The effects of +Gz force on the bone mineral density of fighter pilots

HYPOTHESIS Bone is a metabolically active tissue which responds to high strain loading. The purpose of this study was to examine the bone response to high +Gz force loading generated during high performance flying. METHODS The bone response to +Gz force loading was monitored in 10 high performance RAAF pilots and 10 gender-, age-, height-, weight-matched control subjects. The pilots were stationed at the RAAF base at Pearce, Western Australia, all completing the 1-yr flight training course. The pilots flew the Pilatus PC-9 aircraft, routinely sustaining between 2.0 and 6.0 +Gz. Bone mineral density (BMD) and bone mineral content (BMC) were measured at baseline and 12 mo, using the Hologic QDR 2000+ bone densitometer. RESULTS After controlling for change in total body weight and fat mass, the pilots experienced a significant increase in BMD and BMC for thoracic spine, pelvis, and total body, in the magnitude of 11.0%, 4.9%, and 3.7%, respectively. However, no significant changes in bone mineral were observed in the pilots lumbar spine, arms or legs. The control group experienced a significant decrease in pelvic BMC, with no other bone mineral changes observed at any site. CONCLUSIONS These findings suggest that site specific BMD is increased in response to high +Gz forces generated during high performance flying in a PC-9.

Prospective decrease in progesterone concentrations in female lightweight rowers during the competition season compared with the off-season: A controlled study examining weight loss and intensive exercise

The purpose of this study was to monitor ovarian hormone function response to intense exercise and body weight changes in female athletes. Ovarian hormone function was evaluated in 12 female lightweight rowers and 10 age-height-weight matched sedentary controls. Ovarian hormone function was assessed during consecutive competition season and off season, by measurement of peak and average alternative day overnight urinary oestrone glucuronide (E1G) and pregnanediol glucuronide (PdG) excretion. Competition season was associated with a 5.8 kg (9.3%) body weight loss in the lightweight rowers. Significantly lower competition season peak and average urinary excretion of PdG were found in the lightweight rowers compared with the controls. Lower competition season peak and average urinary excretion of E1G were also found in the lightweight rowers compared with the controls, but the difference did not reach significance. The number of rowing training hours was a significant determinant of peak PdG excretion in the rowers (R2 = 0.40; p<0.02). The seasonal suppression of PdG excretion was associated with degree of weight loss (R2 = 0.46; p<0.01). The competition related decrease in E1G and PdG excretion for the lightweight rowers was predominantly restored during the off season when exercise intensity and duration were decreased and body weight increased. These results showed a significant (p<0.05) reduction in progesterone metabolite excretion and a non-significant decrease in oestrone metabolite excretion associated with intensive competition season training loads and body weight reduction in female lightweight rowers.

Seasonal variations in the body composition of lightweight rowers

OBJECTIVE To monitor the seasonal body composition alterations in 18 lightweight rowers (six females, 12 males) across a rowing season incorporating preseason, early competition, competition, and postseason. METHODS Subject age was 23.1 (SD 4.5) years, height 170.8 (5.6) cm (female, 23.5 (3.5) years, 180.5 (2.7) cm (male). Body weight, fat mass, and fat-free mass (FFM) were assessed using dual energy x ray absorptiometry (DXA-L Lunar) and skinfold techniques. Weight control techniques were documented before major regattas by a questionnaire. RESULTS Female body weight was reduced from 61.3 (2.9) to 57.0 (1.1) kg (5.9%), while male body weight was reduced from 75.6 (3.1) to 69.8 (1.6) kg (7.8%) preseason to competition season respectively. These body weight reductions were mirrored by a significant reduction in fat mass as indicated by the sum of skinfolds [female seven sites: 80.9 (8.1) to 68.2 (11.8) mm; male eight sites: 54.2 (8.7) to 41.8 (4.8) mm], percentage body fat [female 22.1 (1.0) to 19.7 (2.4)%; male 10.0 (0.9) to 7.8 (0.8)%], and total fat [female 12.5 (5.2) to 10.9 (1.4) kg; male 7.3 (1.9) to 5.6 (1.8) kg] (DXA). In contrast, no changes were observed in FFM despite a season of intensive rowing training. Seasonal body weight control was achieved through reduced total energy and dietary fat intakes. Acute body weight reductions were achieved by exercise in 73.3% of participants, food restriction in 71.4%, and fluid restrictions in 62.9%. CONCLUSIONS Seasonal body weight alterations in lightweight rowers are in response to a significant reduction in fat mass. However, the weight restrictions appear to be limiting an increase in FFM which could be beneficial to rowing performance.

