The Effect Of Hip Position/Configuration On EMG Patterns In Cycling

From the results of previous investigations examining the effect of changes in hip angles on cycling performance, it had been concluded that there is an optimal hip position/configuration which maximizes aerobic and anaerobic work. But why and how this hip position/configuration affects cycling perfonnance is unknown. Therefore, it was the purpose of this investigation to determine whether differences in cycling performance with changes in hip position/configurations are reflected and can be explaincd by changes in EMG patterns. Five male recreational cyclists were tested in 5 different hip position/configuration (0,25,50,75, and 100 degrees), as defined by the angie formed between the bicycle seat tube and a vertical line (perpendicular to the ground) passing through the pedal axis. By rotating the seat to maintain a backrest perpendicular to the ground, a systematic decrease in hip angle from the 0 to 100 degree position was induced. For each condition, the seat to pedal distance was adjusted to remain 100% (to within 3/4 inch or 1.905 cm) of the total leg length, as measured from the greater trochanter of the femur of the right leg to the ground. In each position, the minimum and maximum hip, knee, and ankle angles were obtained for one complete pedal revolution. A cycle ergometer was used with a resistance of 65 gm/kg of the subject'S body mass (3.82 joules/pedal rev/kg BM) at a pedaling frequency of 60 rpm. Each subject was strapped to the seat-backrest at the waist and hips, and pedal toeclips were worn. For each test condition, EMG activity of 6 muscle groups of the right limb were each collected at a rate of 2000 Hz with surface electrodes. A recorder and a micro-switch interfaced to a microcomputer was used to record EMG activity and pedal position. For a complete pedal cycle in each hip position, a waveform data analysis program was used to determine: (l) the sequence of activity by the different muscle groups; (2) the duration of activity; and (3) the pedal position each muscle group was active and inactive. ReANOVA's and post-hoc tests revealed significant differences in the pedal position location that the rectus femoris, gluteus maximus, vastus medialis and biceps femoris were active and inactive during a pedal cycle with changes in hip position/configuration. With a systematic change in hip position from 0 to 100 degrees, there is a backward shift in pedal position loca tion that the muscles were active and inactive. It was concluded that differences in cycling performance with changes in hip position/configuration are reflected and can be explained by differences in EMG patterns. Supported by a grant-in-aid of research from Sigma XI, The Scientific Research Society

THE EFFECT OF PEDAL CRANKARM LENGTH ON POWER PRODUCTION IN RECUMBENT CYCLE ERGOMETRY

In human powered vehicles, adjustments in seat-to-pedal distance, seat tube angle, and body orientation (trunk angle with respect to the ground) will result in changes in hip, knee, and ankle angles. Changes in these joint angles often affect cycling performance by altering muscle length, moment arm length, angle of pull, joint range of motion, and/or the force/torque/power generated by different muscle groups. How changes in crankarm length affect joint kinematics and cycling performance has not been examined. Therefore, the purpose of this investigation was to determine the effect of changes in pedal crankarm length on joint kinematics and power production in recumbent cycle ergometry. Twenty healthy volunteer male subjects (mean age = 24.8 yrs, SD = 4.4 yrs) were tested in five pedal crankarm length (1 10, 145,180,230, and 265 mm) according to a randomized sequence (with a minimum of 24 hours rest between test sessions), using a free weight Monark bicycle ergometer (Model 814E). A variable seating apparatus was constructed and used, with the seat-to-pedal distance adjusted to 100% of each subject's leg length (as measured from the greater trochanter of the right leg to the ground). Pedal toe-clips were worn, and each subject's upper body was kept perpendicular to the ground. In each condition, the minimum and maximum hip, knee, and ankle angles were measured for one complete pedal revolution. A computerized 30 second Wingate anaerobic cycling test was used, with a resistance of 85 gm/kg of each subject's body mass (5.0 joules/pedal rev/kg BM). Peak power (5 sec) and mean power (30 sec) were determined by a SMI Power Program (Sports Medicine Industries). DM MANOVAs and post-hoc tests revealed that (1) hip, knee and ankle angles changed significantly with changes in crankarm length (p < .01); (2) peak power in the 110 and 145 mm crankarm lengths were significantly greater than that in the other lengths (p < .05); and (3) mean power in the 180 mm crankarrn length was significantly greater than that in the 1 10, 230 and 265 mm condition (p < .05). With increasing crankarm lengths, there is decrement in mean joint angles (hip, knee, and ankle), an increment in joint range of motion, a decrement in peak power, and a curvilinear end in mean power. Changes in pedal crankarm length by 35 mm will significantly alter joint kinematics to affect cycling performance, as evidenced by changes in peak and mean power. The shortest crankarrn length (1 10 mm) resulted in the largest peak power production (and fatigue index), whereas the middle crankarm length (180 mm) resulted in the largest mean power production. It was concluded that the optimal crankarm length to maximize performance in recumbent cycle ergometry will be dependent on the goal of the activity. - This research was supported by a grant from the UNLV Research Grants and Fellowship Committee

