A question which has arisen clinically is the inability to generate adequate vertical force during the second half of the stance phase in cerebral palsy gait. Neither the mechanism nor the consequences of this inability are understood. It implies that the centre of mass (CoM) is inadequately supported with the potential for collapse of the limb in single support. Normal walking is achieved by the sophisticated control of the neuromuscular and skeletal systems with the purpose of advancing the body with minimum energy expenditure. These control systems are affected by damage to the brain in children with cerebral palsy and result in a multitude of problems which affect their gait making it difficult to determine cause and effect. This study aimed to improve the understanding of the ground reaction forces and motion of the CoM. Objectives The principle objectives were to analyse the supporting forces of the CoM during gait in normal adults, children, and children with diplegic cerebral palsy, by examining the inter-relationships of the vertical and horizontal components of the ground reaction force with the vertical component of motion and temporal parameters of the CoM. Design The study of adults and children’s data was both prospective and retrospective. The study of cerebral palsy data was retrospective. A new software programme was developed to extract specific gait parameters from both normal and cerebral palsy gait patterns. A novel approach to analyse the interaction of motion and force data in normal walking was subsequently developed. Background In normal gait, the vertical component of the ground reaction force forms a double hump where both humps are equal in magnitude and greater than body weight. It is widely accepted that the first hump (FZ1) is associated with deceleration of the downward motion of the CoM as the foot “impacts” the ground and the second hump (FZ2) is the action of “push off” as the body is propelled upwards and forwards. Walking requires force contributions from both legs but traditionally computed three-dimensional (3D) gait analysis packages presents the force data with both legs superimposed, rather than sequentially in time. This gives the impression that there is no period of overlap of the forces and thus ignores the critically important period where the CoM is transferred from one leg to the other during double support. By changing the presentation to view it sequentially in time, plus superimposing the CoM kinematics onto the same scale allowed their interactions to be observed and objectively measured. Methods The kinematic and kinetic data of 53 normal adults, 33 normal children, and 57 diplegic cerebral palsy children were acquired for the study. A new gait cycle, based on CoM motion, was defined to allow analysis of the forces in relation to CoM motion. Software was developed to extract specified parameters from the gait data. Impulse calculations over specific periods (based on the vertical motion of the CoM) allowed analysis of the vertical force contribution of each leg to the vertical support of the CoM. Results The results showed that inadequate generation of vertical force in children with diplegic cerebral palsy was widespread. In approximately 40% of such children there was a reduced ability to generate an adequate FZ2, which resulted in a reduced ability to control of the descent velocity of the CoM. The mean reduction in descent velocity in cerebral palsy was only 54% compared to 86% in adults. Integration of the vertical force and motion of the CoM showed that FZ2 was associated with controlling the descent velocity of the CoM. This reverses the traditionally accepted concept of “impact” and is contrary to the belief that FZ2 is associated with ‘push off’. Conclusions and Relevance This study emphasises the importance of the role of the supporting leg in the second half of stance. Failure to generate an adequate FZ2, which is currently ignored in clinical practice, should be given priority in patient management. This new knowledge has significant implications from a clinical perspective, not only in diplegic cerebral palsy, but in pathologies such as amputees, spina-bifida, and other neuro-muscular conditions.

