Doctor of Philosophy

dissertationMost cycling power is produced during leg extension with minimal power production occuring during the transition between the extension-flexion phases. A prolonged leg extension phase and reduced transition phase could increase cycling power by allowing muscles to generate power for a greater portion of the cycle. Noncircular chainrings have been designed to prolong the time spent in the powerful leg extension phase by varying crank angular velocity within the pedal cycle. The purposes of this dissertation were to evaluate the extent to which noncircular chainrings influence power, biomechanics, and metabolic cost during maximal and submaximal cycling. In the first study, I investigated the effects of chainring eccentricity (C = 1.0, R = 1.13, O = 1.24) on maximum cycling power (Pmax) and optimal pedaling rate (RPMopt). Chainring eccentricity did not influence Pmax and RPMopt. Despite reasonable theory regarding a prolonged leg extension phase and reduced transition phase, chainring eccentricity did not influence Pmax and RPMopt during maximal cycling. In the second study, I evaluated the influence of noncircular chainrings on joint-specific kinematics and power production during maximal cycling. Ankle angular velocity was significantly reduced (-13±12% and -37±13% at 90 and 120 rpm, respectively) with the O chainring, whereas knee and hip angular velocities were unaffected during the leg extension phase. Further, joint-specific power production was unaffected by chainring eccentricity. These results demonstrate that redundant degrees of freedom (DOF) in the cycling action (i.e., ankle angle) allowed cyclists to negate the effects of eccentricity and maintain their preferred hip and knee actions. In my third study, I evaluated the extent to which chainring eccentricity influenced metabolic cost and biomechanics of submaximal cycling. My study protocol allowed for separate analysis of eccentricity and pedal speed (known to influence metabolic cost). Chainring eccentricity with similarly matched pedal speeds reduced knee (-10%) and hip (-5%) angular velocities, while metabolic cost and cycling efficiency remained unaffected. Despite small but significant alterations in joint-specific kinematics, chainring eccentricity did not influence metabolic cost or cycling efficiency during submaximal cycling. Taken together, these results indicate that commercially available noncircular chainrings do not provide performance benefits over conventional circular chainrings during maximal and submaximal cycling

Principles of Neuromusculoskeletal Coordination in Human Cycling

Optimisation of movement strategies during cycling is an area which has gathered a lot of attention over the past decade. Resolutions to augment performance have involved manipulations of bicycle mechanics, including chainring geometries. Elliptical chainrings are proposed to provide a greater effective diameter during the downstroke, manipulating mechanical leverage and resulting in greater power production during this period. A review of the literature indicates that there is a pervasive gap in our understanding of how the theoretical underpinnings of elliptical chainrings might be translated to practical use. Despite reasonable theory of how these chainrings might enforce a variation in crank angular velocity and consequently alter force production, performance-based analyses have struggled to present evidence of this. The purpose of this thesis was to provide a novel approach to this problem by combining experimental data with musculoskeletal modelling and evaluating how elliptical chainrings might influence crank reactive forces, joint kinematics, muscle-tendon unit behaviour and muscle activation. One main study was proposed to execute this analysis, and an anatomically constrained model was subsequently used to determine the joint kinematics and muscle-tendon unit behaviour. Bespoke elliptical chainrings were designed for this study and as such, different levels of chainring eccentricity (i.e. ratio of major to minor axis) and positioning against the crank were presented whilst controlling the influence of other variables known to affect the neuromuscular system such as cadence and load. Findings presented in this thesis makes a new and major contribution in our understanding of the neuromusculoskeletal adaptations which occur when using elliptical chainrings, showing alterations in crank reaction force, muscle-tendon unit velocities, joint kinematics and muscle excitation over a range of cadences and loads, and provides direction for where the future of this research might be best applied