Phenotypic variation in natural populations of kikuyu in Australia

The quality of tropical grasses is a major limitation to animal production in tropical and subtropical areas. This is mainly associated with the lower digestibility because C4 grasses have higher fibre levels. Any improvement in quality would require a reduction in the lignin and an increase in the digestion of the neutral detergent fibre content of these plants (Clark and Wilson 1993). Kikuyu (Pennisetum clandestinum) is an important grass for the dairy and beef industries of the subtropics of Australia, South Africa and New Zealand (Mears 1970). Increased digestibility could substantially improve animal production in these industries. These experiments investigated the variation in agronomic and quality of natural populations selected from diverse regions within Australia. Runners of 14 kikuyu selections were collected by project staff or local agronomists from areas considered to have grown kikuyu for over 30 years while Whittet and Noonan were established by seed. Entries were established as single spaced plants on a 1.5 m grid in a randomised block with 3 replicates and evaluated under irrigation at Mutdapilly (brown podsol) and Wollongbar (red ferrosol). Foliage height, forage production and runner yield were assessed along with crude protein (CP), in vitro dry matter digestibility (IVDMD), metabolisable energy (ME), acid detergent fibre (ADF) and neutral detergent fibre (NDF) content of the leaf in autumn, winter and spring.

Developmental origins of psychological vulnerability factors for mental disorders

Premature birth and associated small body size are known to affect health over the life course. Moreover, compelling evidence suggests that birth size throughout its whole range of variation is inversely associated with risk for cardiovascular disease and type 2 diabetes in subsequent life. To explain these findings, the Developmental Origins of Health and Disease (DOHaD) model has been introduced. Within this framework, restricted physical growth is, to a large extent, considered either a product of harmful environmental influences, such as suboptimal nutrition and alterations in the foetal hormonal milieu, or an adaptive reaction to the environment. Whether inverse associations exist between body size at birth and psychological vulnerability factors for mental disorders is poorly known. Thus, the aim of this thesis was to study in three large prospective cohorts whether prenatal and postnatal physical growth, across the whole range of variation, is associated with subsequent temperament/personality traits and psychological symptoms that are considered vulnerability factors for mental disorders. Weight and length at birth in full term infants showed quadratic associations with the temperamental trait of harm avoidance (Study I). The highest scores were characteristic of the smallest individuals, followed by the heaviest/longest. Linear associations between birth size and psychological outcomes were found such that lower weight and thinness at birth predicted more pronounced trait anxiety in late adulthood (Study II); lower birth weight, placental size, and head circumference at 12 months predicted a more pronounced positive schitzotypal trait in women (Study III); and thinness and smaller head circumference at birth associated with symptoms of attention-deficit hyperactivity disorder (ADHD) in children who were born at term (Study IV). These associations occured across the whole variation in birth size and after adjusting for several confounders. With respect to growth after birth, individuals with high trait anxiety scores in late adulthood were lighter in weight and thinner in infancy, and gained weight more rapidly between 7 and 11 years of age, but weighed less and were shorter in late adulthood in relation to weight and height measured at 11 years of age (Study II). These results suggest that a suboptimal prenatal environment reflected in smaller birth size may affect a variety of psychological vulnerability factors for mental disorders, such as the temperamental trait of harm avoidance, trait anxiety, schizotypal traits, and symptoms of ADHD. The smaller the birth size across the whole range of variation, the more pronounced were these psychological vulnerability factors. Moreover, some of these outcomes, such as trait anxiety, were also predicted by patterns of growth after birth. The findings are concordant with the DOHaD model, and emphasise the importance of prenatal factors in the aetiology of not only mental disorders but also their psychological vulnerability factors.