Aim: The aim of this study was to investigate the differences between older and younger adults in the attenuation of impact during descent from a step. Strategies that have been implicated in reducing either the magnitude of vertical ground reaction force (vertical GRF) or the time taken to reach the maximum vertical GRF in the stepping leg were explored. Study Design: The study was an experimental, laboratory based, repeated measures design. Participants: Twenty participants took part in this exploratory study. Ten in the older group of 60-80 years, mean 65.3 (SD 5) years and ten in the younger age group of 20-30 years, mean 22.8 (SD 2.5) years. Main Measures: The vertical GRF and the time taken to reach maximum vertical GRF were measured to ascertain impact during step descent. Electromyography and kinematic variables were measured to determine the effect they may have on the impact. The variables measured were the maximum joint range of motion of the hip and knee during early stance in step descent. Surface electromyography from four lower limb muscles was recorded to ascertain the magnitude of muscle activity at impact. The relationship in an antero-posterior direction of the upper body and stepping leg at initial contact (IC) was also investigated. Results: There was a significant difference in both the amount of knee flexion and the amount of activity of the vastus lateralis muscle during impact between older and younger adults. Older adults had significantly less knee flexion during a step descent activity than younger adults (F(1,18)=5.48; p=.031).Older adults had significantly more vastus lateralis activity during a step descent activity than younger adults (F(1,18)=5.21; p=.035). Conclusions: Older and younger adults use different strategies in both muscle activation and joint range of motion around the knee of the leading leg during the step descent. Older adults used more vastus lateralis activity perhaps to increase stiffness in the knee, leading to a reduction in range of motion at impact. Although no change in vertical GRF was detected in this study, both of these strategies have the potential to increase the impact of a step and therefore cause jarring and possible damage. This study recruited healthy active older adults and differences in impact may be observed in an older or less active population, or in those with joint pathology such as osteoarthritis.

Aim: The aim of this study was to investigate the differences between older and younger adults in the attenuation of impact during descent from a step. Strategies that have been implicated in reducing either the magnitude of vertical ground reaction force (vertical GRF) or the time taken to reach the maximum vertical GRF in the stepping leg were explored. Study Design: The study was an experimental, laboratory based, repeated measures design. Participants: Twenty participants took part in this exploratory study. Ten in the older group of 60-80 years, mean 65.3 (SD 5) years and ten in the younger age group of 20-30 years, mean 22.8 (SD 2.5) years. Main Measures: The vertical GRF and the time taken to reach maximum vertical GRF were measured to ascertain impact during step descent. Electromyography and kinematic variables were measured to determine the effect they may have on the impact. The variables measured were the maximum joint range of motion of the hip and knee during early stance in step descent. Surface electromyography from four lower limb muscles was recorded to ascertain the magnitude of muscle activity at impact. The relationship in an antero-posterior direction of the upper body and stepping leg at initial contact (IC) was also investigated. Results: There was a significant difference in both the amount of knee flexion and the amount of activity of the vastus lateralis muscle during impact between older and younger adults. Older adults had significantly less knee flexion during a step descent activity than younger adults (F(1,18)=5.48; p=.031).Older adults had significantly more vastus lateralis activity during a step descent activity than younger adults (F(1,18)=5.21; p=.035). Conclusions: Older and younger adults use different strategies in both muscle activation and joint range of motion around the knee of the leading leg during the step descent. Older adults used more vastus lateralis activity perhaps to increase stiffness in the knee, leading to a reduction in range of motion at impact. Although no change in vertical GRF was detected in this study, both of these strategies have the potential to increase the impact of a step and therefore cause jarring and possible damage. This study recruited healthy active older adults and differences in impact may be observed in an older or less active population, or in those with joint pathology such as osteoarthritis.

Thesis (PhD) - Swinburne University of Technology, Faculty of Engineering and Industrial Sciences, 2006. / A thesis submitted for the degree of Doctor of Philosophy, [Faculty of Engineering and Industrial Sciences], Swinburne University of Technology, 2006. Typescript. Includes bibliographical references (p. 251-256)

Thesis (M.S.)--Brigham Young University. Dept. of Exercise Sciences, 2007. / Includes bibliographical references.

Thesis (M.S.)--Michigan State University, 2006. / Includes bibliographical references (leaves 91-100). Also available online (PDF file) by a subscription to the set or by purchasing the individual file.

Thesis (M.S.)--Michigan State University, 2006. / Includes bibliographical references (leaves 91-100).