An Investigation of Kinetic Visual Biofeedback on Dynamic Stance Symmetry

The intent of the following research is to utilize task-specific, constraint-induced therapies and apply towards dynamic training for symmetrical balance. Modifications to an elliptical trainer were made to both measure weight distributions during dynamic stance as well as provide kinetic biofeedback through a man-machine interface. Following a review of the background, which includes research from several decades that are seminal to current studies, a design review is discussed to cover the design of the modified elliptical (Chapter 2). An initial study was conducted in a healthy sample population in order to determine the best visual biofeedback representation by comparing different man-machine interfaces (Chapter 3). Index of gait symmetry measures indicated that one display interface optimized participant performance during activity with the modified elliptical trainer. A second study was designed to determine the effects of manipulating the gain of the signal to encourage increased distribution towards the non-dominant weight bearing limb. The purpose of the second study was to better understand the threshold value of gain manipulation in a healthy sample set. Results analyzing percentage error as a measure of performance show that a range between 5-10% allows for a suitable threshold value to be applied for participants who have suffered a stroke. A final study was conducted to apply results/knowledge from the previous two studies to a stroke cohort to determine short-term carryover following training with the modified elliptical trainer. Data taken from force measurements on the elliptical trainer suggest that there was carryover with decreased error from pre to post training. For one participant GaitRite® data show a significant difference from pre to post measurements in single limb support. The results of the research suggest that visual biofeedback can improve symmetrical performance during dynamic patterns. For a better understanding of visual biofeedback delivery, one display representation proved to be beneficial compared to the others which resulted in improved performance. Results show that healthy human participants can minimize error with visual biofeedback and continue minimizing error until a threshold value of 10%. Finally, results have shown promise towards applying such a system for kinetic gait rehabilitation

The lower extremity kinematics and kinetics of stationary cycling in young children with and without cerebral palsy

Children with cerebral palsy (CP) are at risk of secondary changes, such as bone deformation. Physical activity is important to reduce these changes and to improve physical function, especially when children are young. Cycling is a great locomotor skill for this because it can be used in therapeutic and in recreational settings. Standardization of cycling protocols is needed to give therapists a better understanding how maximum improvements can be obtained. For this, we have to understand the biomechanics of cycling in young children with CP. We have investigated the kinematics and kinetics of cycling in young children with and without CP, and the influence of changes in task demands on these biomechanics. It was hypothesized that young typically developing (TD) children have altered biomechanics during cycling in comparison to older children and that young children with CP have alterations in comparison to TD peers. Furthermore, it was expected that spasticity reduction by botulinum toxin (BTX) treatment would improve these biomechanics in children with CP. In Study 1, it was shown that 4-year-olds TD children had more out-of-plane motion than 6-, 8- and 10-year olds, while motions in the sagittal plane were similar between groups. Also, 4-year-olds produced higher jerk cost when cycling at high cadences. In Study 2, analysis revealed that children with CP were only able to cycle at low resistance and low cadences and were less adaptable to changes in movement speed. Adjustments in joint angles, joint torques, jerk cost and pedal forces in all three planes of motion were observed, indicating that children with CP cycled less efficiently than TD peers. In Study 3, it was shown that CP-specific alterations in cycling biomechanics were reduced 3 weeks after BTX injections. This work has increased our understanding of the cycling ability of young children. It led to the conclusion that children with CP can cycle under reduced task demands in comparison to TD peers. When spasticity is reduced, the adaptability of children with CP against changes in task demands is increased. The findings of these studies help us understanding the influences of cycling in children with CP.Kinesiology and Health Educatio

Medial and Lateral Tibiofemoral Contact Forces for Individuals with High Body Mass Index in Gait and Cycling Training

The prevalence of knee osteoarthritis, a degenerative joint disease characterized by the degradation of articular cartilage, is correlated with the rise in obesity. The rising rates of obesity in children and adults highlight the need for identifying a sustainable physical activity that promotes fitness while mitigating initiation and progression of osteoarthritis. The objective of this study was to determine an effective rehabilitation and lifelong fitness sustainment exercise regimen that minimize risk of osteoarthritis in individuals with high body mass index (BMI). The aim was to examine knee medial and lateral contact forces in gait and cycling training. Gait at self-selected speeds and cycling at moderate resistance were studied using motion analysis in normal BMI and high BMI participants. Individuals with high BMI exhibited abnormal kinematics and increased kinetics in gait but neutral knee abduction-adduction angles, lower knee contact forces, and balanced mediolateral force distribution in cycling. The combination of maladaptive kinetics (excessive cartilage loading) and altered kinematics (primarily knee adduction angles) observed in gait for the high BMI cohort demonstrate the profound adverse effect of weight bearing and impact exercises on knee biomechanics. Exercise rehabilitation modalities should aim to minimize cartilage loading, correct altered knee angles, and prioritize balanced mediolateral force distributions in individuals with high BMI. Cycling, a non-weight bearing and low impact exercise, addresses all these factors because it constrains kinematic patterns with the pedals and carries significant body weight on the saddle

