ENERGETICS OF THE LOWER EXTREMITY JOINTS DURING GRADED WALKING ON A SLOPE COMPARED WITH ASCENDING AND DESCENDING STAIRS

The purpose of this study was to compare the energetics of the lower extremity joints during uphill and downhill walking on slopes and stairs. 10 subjects were filmed and their ground reaction forces were measured during uphill and downhill walking on a ramp and on a staircase (24°) at the same speed. Inverse dynamics were used to calculate net joint forces and moments as well as joint power and energy at the ankle, knee and hip joint. Both, for uphill and downhill walking, the energy is more balanced in the staircase compared with the ramp conditions. Ascending stairs shifts the energy from the ankle joint to the hip joint, while in descending stairs a shift from the knee joint to the ankle joint can be observed

INFLUENCE OF BODY WEIGHT ON JOINT LOADING IN STAIR CLIMBING

Exercise is an essential treatment in childhood obesity. Due to the low impact on joint loading exercise recommendations are aerobic exercise such as swimming, cycling and walking (Hassink et al, 2008). Little is known though about the effect of adiposity on the function of the locomotor system (Wearing et al., 2006). Only limited research has been done on obese gait in children (Nantel et al. 2006) and even less is known about other weight bearing tasks such as climbing stairs. Therefore, the aim of this study was to examine the influences of obesity on the load pattern of the lower extremity joints of obese children while ascending and descending stairs

EFFECTS OF AGE, GENDER AND ACTIVITY LEVEL ON COUNTER-MOVEMENT JUMP PERFORMANCE AND VARIABILITY IN CHILDREN AND ADOLESCENTS

The aim of this study was to investigate counter-movement jump performance and variability in a large population of children and adolescents with respect to age, gender, and activity level. 1835 subjects performed three counter-movement jumps with arms akimbo on a force platform. The subjects were divided into 6 age groups and three activity level groups. Jump height and maximum rate of force development were calculated for all jumps. The best trial out of three was considered for further calculations. Variability of both parameters was indicated by the coefficient of variation over three jumps. Both parameters increased with increasing age while their variability decreased. Boys jumped higher than girls. Regarding maximum rate of force development female subjects showed higher values. The active subjects jumped higher and with less variability than the sedentary group. Jump height and maximum rate of force development are good parameters to describe the development of jumping performance regarding age, gender and activity aspects. Due to the high variability of maximum force rate development, however, this parameter has to be interpreted with caution in subject-specific assessments

RELIABILITY OF DROP JUMP VARIATIONS IN PERFORMANCE DIAGNOSTICS

In several sports athletes have to produce maximal power for accelerating the body and/or sport equipment (e.g. long jump, shot putt, basketball, etc.). The primary indicator used for estimating power output in drop jumps are the peak force rate (Fex) and the peak force (Fmax). These variables also characterise the reactive force ability of an athlete during a stretch-shortening-cycle (SSC). In order to use the accumulated energy produced in the eccentric phase during the concentric contraction, the contact please revise must not be longer than 200 ms (Komi 1984). Reactive force abilities are commonly tested in drop jumps (DJ). The accomplishment of DJ is variously described in the literature, so no standardized conditions are given (Baca 1999). One corresponding aspect is the arm position (free arm-swing vs. arms akimbo). Particularly, jumps with arm-swing require a higher grade of coordination (e.g. basketball) and are associated with an enhanced jump height. DJs with arms akimbo are often used in subjects with less sports experience or if the performance diagnostics primarily focuses on the power output in isolated leg extensions. Another aspect is the method of calculating the jump height from the measured force data. The calculation of the jump height from the momentum (based on the force-time-curve) might be inaccurate as the exact drop height is not known. Consequently, the jump height often is calculated from the flight time. This method, however, is also inaccurate if the landing position differs substantially from the take-off position. This problem might be solved performing a consecutive double DJ. Thus, the aim of the study is to investigate different DJ variations with respect to reliability