Rice responses to soil management in a rice-based cropping system in the semi-arid tropics of southern Lombok, Eastern Indonesia

This paper is the first of a series that investigates whether new cropping systems with permanent raised beds (PRBs) or Flat land could be successfully used to increase farmers' incomes from rainfed crops in Lombok in Eastern Indonesia. This paper discusses the rice phase of the cropping system. Low grain yields of dry-seeded rice (Oryza sativa) grown on Flat land on Vertisols in the rainfed region of southern Lombok, Eastern Indonesia, are probably mainly due to (a) erratic rainfall (870-1220 mm/yr), with water often limiting at sensitive growth stages, (b) consistently high temperatures (average maximum - 31 C), and (c) low solar radiation. Farmers are therefore poor, and labour is hard and costly, as all operations are manual. Two replicated field experiments were run at Wakan (annual rainfall = 868 mm) and Kawo (1215 mm) for 3 years (2001/2002 to 2003/2004) on Vertisols in southern Lombok. Dry-seeded rice was grown in 4 treatments with or without manual tillage on (a) PRBs, 1.2 m wide, 200 mm high, separated by furrows 300 mm wide, 200 mill deep, with no rice sown in the well-graded furrows, and (b) well-graded Flat land. Excess surface water was harvested from each treatment and used for irrigation after the vegetative stage of the rice. All operations were manual. There were no differences between treatments in grain yield of rice (mean grain yield = 681 g/m(2)) which could be partly explained by total number of tillers/hill and mean panicle length, but not number of productive tillers/hill, plant height or weight of 1000 grains. When the data from both treatments on PRBs and from both treatments on Flat land, each year at each site were analysed, there were also no differences in grain yield of rice (g/m(2)). When rainfall in the wet season up to harvest was over 1000 mm (Year 2; Wakan, Kawo), or plants were water-stressed during crop establishment (Year 1; Wakan) or during grain-fill (Year 3: Kawo), there were significant differences in grain yield (g/1.5 m(2)) between treatments; generally the grain yield (g/1.5 m(2)) on PRBs with or without tillage was less than that on Flat land with or without tillage. However, when the data from both treatments on PRBs and from both treatments on Flat land, each year at each site, were analysed, the greater grain yield of dry-seeded rice on Flat land (mean yield 1 092 g/1.5 m(2)) than that on PRBs (mean 815 g/1.5 m(2)) was mainly because there were 25% more plants on Flat land. Overall when the data in the 2 outer rows and the 2 inner rows on PRBs were each combined, there was a higher number of productive tillers in the combined outer rows (mean 20.7 tillers/hill) compared with that in the combined inner rows on each PRB (mean 18.2 tillers/hill). However, there were no differences in grain yield between combined rows (mean 142 g/m row). Hence with a gap of 500 mm (the distance between the outer rows of plants on adjacent raised beds), plants did not compensate in grain yield for missing plants in furrows. This suggests that rice (a) also sown in furrows, or (b) sown in 7 rows with narrower row-spacing, or (c) sown in 6 rows with slightly wider row-spacing, and narrower gap between outer rows on adjacent beds, may further increase grain yield (g/1.5 m(2)) in this system of PRBs. The growth and the grain yield (y in g/m(2)) of rainfed rice (with rainfall on-site the only source of water for irrigation) depended mainly on the rainfall (x in mm) in the wet season up to harvest (due either to site or year) with y = 1. 1x -308; r(2) = 0.54; p < 0.005. However, 280 mm (i.e. 32%) of the rainfall was not directly used to produce grain (i.e. when y = 0 g/m(2)). Manual tillage did not affect growth and grain yield of rice (g/m(2); g/1.5 m(2)), either on PRB or on Flat land.