Morton’s syndrome is a foot condition where the 1st metatarsal does not protrude as far distally as the 2nd metatarsal. Clinicians believe that short 1st metatarsal protrusion affects foot mechanics and leads to painful conditions of the foot. Normal protrusion ratio of the 1st and 2nd metatarsal has not been delineated in scientific literature, and little is known about the mechanics of feet with short 1st metatarsal protrusion beyond anecdotal clinical evidence. In the first part of this two-part study, a novel tool was developed to guide metatarsal measurement and reduce measurement error so values for normal metatarsal protrusion ratios could be established. In the second part, subjects were divided into those with shorter and longer than average 1st metatarsal protrusion ratio and we measured if there were any differences in the foot-floor forces between the two groups. In Part 1, the feet of 65 healthy subjects were measured with a novel measurement tool and it was determined that the average ratio (1st metatarsal/2nd metatarsal) was 0.902, suggesting a 1st metatarsal that does not protrude as far distally as the 2nd metatarsal. For Part 2, participants were divided into two groups: the short 1st metatarsal group had a ratio of more than one standard deviation below the mean (0.866 or lower) while the control group had a metatarsal ratio of more than one standard deviation above the mean (0.938 or higher). We hypothesized that short 1st metatarsal protrusion would cause an imbalance across the forefoot because the 1st metatarsal would not be able to carry the required load on the medial side of the foot; however, the results of the gait study did not show this as only forces in the walking direction near toe-off correlated with metatarsal protrusion ratio. We can only speculate as to the relationship between the metatarsal protrusion ratio and increased shear force in the walking direction, but it is possible that to compensate for the diminished stabilizing capacity of the shorter 1st metatarsal, the foot must push off with more force to propel the body forward. / Thesis (Master, Rehabilitation Science) -- Queen's University, 2013-01-14 14:38:55.255

O objetivo do presente estudo foi de analisar as respostas de ativação muscular e força de reação do solo de um exercício de hidroginástica com diferentes equipamentos, executado por mulheres jovens. Sendo assim, foram realizados três testes progressivos máximos em ambiente aquático, com no mínimo 48 horas de intervalo, com o exercício de chute, sem equipamento (SE), com equipamento resistivo (RE) e flutuante (FL), a fim de determinar a cadência correspondente ao segundo limiar ventilatório (LV2). O terceiro e último dia de testes consistiu primeiramente na contração voluntária isométrica máxima (CVM) em ambiente terrestre, dos músculos a serem avaliados: reto femoral (RF), bíceps femoral (BF), tibial anterior (TA) e gastrocnêmio lateral (GA). Após finalizada a CVM de cada músculo, foi feito um isolamento dos eletrodos, e então o sujeito entrou na piscina para realizar os testes de eletromiografia (EMG) e força de reação do solo (FRS) nas intensidades do LV2 e máximo esforço (MAX). Dentro da piscina, o sujeito foi posicionado na profundidade do processo xifóide e então, executou as três situações do exercício de chute (SE, RE e FL), de forma randomizada, nas intensidades LV2 e máximo esforço (MAX). Foi utilizada o teste estatístico de Equações estimativas generalizadas e o teste post-hoc de Bonferroni. Após o tratamento dos dados e análise estatística, foram encontrados maiores valores de ativação muscular da intensidade LV2 para MAX, para todas as situações nos músculos RF, BF e TA, exceto para GL que não obteve diferenças entre intensidades para a situação RE. Comparando as situações, não houve diferenças significativas entre as mesmas para RF, BF e TA, exceto para o músculo GLque obteve menores valores de ativação para a situação RE comparada à SE. Para os resultados de FRS, foram encontrados maiores valores para a intensidade MAX para as situações SE e RE, enquanto para FL, não foram encontradas diferenças de FRS entre as intensidades. Comparando as situações, FL obteve menores valores comparado à SE e RE, nas duas intensidades. Para os resultados de impulso (IMP), foram encontradas diferenças significavamente menores para a intensidade MAX para todas as situações, com menores valores de IMP na situação FL. A partir dos resultados encontrados no 6 presente estudo, de uma maneira geral, a utilização de equipamentos tanto RE quanto FL, parece não influenciar a ativação muscular durante a execução do exercício CH, além disso, a intensidade MAX elicita maiores valores de ativação. Além disso, apesar de terem sido encontradas diferenças de FRS e IMP entre as intensidades, o equipamento FL obteve menores valores de FRS e IMP, sem diferenças entre LV2 e MAX na FRS, demonstrando que apesar de obter uma maior ativação muscular em MAX, não houve um aumento significativo de FRS nesta intensidade. Sendo assim, a utilização de equipamentos parece influenciar principalmente a variável de FRS, reduzindo estes valores e tornando o exercício de CH mais seguro quando é necessária uma menor sobrecarga articular, enquanto a ativação muscular não se difere das outras situações. / The aim of the presente study was to analyze the muscle activation and ground reaction forces responses of one hydrogymnastic exercise performed by women with different devices. Three sessions of water progressive testes were conducted with 48 hours of interval with the frontal kick exercise (FK) without devices (WD), with resistance devices (RD) and floating devices (FD), to determine the cadence corresponding to the second ventilatory threshold (VT2).The third and last day of tests consisted iniciated with the maximum voluntary contraction (MVC) of the muscles to be analyzed: rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA) and gastrocnemius lateralis (GL). After that, the electrodes were isolated and than the subject entered the pool (immersion on the xifoide process) to perform the electromiography (EMG) and ground reaction forces (GRF) tests in VT2 and maximum (MAX) intensity. Generalized estimating equation and Bonferroni’s test were used for the statistical analyses. The results showed higher muscle activity for the MAX comparing to VT2 for RF, BF and TA, except for GL muscle, which didn’t achieve difference between the intensities for RD. Comparing the three situations, there was no significant difference between. In VT2 and MAX there was no difference between all situations, except for GL in MAX, which obtained lower values for RD compared with FD. The ground reaction forces results showed higher values for the MAX intensity for the WD and RD situations, while for FD there was no difference between VT2 and MAX. Comparing the situations, FD obtained lower values compared with WD and RD in both intensities. For impulse (IMP), significant lower values were founde for the MAX intensity for all situations, with lower values for FD. According to the results, it might be concluded that the use of devices seems to not influence the muscle activity during the FK exercise, besides that, the MAX intensity elicits higher results. Despite the differences for GRF and IMP, the FL situation leads to a higher muscle activation in MAX while there is no GRF increase from VT2. Therefore, the use of devices appears to influence mostly the GRF variable, showing lowest values for this situation comparing to WD and RD making FK safer when a lower joint overload is needed, while the muscle activation didn’t differ from WD and RD.

