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An investigation is made into the flow of fluids through deformable porous materials with the aim of an application to articular cartilage, which depends on interstitial fluid for some of its mechanical properties. The law governing flows due to fluid pressure is shown to be valid in a cylinder of material with the same permeability in all directions, both with axial flow only and with axial and radial flow combined, up to Reynolds numbers of about 1. A literature survey shows that there is a large range of values of Reymolds numbers proposed as the limit of the validity of this law, indicating that there is no universal "critical" Reynolds number inflow through porous media. The variation of permeability with strain is measured, both indirections parallel and perpendicular to the direction of applied strain, inlay porous polymeric material. A model of articular cartilage is proposed which consists of a porous solid matrix, which has a reversible non-linear load/displacement characteristic, with liquid-filled pores. Assuming a simple variation of permeability with strain predicts time-dependent deformations to a good degree of accuracy, agreement being excellent at normal physiological loads. Under oscillating loads, deformations are much larger than those predicted by the model, and it is thought that this is due to the effect of the bulk modulus of the cartilage, which becomes dominant in short term responses.

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Dry-land ergometry has been proposed as an alternative method to water-based testing in an attempt to circumvent the difficulties associated with physiological assessment of swimmers during swimming itself. The aim of the studies presented in this thesis was to evaluate the usefulness of dry-land ergometry. The objectives of the studies presented in this thesis were to ascertain whether dry-land measurements could differentiate between trained and untrained swimmers, assess the effects of training and reflect water-based measurements. To realise this aim and the objectives, three studies that assessed physiological parameters of swimmers using dry-land ergometry and water-based testing were undertaken. The first study compared lactate and oxygen uptake responses to separate dry-land armpulling and leg-kicking in recreational (RSW) and collegiate swimmers (SW). The exercise intensity at a blood lactate concentration of 4 mmol-l" (E~) and the peak oxygen uptake (V OZpeok), peak exercise intensity (ElpeU.)and peak lactate (HLapeU.)responses to incremental arm-pulling and leg-kicking were established for both groups. The results showed that, for armpulling, SW achieved higher E~ (94 ± 6.0 W versus 70 ± 6.3 W; P<0.05) and EIpeok(114 ± 6.0 W versus 90 ± 4.0 W; P<0.05) than RSW, whereas, for leg-kicking, none of the responses differed between the two groups. These results suggested that arm conditioning was enhanced in SW and this was reflected in the dry-land measurements of E4nM and EIpeok. Therefore, it was possible to establish the differences in physiological responses between SW and RSW using dryland ergometry. The second study assessed the effects of arms- versus legs-only swimming training on performance indices and gas exchange responses to separate dry-land arm-pulling and leg-kicking in competitive swimmers. Two groups of swimmers performed arms- (ARMS) or legs-only (LEGS) swimming exercises for 20% of their training time, 3 times a week for six weeks. Waterbased (swim trials) and dry-land assessments were conducted prior to and immediately after the 6-week training period. The swim trials included a 200 m arms-only (200ARMS),a 200 m legs-only (200u,GS) and a 400 m (400ruu) front crawl test. Distance per pull (DPP) and distance per kick (DPK) for 200ARMSand 200LEOS were calculated from video recordings. The dry-land assessments included measurements of oxygen uptake (V02), ventilatory threshold (VT) and total exercise time (TEn during an incremental arm-pulling and leg-kicking exercise test. The results showed that arm training improved 200ARMS(184 ± 10.0 s versus 164 ± 6.0 s) and DPP (+10 ± 3%) in the ARMS and leg training improved 200u,os (223 ± 10.0 versus 211 ± 10.0 s) and DPK (+5 ± 2%) in the LEGS (all at P<0.05). The changes due to arm training were reflected in the armII ulling measurements of increased VTw (+20 ± 3%), reduced V02 at 60W (-18 ± 2%) and increased TET (465 ± 8 s versus 675 ± 15 s), whereas the changes due to leg training were reflected in VT w (+37 ± 5%) and reduced V02 at 60W (-20 ± 3%). These results suggested that arms- or legs-only swimming training induces changes in arms- or legs-only swmunmg performance, but these do not necessarily translate into improved full-stroke swimming performance. Also, results indicate that dry-land ergometry can detect the changes due to armsor legs-only swimming training in the physiological responses to arm-pulling or leg-kicking. The third study compared the cardiopulmonary responses to whole-body, arms- and legsonly dry-land exercise and free swimming. The peak oxygen uptake (V 02pea) and peak heart rate (HR,eu) responses to whole-body, arm-pulling and leg-kicking exercise were established in both exercise modalities. The results showed that V02peak was higher in whole-body exercise than arms-only or legs-only exercise in both exercise modalities (dry-land: 3.69 ± 0.18 l-min" versus 3.18 ± 0.43 lmin" and 3.15 ± 0.54 l-min", respectively. P<0.05, swimming: 4.12 ± 0.84 l-min" versus 3.36 ± 0.52 l-min" and 3.55 ± 0.43 l-min", respectively; P<0.05) and also that whole-body V02peak was 10% higher during free swimming than during dry-land exercise. No differences were noted for HRpea between whole-body, arms-only and legs-only exercise in both exercise modalities. These results suggested that the higher VOZpeak noted for whole-body free swimming compared to combined arm-leg exercise could be due to limitations in the design of the dry-land ergometer used as the difference was small. Therefore, it was shown that dry-land measurements compare favourably with water-based measurements. The use of dry-land ergometry presents several limitations, which are mainly concerned with the design of this equipment. However, all the above fmdings demonstrate that dry-land ergometry might be a valuable tool for assessment of those physiological responses (i.e. continuous measurement of gas exchange measures) that, at present, are difficult to be conducted in the water. Therefore, dry-land ergometry might be used as an alternative and/or supplement to water-based testing.

