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.

The purpose of this study was to compare joint moments during the active peak vertical ground reaction force (PVGRF) when running in three conditions. Twenty-five subjects, sixteen male and nine female, were measured using 3-dimensional motion analysis while running barefoot, in Vibram FiveFingers® (VF®) minimalist running shoes and in traditional running shoes at a 7-minute-mile pace (3.84 m/s). Joint moment differences were calculated and compared using a mixed model analysis of variance. Results showed the VF® was effective at mimicking both the kinetic and kinematic attributes of barefoot running. The only significant difference found when comparing barefoot and VF® running was in the ankle angle (p < .005). All other variables in the lower extremity were the same for the two conditions. Though the subjects in our study had no previous experience with VF® (or barefoot) running they were able to closely mimic barefoot running upon initial running trials. Joint moments at the ankle were higher for barefoot and VF® running (p < .001) when compared with shod running. This may potentially lead to a greater risk of injury at the ankle joint when running barefoot or in VF®. The hip joint moments were only different when comparing the barefoot condition to the shod condition (p=.002), with the barefoot condition higher than shod running. The knee joint moment was smaller during the VF® and barefoot conditions when compared with shod running (p < .001) and may lead to a decrease in injury rates at the knee. Though a reduction in moments of the lower extremity may lead to a decrease of injury at the corresponding joint, it is important to consider the adaptations that take place as a result of varying stresses. According to Wolff's law, bone and surrounding tissue will adapt to the loads it is placed under. Taking this into consideration, it is important to remember that lower moments may lead to weaker bones and surrounding tissues and without compensation for these reduced loads, injury rates may remain the same over time.

No description available.

Context: Abdominal training may decrease the risk of lower extremity injuries through improved balance and postural control. Objective: To determine the effect of an eight-week abdominal-training program on center of pressure, lower extremity joint angles, and abdominal muscle activation during a single-leg drop landing. The effects of abdominal training on abdominal muscle thickness was assessed. Design: A cohort research design. Setting: Research laboratory. Other Participants: Sixty healthy physically active college-aged students participated. They were divided into three groups: Control, Chronic ankle instability (CAI), and Healthy. Nineteen Control (age = 22.0 ± 2.72 yrs, mass = 74.1 ± 13.8 kg, height = 172.6 ± 11.3 cm, BMI = 24.8 ± 3.1 %), 21 CAI (age = 22.1 ± 2.3 yrs, mass = 77.6 ± 14.0 kg, height = 175.4 ± 12.3 cm, BMI = 25.1 ± 2.6 %), and 20 healthy (age = 22.9 ± 3.4 yrs, mass = 70.9 ± 15.6 kg, height = 172.2 ± 8.9 cm, BMI = 23.7 ± 3.3 %). Subjects in the CAI group had a history of CAI and functional ankle instability (FAI). The Ankle Instability Index and the Functional Ankle Ability Measure were used to self-report CAI and FAI respectively. Interventions: The CAI and Healthy groups participated in an eight-week abdominal-training program while the Control group maintained their normal activities of daily living and level of physical activity. Main Outcome Measures: Abdominal muscle thickness was measured biweekly throughout the study. Center of pressure excursion, muscle activation, vertical ground reaction force, and lower extremity joint angles were measured during a single-leg drop landing, pre- and postabdominal training. Results: Muscle thickness at rest increased in the rectus abdominis and external oblique muscles follow training. Eight weeks of abdominal training decreased vertical ground reaction forces and muscle activation down the lower kinetic chain. Center of pressure excursion and velocity were increased following training. Conclusions: Eight-weeks of abdominal training increased abdominal muscle thickness. Training improved neuromuscular efficiency throughout the kinetic chain and may have improved dynamic postural control. Our data also suggest CAI subjects may utilize both feedforward and feedback mechanisms to maintain postural control.

Context: Knee pain is a common symptom in knee pathology and is associated with alterations in quadriceps activation and movement patterns. Reducing pain through intervention may help reestablish neuromuscular function. The independent effects of knee pain are difficult to examine and unclear. Objective: To investigate the effects of transcutaneous electrical nerve stimulation (TENS) on quadriceps activation and vertical ground reaction force (VGRF) during walking. Design: Crossover. Setting: Laboratory. Subjects: 15 in the TENS group (10M and 5F, 23.5 ± 2.8 yrs, 70.5 ± 12.5 kg, 178.1 ± 7.4 cm), and 15 in the sham group (10M and 5F, 22.5 ± 2.0 yrs, 72.1 ± 13.7 kg, 177.5 ± 9.3 cm). Interventions: Subjects underwent three experimental conditions (pain, sham, and control). Measurements were recorded across four time points (preinfusion, infusion, treatment, and posttreatment). Hypertonic or isotonic saline, respectively, was infused into the infrapatellar fat pad for 48 minutes (total 7.7 mL). The TENS group received a 20-minute treatment. A sham treatment was administered to the sham group. Main Outcome Measures: Perceived knee pain on a 10-cm visual analog scale, knee extension maximum voluntary isometric contraction (MVIC) normalized to body mass, knee extension central activation ratio (CAR), and VGRF. Results: Knee pain peaked at 4 cm during infusion and remained consistent across time in the sham group (F2,28 = 49.90, P < 0.0001), while knee pain gradually decreased to 1.5 cm following TENS treatment (F2,28 = 23.11, P < 0.0001). A group x condition x time interaction was detected for both the MVIC (F6,168 = 2.92, P < 0.01) and CAR (F6,168 = 3.03, P < 0.008) measurements. Post hoc analysis revealed that the infusion of hypertonic saline reduced knee extension MVIC by 29% in the TENS group, and by 26% in the sham group (P < 0.05). However, while the MVIC remained depressed by 26% following sham treatment, the MVIC was found to improve by 12% following TENS treatment (P < 0.05). Similarly, a 10% decrease in CAR was detected in both sham and TENS groups prior to treatment. This 10% deficit held, with a 9% deficit following sham treatment, while the deficit of CAR was improved by 4% following TENS treatment (P < 0.05). For the TENS group, infusion of hypertonic saline changed VGRF at initial loading, midstance, and push-off phase. VGRF was only different at initial loading and push-off phase following TENS treatment. For the sham group however, sham treatment did not restore VGRF, showing alterations in initial loading, midstance, and push-off phase (α = 0.05). Conclusions: Infusion of hypertonic saline increased perceived knee pain, reduced knee extension MVIC, reduced CAR, and altered VGRF over some of stance phase. TENS lessened the deficits in MVIC, CAR, and VGRF, suggesting decreased muscle inhibition and improved movement function.