The Effect of Pedal Crank Arm Length on Lower Limb Joint Angles in an Upright Cycling Position

The purpose of this investigation was to determine whether changes in CAL resulted in significant changes in joint angles, and how these changes are related to changes in cycling performance

Optimization of the Seating Position in a Human-Powered Vehicle

Until recently, most of the human-powered vehicles (HPV) were designed focusing solely on its aerodynamics characteristic. In many of these HPV designs, the rider seating position was arbitrarily chosen without consideration of its effect on the rider\u27s comfort and cycling effectiveness. Also, there is no guarantee that the seating position is related to maximum power output. Too (1991) used an experimental approach to determine that the rider will produce the maximum anaerobic power when the seat tube angle of a bicycle is at 75° whereas Hull and Gonzalez (1990) used an engineering approach to optimize the cycling biomechanics. However several factors. including aerodynamic effects, were not considered in both studies. The objective of this study was, therefore, to find the optimal rider\u27s seating position in HPV for either aerobic or anaerobic performance. The method is based on modeling a mechanism equivalent to the hip, knee, and ankle joints. All physical constraints on the motion of these three joints as well as the HPV design constraints are mathematically described. Nonlinear programming techniques were used to reach an optimal solution for either aerobic or anaerobic designs. To test the validity of the model, it was compared to the experimental results of the anaerobic cycling power test presented by Too (1991)

Visual Perception of Biomechanical Characteristics of Walking, Jumping, and Landing

Visual perception of biological systems is one important aspect which has been considered by researchers in understanding human motion. The term «biological motion» was used by Johansson (1971, 1973) to distinguish human movement patterns from the motion of rigid inanimate objects previously utilized in visual motion perception. The emphasis, however, has been on the need for distinguishing three types of motion to describe perceived kinematic relations: the relative motion of elements to each other in the configuration, the common motion of the whole configuration relative to the observer, and the absolute motion of each element in dynamic display [Cutting and Proffitt (1982)]. Based on data collected using a video-recorder, reflective tape and high powered light for producingpoint-light displays, Cutting and Proffitt (1982) concluded that relative motion is automatically minimized by the visual system. Moreover, Johansson (1971, 1973) showed that all movement pattern of walking and running can be visually identified by observers without seeing the total picture. Using a similar technique, observers were able to visually recognize gender and friends by their walking patterns (Cutting and Kozlowzki, 1977; Cutting, 1978), ones' own identity (Beardsworth and Buckner, 1981), the weight of lifted objects (Runeson and Frykholm, 1983), and to the extent that evaluation of technical skill execution was sucessfully judged (Scully, 1986). Based on the principle that relative motion is automatically minimized by the visual system, Johansson (1973), concluded that previous learning of motion patterns do not determine the perception of walking. An important factor, however, is a highly mechanical, automatic type of visual data treatment. In addition, Runeson and Frykholm (1981) stated that the dynamic variable of the event (weight of the box), is well specified in the kinematic pattern and hence the visual system is efficient in picking up such information. Identifying cues by visual information may not be sufficient, however, to distinguish discrete skills (ie., jumping and landing) and/or continuous skills (ie., walking), especially, if the direction of the movement is reversed and if the total picture is seen as an absolute motion which includes the relative and common motion (Cutting and Proffitt, 1982). Therefore, this study was conducted to test the hypotheses that experience and familiarity are important factors in visual perception of kinematic patterns and that kinetics cannot be determined effectively by observation of kinematics. The purpose of this study is to determine: (1) the ability to visually perceive differences between a continuous skill (walking forward vs. backwards): (2) a discrete skill (jumping vs. landing); (3) the actual kinetic differences in the movement; and (4) whether individuals can distinguish between movement patterns, despite the kinetic differences, while the true pattern is reversed

Optimization Of The Seating Position In A Human-Powered Vehicle

An aerobic and an anaerobic designs for a human-powered vehicle (HPV) are considered. In both cases the rider's seating position is an important design factor for either maximizing the vehicle's speed or minimizing the rider's energy requirement. The rider's seating position affects not only the aerodynamic performance of the vehicle, but more importantly the rider's physical performance. The goal of this study is to use optimization methods to improve the HPV design. The paper starts by deriving equation for torque produced by the hip and knee joints during pedaling. These equations include inertial and gravity effects. In the aerobic design the objective function is to reduce both the average and maximum variation of the torques on the hip and knee joints. In the anaerobic design, the objective function is to maximize the average of the torques on the hip and knee joints. Hip and joint torques are function of the vehicle's speed and the aerodynamic coefficient as well as the road conditions. The design variables are: 1. the seat inclination angle 2. the seat to pedal angle 3. the seat to pedal distance 4. the crank length. The search for optimal solution in both cases is constrained by: 1. the motion limits of hip and knee joints 2. conditions to ensure that the seat to crank position results in full rotation of the crank. 3. visibility of the road that limits how far the seat can be inclined for safe driving. The results have been verified by comparing it to the experimental data of Too [ 1991] for maximum anaerobic performance of a stationary bike. Both experimental and analytical techniques produced close values of the seat to pedal angles

Psychosocial job characteristics and mental health: Do associations differ by migrant status in an Australian working population sample?