EFFECT OF SPORT ACTIVITY ON COUNTER MOVEMENT JUMP PARAMETERS IN JUVENILE STUDENTS

INTRODUCTION: The counter movement jump (CMJ) is a commonly used method in performance diagnostics to measure leg power (Frick et al., 1991). The use of arm movements during jumping can increase the release velocity and thereby the jump height (e.g. Harman et al., 1990, Gerodimos et al., 2008). Despite the consensus, that arm-swing enhances the performance in the CMJ, still disagreement exists which jumping technique (with or without arm-swing) should be used in performance diagnostics. Marcovic et al. (2004) showed a good reliability for squat jump (SJ) and CMJ without arm-swing for physical education students, who had sufficient experience in explosive activities such as jumping. In contrast, for untrained individuals both, the use and the avoidance of the arm-swing can lead to differences in the jumping performance. The fixation of the arms at the hips might be unfamiliar and might cause variability in jump height. Unskilled use of the arm-swing, however, can lead to differences in jump height (Marcovic et al., 2004). To our knowledge, limited research has been done regarding the difference in variability between the two jumping techniques (with or without arm-swing). Therefore, one aim of this study was to describe differences between these two jumping techniques under consideration of the athletic experience. Furthermore, a specific focus should be set on the variability of the different jumps for experienced (more than 6 hours sports activity a week) compared with less experienced individuals, which may give some more information about the application of these two methods to the performance diagnostics. METHODS: 380 students (12.7 ± 2.0 yrs, 47.9 ± 12.7 kg) of the secondary school category participated in this study. They were divided in two groups. The first group included athletic experienced students participating in special sports programs (more than 6 hours a week), and the second group consisted of students with less or nearly no special sports experience. All subjects were asked to perform three maximum vertical jumps while using an arm-swing (CMJA) and afterwards while holding their arms at the hip (CMJ). The instruction in both conditions was to jump as high as possible. Vertical ground reaction forces were measured with a divided force plate (“Leonardo Force Platform”, 800 Hz). Jump height (h), maximum force and coefficient of variance (cv) were calculated. t-tests and ANOVA were used for statistical analysis. RESULTS AND DISCUSSION: CMJAs show significantly greater jump heights compared to CMJ (Δh=3.3 cm ± 2.1). This corresponds with previously reported results (e.g. Harman et al., 1990, Gerodimos et al., 2008). Jump height of the experienced group was higher than the jump height of the less experienced group (CMJA: Δh=5.0 cm, CMJ: Δh=3.8 cm). The variability of the jump height is higher for CMJA compared with CMJ (Δcv=1.4% ± 5.8). The experienced group shows lower variability than the less experienced group (CMJA: Δcv=-1.8%, CMJ: Δcv= -1.0%). REFERENCES: Frick, U., Schmidtbleicher, D. and Wörn, C. (1991). Vergleich biomechanischer Meßverfahren zur Bestimmung der Sprunghöhe bei Vertikalsprüngen. Leistungssport, 2/91, 48-53. Harman, E.A., Rosenstein, M.T., Frykman, P.N. and Rosenstein, R.M. (1990). The effects of arms and countermovement on vertical jumping. Medicine and Science in Sports and Exercise, 22(6), 825-833. Gerodimos, V., Zafeiridis, A., Perkos, S., Dipla, K., Manou, V. and Kellis, S. (2008). The contribution of stretch-shortening cycle and arm-swing to vertical jumping performance in children, adolescents, and adult basketball players, Pediatric Exercise Science, 20, 379-389. Markovic, G., Dizdar, D., Jukic, I. and Cardinale, M. (2004). Reliability and factorial validity of squat and countermovement jump tests. Journal of Strength and Conditioning Research, 18(3), 551-555