Biocontrol of Chromolaena odorata in Papua New Guinea

The status of biocontrol of Chromolaena odorata, a weed of significant agricultural importance in Papua New Guinea, is assessed. Chromolaena is confirmed present in 391 sites in 12 of the 20 provinces of PNG. A collaborative project on the biocontrol of chromolaena involving the PNG National Agricultural Research Institute and the Queensland Department of Primary Industries and Fisheries began in1998, with funding from ACIAR. Three agents, the moth Pareuchaetes pseudoinsulata, which has established only in Morobe Province, the stem-galling fly Cecidochares connexa, which has established in all 12 provinces and the leaf mining fly Calycomyza eupatorivora, which is currently being monitored for establishment, have been introduced. Cecidochares connexa has been the most effective of the agents so far and it has spread more than 100 km in five years from some release sites. Preliminary field data have shown that the numbers of galls per plant have increased, coupled with a decrease in plant height and percent plant cover. In parts of New Ireland and Sandaun provinces, C. connexa has controlled chromolaena, resulting in the regeneration of natural vegetation. In addition, some food gardens have been re-established where chromolaena had once taken over. Consequently, food production has increased and income generated from selling agricultural produce has increased two fold. There is also less time spent in clearing chromolaena from food gardens and plantations. The effectiveness of C. connexa has brought relief to many communities, which are helping in the distribution of the gall fly to other areas affected by chromolaena.

Genetics of heifer performance in 'wet' and 'dry' seasons and their relationships with steer performance in two tropical beef genotypes.

The genetics of heifer performance in tropical 'wet' and 'dry' seasons, and relationships with steer performance, were studied in Brahman (BRAH) and Tropical Composite (TCOMP) (50% Bos indicus, African Sanga or other tropically adapted Bos taurus; 50% non-tropically adapted Bos taurus) cattle of northern Australia. Data were from 2159 heifers (1027 BRAH, 1132 TCOMP), representing 54 BRAH and 51 TCOMP sires. Heifers were assessed after post-weaning 'wet' (ENDWET) and 'dry' (ENDDRY) seasons. Steers were assessed post-weaning, at feedlot entry, over a 70-day feed test, and after similar to 120-day finishing. Measures studied in both heifers and steers were liveweight (LWT), scanned rump fat, rib fat and M. longissimus area (SEMA), body condition score (CS), hip height (HH), serum insulin-like growth factor-I concentration (IGF-I), and average daily gains (ADG). Additional steer measures were scanned intra-muscular fat%, flight time, and daily (DFI) and residual feed intake (RFI). Uni- and bivariate analyses were conducted for combined genotypes and for individual genotypes. Genotype means were predicted for a subset of data involving 34 BRAH and 26 TCOMP sires. A meta-analysis of genetic correlation estimates examined how these were related to the difference between measurement environments for specific traits. There were genotype differences at the level of means, variances and genetic correlations. BRAH heifers were significantly (P < 0.05) faster-growing in the 'wet' season, slower-growing in the 'dry' season, lighter at ENDDRY, and taller and fatter with greater CS and IGF-I at both ENDWET and ENDDRY. Heritabilities were generally in the 20 to 60% range for both genotypes. Phenotypic and genetic variances, and genetic correlations, were commonly lower for BRAH. Differences were often explained by the long period of tropical adaptation of B. indicus. Genetic correlations were high between corresponding measures at ENDWET and ENDDRY, positive between fat and muscle measures in TCOMP but negative in BRAH (mean of 13 estimates 0.50 and -0.19, respectively), and approximately zero between steer feedlot ADG and heifer ADG in BRAH. Numerous genetic correlations between heifers and steers differed substantially from unity, especially in BRAH, suggesting there may be scope to select differently in the sexes where that would aid the differing roles of heifers and steers in production. Genetic correlations declined as measurement environments became more different, the rates of decline (environment sensitivity) sometimes differing with genotype. Similar measures (LWT, HH and ADG; IGF-I at ENDWET in TCOMP) were genetically correlated with steer DFI in heifers as in steers. Heifer SEMA was genetically correlated with steer feedlot RFI in BRAH (0.75 +/- 0.27 at ENDWET, 0.66 +/- 0.24 at ENDDRY). Selection to reduce steer RFI would reduce SEMA in BRAH heifers but otherwise have only small effects on heifers before their first joining.

