are more likely neuromuscular as opposed to physiological. Peak EC and 𝑃̇ were significantly greater for shuttle running compared to linear running, showing clear non-linear increases with each successive increase in running speed. However, the mean EC and 𝑃̇ were not different, showing that all-out shuttle running ‘balances’ the lower running speeds (implying a lower physiological load compared to linear running) with the higher metabolic load imposed by the intense directional changes. This study was novel as it was, as far as could be ascertained, the first to apply the energetic approach to all-out running as well as investigate the differences in energetics between linear and shuttle AOTs. The fourth study provided a means by which the speed-time characteristics of all-out running could be objectively quantified. A novel bi-exponential model was applied to both the linear and shuttle speed-time curves and allowed various mechanistic aspects of the speed-time curve to be characterized. Conventional assessment of the AOT allows for the derivation of only two key parameters, namely critical speed (CS) and the finite distance achievable at speeds exceeding CS (D’). The application of the bi-exponential model expands the number of useful parameters that can be derived from an AOT to seven. The additional useful parameters include: maximum speed [𝑆𝑚𝑎𝑥], time to maximum speed [𝑡𝑐], amplitude of the difference between 𝑆𝑚𝑎𝑥 and CS [𝐴𝑑], curvature constant of the exponential decay [𝜏𝑑] and the asymptote of the exponential decay function [𝑆0], fatigue index showing the percent decline between 𝑆𝑚𝑎𝑥 and CS [FI%], and the finite capacity for running at speeds exceeding CS [D’; representing the area under the curve that is above CS]. The CS and D’ parameters derived from the bi-exponential model were not different to the CS and D’ parameters derived using the conventional method of analysis, thereby showing that the bi-exponential model is a valid means of assessing the curvature characteristics of the AOT, as well as providing additional information that cannot be gleaned from the traditional approach.
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- Date Issued: 2019
Plantar pressure and impulse profiles of students from a South African university
- Authors: Kramer, Mark
- Date: 2012
- Subjects: Human mechanics , Foot -- Movements , Joints -- ange of motion , eng
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:10095 , http://hdl.handle.net/10948/d1010606 , Human mechanics , Foot -- Movements , Joints -- ange of motion
- Description: Most activities of daily living and numerous modes of physical activity incorporate some form of ambulation, of which the foot and ankle constitute the first link in the kinetic chain. A change in foot or ankle structure may therefore have subsequent effects on the superincumbent joints of the human body such as the knee, hip and lower back. Plantar pressure and impulse measurements can therefore provide greater insight into the mechanics of the foot under load-bearing conditions with regards to the areas and regions of the foot that exhibit the largest pressure values and impulse figures. Hence, it is of importance to establish normative data so as to obtain a frame of reference to identify those individuals that fall outside these norms and may exhibit a larger probability of injury. Aim and Objectives: The primary aim was to identify and compare the plantar pressure distribution patterns and impulse values of students of a South African university of different gender and race groups. To realise this aim two specific objectives were set. The first was to determine whether height, weight, body mass index (BMI), gender, race, and the level of physical activity were related to the pressure and impulse values obtained, and the second was to generate reference tables from the normative data gathered. Method: The RS Footscan system was used to measure the pressure and impulse values of the foot. The characteristics that were analysed were height, weight, body mass index and the level of physical activity of the participant and their respective association with plantar pressure and impulse values obtained. This information was then used to establish normative data. A quasi-experimental study design utilising convenience sampling was implemented as the intention was to investigate as single instance in as natural a manner as possible. Convenience sampling was used with predefined inclusion and exclusion criteria. A total of 180 participants were utilised in this study and were subdivided as follows: Gender: Males (n = 90); Females (n = 90); Race: African black (n = 60); white (n = 60) and coloured (n = 60). Each race group therefore comprised of 30 males and 30 females respectively. The anthropometric profile of participants was as follows: Age (S.D.) = 22.21 (S.D. ± 2.93) years; Height (S.D.) = 169.69 (S.D. ± 8.91) cm; Weight (S.D.) = 66.97 (S.D. ± 12.01) kg; BMI (S.D.) = 23.16 (S.D. ± 3.15) kg/m2. Participants were asked to complete a questionnaire prior to testing that would identify all exclusion criteria consisting of: the presence of foot pain or deformity, acute lower extremity trauma, lower extremity surgery, exhibited problems of performance including eye, ear or cognitive impairment, diabetes mellitus or other neurological neuropathy, or the use of walking aids. Anthropometric measurements were then taken for those participants that qualified for the study. Participants were required to perform approximately five warm-up trials to familiarise themselves with the testing equipment before testing commenced. A total of ten successful trails were subsequently recorded for each participant, with three footprints being recorded per trial on the pressure platform, thereby comprising 30 footprints (15 left foot and 15 right foot) per participant that were analysed regarding pressure and impulse values. The two-step gait initiation protocol was implemented which was proven to be a valid and reliable means of assessing gait. Participants were instructed to walk at a comfortable walking speed between 1.19 – 1.60 m/s to ensure conformity between all participants as between-trial gait velocities were proven to be significantly variable. The foot was subdivided into ten anatomical areas focusing on the great toe, lesser toes, metatarsal 1, metatarsal 2, metatarsal 3, metatarsal 4, metatarsal 5, midfoot, medial heel and lateral heel. These ten areas were then grouped into one of three regions, namely the forefoot region (great toe, lesser toes, and all five metatarsal head areas), midfoot region (midfoot area), and rearfoot/heel region (medial and lateral heel areas). Once all relevant data was gathered, corrected and analysed it was used to establish normative data tables pertaining to the various gender and race groups. Results: Of the ten individual pressure and impulse areas, the second and third metatarsal heads demonstrated the highest mean peak pressure and impulse values. Once grouped into one of the three regions, the heel region was ascribed with the largest impulse and pressure values. It was established that statistically and practically significant racial pressure differences were apparent in the left and right forefoot and midfoot regions, with black and coloured individuals yielding the highest values, whereas white participants yielded the lowest. The same was true with regards to impulse figures in that both statistical and practical significant levels were established in the forefoot and midfoot regions. Black and coloured participants exhibited larger impulse values than the white participants. The level of physical activity was found to be associated with both pressure and impulse values over the various regions of the foot. Black individuals that were largely inactive as well as moderately active coloured participants yielded the highest pressure and impulse values, which were found to be statistically and practically significant over the forefoot regions. Conversely, white participants of all physical activity levels as well as coloured participants of both low and high physical activity levels exhibited the lowest pressure values over the forefoot region, which were also found to be statistically and practically significant. The anthropometric variables of height, weight and BMI were found to relate statistically to pressure and impulse values under the various regions of the foot, but none were found to be of any practical significance (r < .30). Conclusion: It was clearly established that both gender and race specific differences existed regarding plantar pressure and impulse values of the normal foot. Plantar pressure and impulse values were also associated with the level of physical activity of the individual, thereby indicating that the level of physical activity could be a contributing factor to altered pressure and impulse values. Anthropometric variables such as height, weight and BMI could not solely account for the variances observed in pressure and impulse. Further research is required to determine whether pressure or impulse values above or below those obtained predispose an individual to injury and to contrast between various activity or sporting codes and the effect of these on plantar pressure and impulse figures. Finally, from the collected data one was able to establish reference tables for the specific gender and race groups for both plantar pressure and impulse values. This enables one to classify individuals based on the pressure and impulse values generated.
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- Date Issued: 2012