Migrant workers may experience higher burdens of occupational injury and illness compared to native-born workers, which may be due to the differential exposure to occupational hazards, differential vulnerability to exposure-associated health impacts, or both. This study aims to assess if the relationships between psychosocial job characteristics and mental health vary by migrant status in Australia (differential vulnerability). A total of 8969 persons from wave 14 (2014&ndash;2015) of the Household Income and Labour Dynamics in Australia Survey were included in the analysis. Psychosocial job characteristics included skill discretion, decision authority and job insecurity. Mental health was assessed via a Mental Health Inventory-5 score (MHI-5), with a higher score indicating better mental health. Migrant status was defined by (i) country of birth (COB), (ii) the combination of COB and English/Non-English dominant language of COB and (iii) the combination of COB and years since arrival in Australia. Data were analysed using linear regression, adjusting for gender, age and educational attainment. Migrant status was analysed as an effect modifier of the relationships between psychosocial job characteristics and mental health. Skill discretion and decision authority were positively associated with the MHI-5 score while job insecurity was negatively associated with the MHI-5 score. We found no statistical evidence of migrant status acting as an effect modifier of the psychosocial job characteristic―MHI-5 relationships. With respect to psychosocial job characteristic―mental health relationships, these results suggest that differential exposure to job stressors is a more important mechanism than differential vulnerability for generating occupational health inequities between migrants and native-born workers in Australia

Lethal Mutagenesis of Poliovirus Mediated by a Mutagenic Pyrimidine Analogue

Lethal mutagenesis is the mechanism of action of ribavirin against poliovirus (PV) and numerous other RNA viruses. However, there is still considerable debate regarding the mechanism of action of ribavirin against a variety of RNA viruses. Here we show by using T7 RNA polymerase mediated production of PV genomic RNA, PV polymerase-catalyzed primer extension and cell-free PV synthesis that a pyrimidine ribonucleoside triphosphate analogue (rPTP) with ambiguous basepairing capacity is an efficient mutagen of the PV genome. The in vitro incorporation properties of rPTP are superior to ribavirin triphosphate. We observed a log-linear relationship between virus titer reduction and the number of rPMP molecules incorporated. A PV genome encoding a high-fidelity polymerase was more sensitive to rPMP incorporation, consistent with diminished mutational robustness of high-fidelity PV. The nucleoside (rP) did not exhibit antiviral activity in cell culture owing to the inability of rP to be converted to rPMP by cellular nucleotide kinases. rP was also a poor substrate for herpes simplex virus thymidine kinase. The block to nucleoside phosphorylation could be bypassed by treatment with the P nucleobase, which exhibited both antiviral activity and mutagenesis, presumably a reflection of rP nucleotide formation by a nucleotide salvage pathway. These studies provide additional support for lethal mutagenesis as an antiviral strategy, suggest that rPMP prodrugs may be highly efficacious antiviral agents, and provide a new tool to determine the sensitivity of RNA virus genomes to mutagenesis as well as interrogation of the impact of mutational load on the population dynamics of these viruses

Lethal Mutagenesis of Picornaviruses with N-6-Modified Purine Nucleoside Analogues

RNA viruses exhibit extraordinarily high mutation rates during genome replication. Nonnatural ribonucleosides that can increase the mutation rate of RNA viruses by acting as ambiguous substrates during replication have been explored as antiviral agents acting through lethal mutagenesis. We have synthesized novel N-6-substituted purine analogues with ambiguous incorporation characteristics due to tautomerization of the nucleobase. The most potent of these analogues reduced the titer of poliovirus (PV) and coxsackievirus (CVB3) over 1,000-fold during a single passage in HeLa cell culture, with an increase in transition mutation frequency up to 65-fold. Kinetic analysis of incorporation by the PV polymerase indicated that these analogues were templated ambiguously with increased efficiency compared to the known mutagenic nucleoside ribavirin. Notably, these nucleosides were not efficient substrates for cellular ribonucleotide reductase in vitro, suggesting that conversion to the deoxyriboucleoside may be hindered, potentially limiting genetic damage to the host cell. Furthermore, a high-fidelity PV variant (G64S) displayed resistance to the antiviral effect and mutagenic potential of these analogues. These purine nucleoside analogues represent promising lead compounds in the development of clinically useful antiviral therapies based on the strategy of lethal mutagenesis