Pre-release evaluation of the efficacy of the leaf-sucking bug Carvalhotingis visenda (Heteroptera: Tingidae) as a biological control agent for cat's claw creeper Macfadyena unguis-cati (Bignoniaceae)

In classical weed biological control, assessing weed response to simulated herbivory is one option to assist in the prioritization of available agents and prediction of their potential efficacy. Previously reported simulated herbivory studies suggested that a specialist herbivore in the leaf-feeding guild is desirable as an effective biological control agent for cat's claw creeper Macfadyena unguis-cati (Bignoniaceae), an environmental weed that is currently a target for biological control. In this study, we tested (i) whether the results from glasshouse-based simulated herbivory can be used to prioritise potential biological control agents by evaluating the impact of a leaf-sucking tingid bug Carvalhotingis visenda (Drake & Hambleton) (Hemiptera: Tingidae) in quarantine; and (ii) the likely effectiveness of low- and high-densities of the leaf-sucking tingid after its release in the field. The results suggest that a single generation of C. visenda has the potential to reduce leaf chlorophyll content significantly, resulting in reduced plant height and leaf biomass. However, the impact of one generation of tingid herbivory on below-ground plant components, including the roots and tuber size and biomass, were not significant. These findings are consistent with results obtained from a simulated herbivory trial, highlighting the potential role of simulated herbivory studies in agent prioritisation.

Functional dynamics of the nitrogen balance of sorghum. II. Grain filling period.

Maintenance of green leaf area during grain filling can increase grain yield of sorghum grown under terminal water limitation. This 'stay-green' trait has been related to the nitrogen (N) supply-demand balance during grain filling. This study quantifies the N demand of grain and N translocation rates from leaves and stem and explores effects of genotype and N stress on onset and rate of leaf senescence during the grain filling period. Three hybrids differing in potential height were grown at three levels of N supply under well-watered conditions. Vertical profiles of biomass, leaf area, and N% of leaves, stem and grain were measured at regular intervals. Weekly SPAD chlorophyll readings on main shoot leaves were correlated with observed specific leaf nitrogen (SLN) to derive seasonal patterns of leaf N content. For all hybrids, individual grain N demand was sink determined and was initially met through N translocation from the stem and rachis. Only if this was insufficient did leaf N translocation occur. Maximum N translocation rates from leaves and stem were dependent on their N status. However, the supply of N at canopy scale was also related to the amount of leaf area senescing at any one time. This supply-demand framework for N dynamics explained effects of N stress and genotype on the onset and rate of leaf senescence.

Functional dynamics of the nitrogen balance of sorghum: I. N demand of vegetative plant parts.

Stay-green, an important trait for grain yield of sorghum grown under water limitation, has been associated with a high leaf nitrogen content at the start of grain filling. This study quantifies the N demand of leaves and stems and explores effects of N stress on the N balance of vegetative plant parts of three sorghum hybrids differing in potential crop height. The hybrids were grown under well-watered conditions at three levels of N supply. Vertical profiles of biomass and N% of leaves and stems, together with leaf size and number, and specific leaf nitrogen (SLN), were measured at regular intervals. The hybrids had similar minimum but different critical and maximum SLN, associated with differences in leaf size and N partitioning, the latter associated with differences in plant height. N demand of expanding new leaves was represented by critical SLN, and structural stem N demand by minimum stem N%. The fraction of N partitioned to leaf blades increased under N stress. A framework for N dynamics of leaves and stems is developed that captures effects of N stress and genotype on N partitioning and on critical and maximum SLN.

Pest-damage relationships for Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on vegetative soybean.