Bones are a fundamental element of the musculoskeletal system with complex tasks. They need to be lightweight to allow effective locomotion, but also strong enough to resist external forces of often several times body weight. This is possible due to the combination of unique material characteristics and a structure that adjusts to changing requirements. However, bone mass is generally proposed to decrease with age, contributing to an enhanced fracture incidence, which is strongly associated with morbidity, mortality and rising health care costs. The understanding of the bones' adaptation to mechanical forces is vital to preserve good bone health into old age and thus to prevent Osteoporosis the most common skeletal disorder. The objectives of this thesis were to investigate the adaptation of the middle aged and the elderly skeleton to various types of mechanical loading of differing magnitudes, and to evaluate the etiology of the age-related loss of bone mass and strength in the context of strenuous long-term exercise. Altogether 448 participants were involved in the study. The cross-sectional comparisons of bone mass and strength between athletes of differing disciplines and controls showed that differences at the mechanically loaded tibia increased systematically as the discipline specific speed decreased, i.e. greatest differences were found between sprinters and controls amounting to -12% in males and to -20% in females. In the radius no group differences of bone measures were observed, except for sprint cyclists,who had larger bone mass and strength than the controls. Age dependencies considered primarily structural shaft measures of both the radius and the tibia of track and field athletes, whereas fewer correlations were found in either the controls or the cyclists. The correlations appeared to be stronger if the values were larger at young age (40 yrs), i.e. in the tibia of sprint runners. Also, they were stronger and more systematic in females than in males. In co~clusion, mechanical loading was positively associated with bone strength in the middle aged and elderly study participants. The reduction in athletic performance with age may be associated with the observed loss in tibial bone strength in the athletes but not the controls, because maintenance of bone strength 'is dependent on the exposure to mechanical loading in both athletes and non-athletes. The stronger age correlations in the radius compared to the tibia imply a protective effect of exercise against an age related loss in bone mass and strength. Larger athlete vs. control group differences along with stronger age correlations in females as opposed to males suggest a gender specific response to mechanical loading.

The dynamics of everyday activities such as catching or kicking a ball, lifting a cup, crossing a road, or driving a vehicle require the ability to perceive and adjust to circumstances and environments. For interception or object avoidance, effective perception action coupling emerges from one's ability to optimally interpret meaningful visual information relative to self constraints and abilities. With increasing age, there is clear improvement in timing of one's behaviour to coincide with the visual information one perceives (Bard, Fleury, Carriere & Bellec, 1981). It was unclear how adults and children couple perceived information to their own constraints to successfully intercept when faced with increasingly complex tasks (i.e. faster moving objects, and travelling smaller approach angles to the object)-. Recent research in adults depicted the bearing angle (BA) as a key optic variable that allows one to reach the right place at the right time when intercepting a moving object, by maintaining a constant bearing angle (CBA). The present thesis adapted the study of this strategy in order to evaluate its use in a manual interceptive task. It examined the influence of extrinsic factors on the adherence to this strategy in synchronised movement control patterns. In effect the present work aimed td-address the issue of how perception action coupling influences the strategy and movement control (posture and timing) of adults and typically developing children when intercepting a moving object. . The findings of this thesis suggest that on approach for interception the CBA strategy is largely adhered to in adults and older children and not in younger children. This strategy breaks down on reaching, and the wrist compensates for movement requirements relative to ball velocity and approach angle. Larger deviations occurred when the angle of approach was small and for faster balls. Younger children were unable to adhere to the CBA strategy on approach, requiring more information from slower balls and smaller angles of approach, failing to effectively couple walking velocity to ball velocity. However there were signs of a compensatory strategy emerging. Greater postural adjustments were made by all three participant groups when there was less deviation from the CBA strategy and when intercepting faster balls. Adults and older children showed proximodistal control, making greater adjustments in the trunk during reaching. Younger children tended to make less adjustment at the trunk and controlled their reaching behaviour by making more distal adjustments. All participants were able to compensate successfully in their adaptations of posture and use of the CBA strategy, according to their age, ability and experience, to achieve the desired goal of interception. Improvement with age suggests that compliance to theCBA strategy may be attributed to enhanced coincidence anticipation behaviour.