LATERALITY IN VERTICAL JUMPS

Laterality is a widely investigated phenomenon in motor activities. Various studies deal with the functional dominance of one limb or one side of the body in sports (e.g. Fischer, 1988, Oberbeck, 1989). One common method for the identification of lateral differences in the lower limbs is the single-leg vertical jump (e.g. Stephens, 2005). In order to reduce the risk of injury and the coordinative demand Impellizzeri et al. (2007) and Newton et al. (2006) proposed a double-leg vertical jump force test for the assessment of bilateral strength asymmetry. The focus of these studies was set on the strength imbalance between the right and left leg using the maximum force as the relevant factor. Further parameters to describe lateral differences were neglected and still little is known about the coherence between laterality and jumping performance. Therefore, the aim of this study was to investigate laterality in established double-leg vertical jumps in performance diagnostics, such as the counter movement jump (CMJ), squat jump (SJ) and drop jump (DJ)

Does an inverted pendulum model accurately represent the gait of individuals with unilateral transfemoral amputation while walking over level ground?

Study Design: Controlled trial Background: An inverted pendulum model represents the mechanical function of able-bodied walking accurately, with centre of mass height and forward velocity data plotting as sinusoidal curves, 180 degrees out of phase. Objectives: The current study investigated whether the inverted pendulum model represented level gait in individuals with a unilateral transfemoral amputation. Methods: Kinematic and kinetic data from ten individuals with unilateral transfemoral amputation and fifteen able-bodied participants were recorded during level walking. Results: During level walking, the inverted pendulum model described able-bodied gait well throughout the gait cycle, with median relative time shifts between centre of mass height and velocity maxima and minima of between 1.2%-1.8% of gait cycle. In the group with unilateral transfemoral amputation, the relative time shift was significantly increased during the prosthetic limb initial double-limb support phase by 6.3%. Conclusion: The gait of individuals with unilateral transfemoral amputation shows deviation from a synchronous inverted pendulum model during prosthetic limb stance. The reported divergence may help explain such individuals’ increased metabolic cost of gait. Temporal divergence of inverted pendulum behaviour could potentially be utilised as a tool to assess the efficacy of prosthetic device prescription

JOINT LOADING AT DIFFERENT VARIATIONS OF SQUATS

The purpose of this study was to identify the effect of squatting in a common, in a knee-shifted position and in an inclined position (3 cm heel lift) on joint loading. 16 male subjects were tested during squatting with an additional mass of 20 kg. Kinematic and kinetic recordings were performed by two force platforms (AMTI) and a ten infrared camera system (VICON). Inverse dynamics were calculated using a recursive multibody algorithm. Results showed significantly higher ankle dorsiflexion moments as well as higher knee varus moments for the knee-shifted performance. Due to the higher load on the ankle and the knee joint the knee-shifted variation should be avoided in squat training. The inclination of 3 cm does not lead to alterations of the joint moments and therefore does not lead to beneficial effects with respect to joint loading

Joint moments during downhill and uphill walking of a person with transfemoral amputation with a hydraulic articulating and a rigid prosthetic ankle—a case study

Introduction: Functional characteristics of prosthetic ankle design may facilitate sloped walking for transfemoral amputees. The aim of the current case-study was to analyse the effects of a rigid vs. a hydraulically articulating ankle component on the biological joint moments of a transfemoral amputee during downhill, uphill and level walking. Methods: The gait of one unilateral transfemoral amputee, using the same prosthetic foot with rigid and hydraulic ankle components, was analysed and compared to a control group of 18 able-bodied participants. Kinematic and kinetic data were recorded at self-selected walking speed on a sloped ramp with inclinations of -12°, -4° (downhill), 0° (level), +4° and +12° (uphill). Results: The slope influenced lower limb joint moments similarly in both able-bodied and transfemoral participants. The effect of altering ankle movement through exchanging prosthetic ankle componentry was most acutely seen at the hip joint of the residual limb. The use of a hydraulic ankle joint component resulted in decreased mean hip joint extension and flexion moments of up to 92% and 48% respectively in the residual limb when compared to using the rigid ankle joint component, respectively. Conclusion: During sloped walking, the use of a hydraulically articulating vs. rigid ankle joint component reduced the joint moments observed at the hip joint of the residual limb in a unilateral transfemoral amputee. This indicates a benefit for transfemoral amputees as the increased ankle function reduces the moment producing requirements of the hip joint which may result in decreased energy consumption and subsequently, a more efficient gait