The response of vegetative soybean (Glycine max) to Helicoverpa armigera feeding was studied in irrigated field cages over three years in eastern Australia to determine the relationship between larval density and yield loss, and to develop economic injury levels. Rather than using artificial defoliation techniques, plants were infested with either eggs or larvae of H. armigera, and larvae allowed to feed until death or pupation. Larvae were counted and sized regularly and infestation intensity was calculated in Helicoverpa injury equivalent (HIE) units, where 1 HIE was the consumption of one larva from the start of the infestation period to pupation. In the two experiments where yield loss occurred, the upper threshold for zero yield loss was 7.51 ± 0.21 HIEs and 6.43 ± 1.08 HIEs respectively. In the third experiment, infestation intensity was lower and no loss of seed yield was detected up to 7.0 HIEs. The rate of yield loss/HIE beyond the zero yield loss threshold varied between Experiments 1 and 2 (-9.44 ± 0.80 g and -23.17 ± 3.18 g, respectively). H. armigera infestation also affected plant height and various yield components (including pod and seed numbers and seeds/pod) but did not affect seed size in any experiment. Leaf area loss of plants averaged 841 and 1025 cm2/larva in the two experiments compared to 214 and 302 cm2/larva for cohort larvae feeding on detached leaves at the same time, making clear that artificial defoliation techniques are unsuitable for determining H. armigera economic injury levels on vegetative soybean. Analysis of canopy leaf area and pod profiles indicated that leaf and pod loss occurred from the top of the plant downwards. However, there was an increase in pod numbers closer to the ground at higher pest densities as the plant attempted to compensate for damage. Defoliation at the damage threshold was 18.6 and 28.0% in Experiments 1 and 2, indicating that yield loss from H. armigera feeding occurred at much lower levels of defoliation than previously indicated by artificial defoliation studies. Based on these results, the economic injury level for H. armigera on vegetative soybean is approximately 7.3 HIEs/row-metre in 91 cm rows or 8.0 HIEs/m2.

A new semi-dwarfing gene identified by molecular mapping of quantitative trait loci in barley.

Semi-dwarfing genes have been widely used in spring barley (Hordeum vulgare L.) breeding programs in many parts of the world, but the success in developing barley cultivars with semi-dwarfing genes has been limited in North America. Exploiting new semi-dwarfing genes may help in solving this dilemma. A recombinant inbred line population was developed by crossing ZAU 7, a semi-dwarf cultivar from China, to ND16092, a tall breeding line from North Dakota. To identify quantitative trait loci (QTL) controlling plant height, a linkage map comprised of 111 molecular markers was constructed. Simple interval mapping was performed for each of the eight environments. A consistent QTL for plant height was found on chromosome 7HL. This QTL is not associated with maturity and rachis internode length. We suggest the provisional name Qph-7H for this QTL. Qph-7H from ZAU 7 reduced plant height to about 3/4 of normal; thus, Qph-7H is considered a semi-dwarfing gene. Other QTLs for plant height were found, but their expression was variable across the eight environments tested.

The performance of irrigated mixtures of tall fescue, ryegrass and white clover in subtropical Australia. 1. The effects of sowing mixture combinations, nitrogen and oversowing on establishment, productivity, botanical composition and persistence.