THE EFFECTS OF OBESITY ON RESULTANT KNEE JOINT LOADS FOR GAIT AND CYCLING

Osteoarthritis (OA) is a degenerative disease of cartilage and bone tissue and the most common form of arthritis, accounting for US$ 10.5 billion in hospital charges in 2006. Obesity (OB) has been linked to increased risk of developing knee OA due to increased knee joint loads and varus-valgus misalignment. Walking is recommended as a weight-loss activity but it may increase risk of knee OA as OB gait increases knee loads. Cycling has been proposed as an alternative weight-loss measure, however, lack of studies comparing normal weight (NW) and OB subjects in cycling and gait hinder identification of exercises that may best prevent knee OA incidence. The objective of this work is to determine if cycling is a better weight-loss exercise than gait in OB subjects as it relates to knee OA risk reduction due to decreased knee loads. A stationary bicycle was modified to measure forces and moments at the pedals in three dimensions. A pilot experiment was performed to calculate resultant knee loads during gait and cycling for NW (n = 4) and OB (n = 4) subjects. Statistical analyses were performed to compare knee loads and knee angles, and to determine statistical significance of results (p \u3c 0.05). Cycling knee loads were lower than gait knee loads for all subjects (p \u3c 0.033). OB axial knee loads were higher than NW axial knee loads in gait (p = 0.004) due to the weight-bearing nature of gait. No differences were observed in cycling knee loads between NW and OB subjects, suggesting cycling returns OB knee loads and biomechanics to normal levels. The lack of significant results in cycling could be due to the small sample size used or because rider weight is supported by the seat. Limitations to this study include small sample size, soft tissue artifact, and experimental errors in marker placement. Future studies should correct these limitations and find knee joint contact force rather than knee resultant loads using v EMG-driven experiments. In conclusion, cycling loads were lower than gait loads for NW and OB subjects suggesting cycling is a better weight-loss exercise than gait in the context of reducing knee OA risk

The Impact of Crossramp Angle and Elliptical Path Trajectory on Lower Extremity Muscle Activation

Abstract The purpose of this study was to examine the effects of linear path and converging path ellipticals at three varying crossramp angles (35°, 25°, and 15°) on mean muscle activation of the gluteus maximus (GMAX), semitendinosus (ST), vastus medialis (VM), lateral gastrocnemius (LG), and vastus lateralis (VL). The study consisted of 25 young adults (15 males and 10 females. All subjects had previous experience with elliptical trainers and had no contraindications preventing them from taking part in the study. The main outcome measure was mean muscle activation, presented at %MVC, for GMAX, ST, VM, LG, and VL. A two-way, repeated measures analysis of variance (ANOVA) was performed to determine significance, with an alpha level of 0.05. The converging path elliptical trainer showed no significant difference in muscle activation for GMAX, ST, VM, or LG, compared to the linear path elliptical, but was significantly higher (p = .006) for VL. Results for the crossramp angle showed that VM and VL had significantly higher muscle activation on the 35° ramp angle, with activation lessening from 25° to 15° (p = .027 and p \u3c .001 respectively). LG showed higher activation on the 15° ramp angle with activation lessening from 25° to 35° (p = .003). Exercising at a higher crossramp angle appears to activate the quadriceps more, while exercising at a lower crossramp angle would activate the LG to a higher degree. Additionally, individuals wanting to focus on VL activation should perform exercise on a converging path elliptical at a higher crossramp angle; however, caution should be exercised to account for over strengthening of the VL

Effects of Lateral Shoe Wedges and Toe-in Foot Progression Angles on the Biomechanics of Knee Osteoarthritis during Stationary Cycling

Exercise is important for individuals with knee osteoarthritis (OA) but certain activities can be painful and discourage participation. Cycling is commonly prescribed for OA but practically no previous literature exists. Due to their altered knee kinematics, OA patients may be at greater risk of OA progression or other knee injuries during cycling. The purpose of Study One was to investigate the effects of lateral wedges on knee joint biomechanics and pain in patients with medial compartment knee OA. The purpose of Study Two was to investigate the effects of toe-in foot progression angles on the same variables. Thirteen OA subjects and 11 healthy subjects participated. A motion analysis system and custom instrumented pedal was used to collect 5 pedal cycles of kinematics and kinetics during 2 minutes of cycling in one neutral and two lateral wedge conditions (5° and 10°) for Study One and 2 toe-in conditions (5° and 10°) for Study Two. Subjects pedaled at 60 RPM and 80 watts and rated their knee pain on a visual analog scale. Study One: There was a 22% decrease in the knee abduction moment with the 10° wedge. This finding was not accompanied by a decrease in knee adduction angle or pain. Additionally, there was an increase in vertical and horizontal PRF which may negate the advantages of the decreased KAM. Study Two: For the OA subjects, there was a 61% (2.7°) and a 73% (3.2°) decrease in peak knee adduction angle compared to neutral. This finding was not accompanied by a decrease in pain or KAM because of high inter-subject variability. A simple linear regression showed a positive correlation between Kelgren-Lawrence (K/L) score and both peak knee adduction angle and KAM. For OA patients, cycling with a 10° lateral wedge or a decreased foot progression angle may be beneficial in slowing the progression of OA or minimizing other knee injuries. Patients with a higher K/L score may have greater risk of injury. More research is needed to investigate the joint contact forces as well as long term effects of riding with wedges or toe-in foot angles