No description available.

La marche est définie par des séquences de gestes cycliques et répétées. Il a été déjà montré que la vitesse et la variabilité de ces séquences peuvent révéler des aptitudes ou des défaillances motrices. L’originalité de ce travail est alors d’analyser et de caractériser les foulées de sujets âgés à partir des signaux de pression issus de semelles instrumentées lors de la marche, au moyen d’outils de traitement du signal. Une étude préliminaire, sur les signaux de pression générés lors de la marche, nous a permis de mettre en évidence le caractère cyclo-stationnaire de ces signaux. Ces paramètres sont testées sur une population de 47 sujets. Tout d'abord, nous avons commencé par un prétraitement des signaux et nous avons montré dans la première de cette thèse que le filtrage peut éliminer une partie vitale du signal. C’est pourquoi un filtre adaptatif basé sur la décomposition en mode empirique a été conçu. Les points de retournement ont été filtrés ensuite en utilisant une technique temps-fréquence appelée «synochronosqueezing». Nous avons également montré que le contenu des signaux de force de marche est fortement affecté par des paramètres inquantifiables tels que les tâches cognitives qui les rendent difficiles à normaliser. C’est pourquoi les paramètres extraits de nos signaux sont tous dérivées par une comparaison inter-sujet. Par exemple, nous avons assimilé la différence dans la répartition de poids entre les pieds. Il est également recommandé dans ce travail de choisir le centre des capteurs plutôt que de compter sur la somme des forces issues du réseau de capteurs pour la classification. Ensuite, on a montré que l’hypothèse de la marche équilibrée et déséquilibrée peut améliorer les résultats de la classification. Le potentiel de cette hypothèse est montré à l'aide de la répartition du poids ainsi que le produit de l'âge × vitesse dans le premier classificateur et la corrélation dans le second classificateur. Une simulation de la série temporelle de VGRF basé sur une version modifiée du modèle de Markov non stationnaire, du premier ordre est ensuite dérivée. Ce modèle prédit les allures chez les sujets normaux et suffisamment pour les allures des sujets de Parkinson. On a trouvé que les trois modes: temps, fréquence et espace sont très utiles pour l’analyse des signaux de force, c’est pourquoi l’analyse de facteurs parallèles est introduite comme étant une méthode de tenseur qui peut être utilisée dans le futur / Walking is defined as sequences of repetitive cyclic gestures. It was already shown that the speed and the variability of these sequences can reveal abilities or motorskill failures. The originality of this work is to analyze and characterize the steps of elderly persons by using pressure signals. In a preliminary study, we showed that pressure signals are characterized by cyclostationarity. In this study, we intend to exploit the nonstationarity of the signals in a search for new indicators that can help in gait signal classification between normal and Parkinson subjects in the elderly population. These parameters are tested on a population of 47 subjects. First, we started with preprocessing the vertical ground reaction force (VGRF) signals and showed in this first part of the thesis that filtering can remove a vital part of the signal. That is why an adaptive filter based on empirical mode decomposition (EMD) was built. Turning points are filtered using synochronosqueezing of time-frequency representations of the signal. We also showed that the content of gait force signals is highly affected by unquantifiable parameter such as cognitive tasks which make them hard to be normalized. That is why features being extracted are derived from inter-subject comparison. For example we equated the difference in the load distribution between feet. It is also recommended in this work to choose the mid-sensor rather than relying on summation of forces from array of sensors for classification purposes. A hypothesis of balanced and unbalanced gait is verified to be potential in improving the classification accuracy. The power of this hypothesis is shown by using the load distribution and Age×Speed in the first classifier and the correlation in the second classifier. A time series simulation of VGRF based on a modified version of nonstationary- Markov model of first order is derived. This model successfully predict gaits in normal subjects and fairly did in Parkinson’s gait. We found out that the three modes: time, frequency and space are helpful in analyzing force signals that is why parallel factor analysis is introduced as a tensor method to be used in a future work