In the subtropics of Australia, the ryegrass component of irrigated perennial ryegrass (Lolium perenne) - white clover (Trifolium repens) pastures declines by approximately 40% in the summer following establishment, being replaced by summer-active C4 grasses. Tall fescue (Festuca arundinacea) is more persistent than perennial ryegrass and might resist this invasion, although tall fescue does not compete vigorously as a seedling. This series of experiments investigated the influence of ryegrass and tall fescue genotype, sowing time and sowing mixture as a means of improving tall fescue establishment and the productivity and persistence of tall fescue, ryegrass and white clover-based mixtures in a subtropical environment. Tall fescue frequency at the end of the establishment year decreased as the number of companion species sown in the mixture increased. Neither sowing mixture combinations nor sowing rates influenced overall pasture yield (of around 14 t/ha) in the establishment year but had a significant effect on botanical composition and component yields. Perennial ryegrass was less competitive than short-rotation ryegrass, increasing first-year yields of tall fescue by 40% in one experiment and by 10% in another but total yield was unaffected. The higher establishment-year yield (3.5 t/ha) allowed Dovey tall fescue to compete more successfully with the remaining pasture components than Vulcan (1.4 t/ha). Sowing 2 ryegrass cultivars in the mixture reduced tall fescue yields by 30% compared with a single ryegrass (1.6 t/ha), although tall fescue alone achieved higher yields (7.1 t/ha). Component sowing rate had little influence on composition or yield. Oversowing the ryegrass component into a 6-week-old sward of tall fescue and white clover improved tall fescue, white clover and overall yields in the establishment year by 83, 17 and 11%, respectively, but reduced ryegrass yields by 40%. The inclusion of red (T. pratense) and Persian (T. resupinatum) clovers and chicory (Cichorium intybus) increased first-year yields by 25% but suppressed perennial grass and clover components. Yields were generally maintained at around 12 t/ha/yr in the second and third years, with tall fescue becoming dominant in all 3 experiments. The lower tall fescue seeding rate used in the first experiment resulted in tall fescue dominance in the second year following establishment, whereas in Experiments 2 and 3 dominance occurred by the end of the first year. Invasion by the C4 grasses was relatively minor (<10%) even in the third year. As ryegrass plants died, tall fescue and, to a lesser extent, white clover increased as a proportion of the total sward. Treatment effects continued into the second, but rarely the third, year and mostly affected the yield of one of the components rather than total cumulative yield. Once tall fescue became dominant, it was difficult to re-introduce other pasture components, even following removal of foliage and moderate renovation. Severe renovation (reducing the tall fescue population by at least 30%) seems a possible option for redressing this situation.

Effect of position on precision within the recording field of a markerless motion capture system

Introduction Markerless motion capture systems are relatively new devices that can significantly speed up capturing full body motion. A precision of the assessment of the finger’s position with this type of equipment was evaluated at 17.30 ± 9.56 mm when compare to an active marker system [1]. The Microsoft Kinect was proposed to standardized and enhanced clinical evaluation of patients with hemiplegic cerebral palsy [2]. Markerless motion capture systems have the potential to be used in a clinical setting for movement analysis, as well as for large cohort research. However, the precision of such system needs to be characterized. Global objectives • To assess the precision within the recording field of the markerless motion capture system Openstage 2 (Organic Motion, NY). • To compare the markerless motion capture system with an optoelectric motion capture system with active markers. Specific objectives • To assess the noise of a static body at 13 different location within the recording field of the markerless motion capture system. • To assess the smallest oscillation detected by the markerless motion capture system. • To assess the difference between both systems regarding the body joint angle measurement. Methods Equipment • OpenStage® 2 (Organic Motion, NY) o Markerless motion capture system o 16 video cameras (acquisition rate : 60Hz) o Recording zone : 4m * 5m * 2.4m (depth * width * height) o Provide position and angle of 23 different body segments • VisualeyezTM VZ4000 (PhoeniX Technologies Incorporated, BC) o Optoelectric motion capture system with active markers o 4 trackers system (total of 12 cameras) o Accuracy : 0.5~0.7mm Protocol & Analysis • Static noise: o Motion recording of an humanoid mannequin was done in 13 different locations o RMSE was calculated for each segment in each location • Smallest oscillation detected: o Small oscillations were induced to the humanoid mannequin and motion was recorded until it stopped. o Correlation between the displacement of the head recorded by both systems was measured. A corresponding magnitude was also measured. • Body joints angle: o Body motion was recorded simultaneously with both systems (left side only). o 6 participants (3 females; 32.7 ± 9.4 years old) • Tasks: Walk, Squat, Shoulder flexion & abduction, Elbow flexion, Wrist extension, Pronation / supination (not in results), Head flexion & rotation (not in results), Leg rotation (not in results), Trunk rotation (not in results) o Several body joint angles were measured with both systems. o RMSE was calculated between signals of both systems. Results Conclusion Results show that the Organic Motion markerless system has the potential to be used for assessment of clinical motor symptoms or motor performances However, the following points should be considered: • Precision of the Openstage system varied within the recording field. • Precision is not constant between limb segments. • The error seems to be higher close to the range of motion extremities.