The purpose of this study was to examine the independent effects of anterior knee pain (AKP) on bilateral ground reaction force (GRF) during running, with a focus on GRF applied to the uninvolved leg, which, prior to this study, had never been evaluated. Twelve volunteers completed three data collection sessions, that corresponded to one of three conditions (control, sham, and pain), in a counterbalanced order. For each session, subjects ran for five minutes. For the pain and sham sessions, respectively, hypertonic and isotonic saline were infused into the infrapatellar fat pad of the right leg during the running, while no infusion was involved in the control session. GRF data were collected during the final 30 seconds of running. Functional statistics were used to determine the effects of session and leg (right and left) on vertical and anterior-posterior GRF throughout the stance phase of running. A mixed model ANOVA was used to determine the effect of session and leg on vertical GRF load rate, impulse due to vertical, propulsive, and braking GRFs. A repeated measures ANOVA was used to determine the effect of session and time on subject-perceived pain. Alpha was set to 0.05 for all statistical comparisons. Unexpectedly, no significant session × leg interaction existed for vertical GRF at any time point during stance phase of running. Similarly, the experimental AKP did not affect impulse due to vertical GRF or load rate for the vertical GRF. There was, however, a significant session × leg interaction for anterior-posterior GRF. For the pain session, involved-leg braking GRF was 11% greater than uninvolved-leg braking GRF, during the first 9% of stance phase. There was also a significant between-session difference for involved-leg braking impulse (p = 0.023) and uninvolved-leg propulsive impulse (p = 0.027). The mean involved-leg braking impulses were 11.3 Ns (± 0.6), 13.2 Ns (± 0.6) and 13.2 Ns (± 0.6) for the pain, control, and sham sessions, respectively. Mean uninvolved-leg propulsive impulses were 14.8 Ns (± 1.3), 13.6 Ns (± 1.3), and 13.5 Ns (± 1.3) for the pain, control, and sham sessions, respectively. These differences in anterior-posterior GRF might reflect a compensatory unloading of the involved leg due to AKP.