Efficacy of a Cycling Intervention with Pedal Reaction Force Augmented Feedback on Reducing Inter-Limb Asymmetries in Patients with Unilateral Total Knee Arthroplasty

Fifteen patients with unilateral total knee arthroplasty (TKA) performed cycling at two workates (80 W and 100 W) and two walking conditions (preferred and fast speeds). Ten of these patients of TKA also participated in a short-term cycling intervention paired with visual augmented feedback of vertical pedal reaction forces for six sessions over two-three weeks. These ten patients of TKA participated in a 2nd post-training testing session. Study One compared the knee joint biomechanics for all fifteen participants during stationary cycling to ascertain if any biomechanical asymmetries may be present. The replaced limbs displayed significantly lower peak knee extension moment (KEM) and vertical pedal reaction (PRF) compared to non-replaced limbs during stationary cycling. Study Two examined the effect of the short-term cycling intervention on the knee joint biomechanics and biomechanical asymmetries during stationary cycling for the selected ten patients of TKA. The short-term cycling intervention had no significant effect for peak KEM or vertical PRF asymmetries during stationary cycling. Peak KEM asymmetries did decrease by 10% and 9.9% at 80 W and 100 W, respectively. Study Three examined the effect of the short-term cycling intervention on the knee joint biomechanics and biomechanical asymmetries during gait. Similarly, the short-term cycling intervention had no effect on peak KEM asymmetries and vertical ground reaction force (GRF) asymmetries during both walking condition. Study Four compared the estimated tibiofemoral joint forces during stationary cycling between the replaced and non-replaced limbs of the fifteen patients of TKA. The replaced limbs also had lower medical tibiofemoral contact force (MCF) compared to the non-replaced limbs during stationary cycling at 80 W. The non-replaced limb had greater peak MCF compared to the lateral tibiofemoral contact force (LCF). Unilateral TKA patients cycling with similar reductions of KEM in their replaced limbs. During cycling, there was no difference between MCF and LCF for the replaced limbs, potentially indicating a successful operation to restore knee joint alignment. In summary, the use of a short-term cycling intervention with augmented feedback for six sessions were not significantly beneficial for addressing KEM asymmetries in both cycling and gait. However, the 10% reductions of peak KEM asymmetries may indicate some clinical benefits of this intervention. Future studies should examine similar interventions with an increased number of training sessions

The Influence of Musculoskeletal Geometry on the Metabolic Cost of Pedaling

The human musculoskeletal system consists of several muscles crossing each joint. In the human lower limb, most major muscles cross either one or two joints; labeled as uniarticular or biarticular muscles, respectively. The major biarticular muscles of the leg are the rectus femoris, hamstrings, and gastrocnemius. Several suggestions have been proposed as to how biarticular muscles may reduce the metabolic cost of human movement. Using experimental protocols, it is difficult to address the energetic effects of biarticular muscles, as individual muscle contributions to human movement cannot be measured and there is no way to determine what the effect might be on the energetics of movement if instead of a biarticular muscle there were two equivalent uniarticular muscles. Therefore, this project used a musculoskeletal modeling approach to address the question of whether biarticular muscles reduce the metabolic cost of submaximal pedaling. We used one standard model representing a simplified human musculoskeletal design with 6 uniarticular and 3 biarticular muscles and created three different models, each replacing one biarticular muscle of the standard model with two mechanically equivalent muscles. The models with the altered musculoskeletal design could not be expected to pedal in the same manner as a human, so it was not possible to generate simulations of pedaling by tracking experimental pedaling data, a proven method for replicating submaximal pedaling computationally. Therefore, in the first study, we tested the ability of five performance-based criterion to generate predictive simulations of submaximal pedaling using the standard model. We found that minimizing muscle activations best replicated the general kinematics, kinetics and muscle excitation patterns of submaximal pedaling. In the second study, we used this performance-based criterion to generate pedaling simulations for the three new musculoskeletal models with the replaced biarticular muscles. All three new musculoskeletal designs predicted greater metabolic cost than the standard model. Analyzing the mechanisms proposed in the literature by which biarticular muscles might yield energy savings did not reveal a general cause for the increases. We conclude that the greater metabolic costs likely resulted from unique coordination patterns adopted by the altered musculoskeletal designs to meet the task demands of pedaling