Effects of Aging on Patellofemoral Joint Stress During Stair Negotiation on Challenging Surfaces

Introduction: Patellofemoral pain is an incessant lower limb musculoskeletal disorder that may be underreported in older adults. During common locomotor activities, such as when negotiating stairs, older adults (over the age of 65 years) adopt knee biomechanics reported to increase patellofemoral pain. Negotiating stairs with a challenging surface, such as uneven or slick, may place greater demand on the knee and further exacerbate joint biomechanics related to PFJ stress. Yet, it is unknown if older adults exhibit increases in patellofemoral joint (PFJ) stress when negotiating stairs with challenging surfaces. Purpose: The purpose of this study was to examine the effect of age (young and older adults) and surface (normal, slick, and uneven) on the magnitude and temporal waveform of patellofemoral joint stress during stair ascent and descent tasks. Methods: Two cohorts (12 young: ages 18-25 years; 12 older: over 65 years) had knee biomechanics quantified after they ascended and descended 18.5 cm stairs on normal, slick, and uneven surfaces at a self-selected speed. Statistical Analysis: Peak of stance (0-100%) PFJ stress and associated components (including PFJ reaction force and contact area, and knee flexion angle and moment) were submitted to a two-way RM ANOVA to test the main effects of and interaction between age (young vs old) and surface (normal, slick, and uneven). A statistical parametric mapping two-way ANOVA was used to determine main effects of and interaction between age and surface for the PFJ stress waveform. Results: During the stair ascent, older adults exhibited greater PFJ stress from 56 to 84% of stance (p \u3c 0.001), which may be attributed to the greater PFJ stress-time integral (p = 0.004) and later peak PFJ stress (p = 0.024) compared to young adults. Additionally, a significant age by surface interaction was observed for time of peak PFJ stress (p = 0.041) during stair ascent, where older adults exhibited a later peak PFJ stress compared to young adults (p = 0.008), and later peak PFJ stress compared to normal and slick surface (both: p = 0.014). Surface impacted PFJ stress waveform (all: p \u3c 0.001), but not magnitude (p \u3e 0.05) during both stair ascent and descent. During stair ascent on the uneven surface, participants exhibited smaller PFJ stress from 8 to 25% of stance compared to normal surface, but greater PFJ stress from 57 to 90% and 49 to 77% of stance compared to the normal and slick surfaces (all: p \u3c 0.001). On the uneven surface, participants exhibited a greater PFJ stress-time integral (both: p = 0.010) compared to the normal and slick surfaces. During stair descent, on the uneven surface, participants only exhibited greater PFJ stress-time integral (p = 0.017) compared to slick surface, while PFJ stress was smaller from 5 to 18% of stance, but greater stress from 92 to 99% of stance (both: p \u3c 0.001) on the slick compared to the normal surface. Conclusion: Older adults are more likely to exhibit knee biomechanics related to PFJ pain development when navigating stairs. Specifically, the larger, later PFJ stress exhibited by older adults when ascending, but not descending the stairs may increase loading of the joint’s articular cartilage and increase risk of developing PFJ pain. Yet, all participants exhibited alterations in knee biomechanics that may lead to greater PFJ stress when negotiating stairs with slick and uneven surfaces

Adaptations in plantarflexor muscle-tendon properties and their impact on gait in claudicants with peripheral arterial disease

Peripheral arterial disease (PAD) is a chronic atherosclerotic disease, primarily affecting the lower limbs. The associated intermittent claudication (IC) is a muscle pain/cramping sensation in the legs, primarily brought on by physical activity, such as walking, which can negatively affect daily function and quality of life. Poorer levels of lower-limb muscle strength are strong predictors for mortality and the plantarflexor muscles in particular are a frequent site of claudication pain, with previous literature also indicating their dysfunction during level gait. However, little is known about the size and architecture of these muscles, the quality of the in-series Achilles tendon or the factors that contribute to voluntary joint moments and how these relate to physical function in this population. The aim of this thesis was to determine the functional properties of the gastrocnemii muscles and Achilles tendon in order to make evidence-based clinical recommendations for specific exercise interventions for claudicants.A total of 23 participants (13 claudicants and 10 controls) took part in the study. Muscle-tendon dimensions and architecture, tendon properties, activation patterns and muscle strength, power and quality (specific tension) were assessed be integrating ultrasound imaging, electromyography and dynamometry. Stair gait biomechanics were analysed using 3D motion capture as indicators of whole body physical function. Within the claudicant cohort, disease severity was determined using the ankle brachial pressure index and walking performance assessed by a modified six-minute walk test. Average post-exercise ankle brachial pressure index of the claudicating-limbs were 0.55±0.21 with initial (onset of claudication pain) and absolute (maximal claudication pain) walking distances of 105±45m and 265±136m, respectively.The first study investigated the relationships between the resting architecture of the gastrocnemii and functional properties of the Achilles tendon with disease severity and walking endurance. Worse disease severity was significantly associated with longer fascicle: tendon length ratios in both lateral (R=-.789, P=.001) and medial (R=-.828, P=<.001) gastrocnemius, and increased tendon hysteresis (R=-.740, P=.006). This suggests that the Achilles tendon has undergone deleterious changes and the muscle has adopted a structure designed to compensate for this. However, the concomitant associations with poorer walking endurance indicate this mechanism is not effective. Walking endurance could also be explained by lateral and medial gastrocnemius pennation angle, maximum tendon force, tendon hysteresis and disease severity (R2=~0.6). The direction of coefficients within these models suggests that improving tendon properties and increasing strength, but without increasing pennation angle, would be beneficial for walking endurance. Thus, eccentric resistance training may be an effective exercise intervention.The second study investigated relationships between static and dynamic muscle quality with disease severity and walking endurance. The power-producing capabilities of claudicants’ plantarflexors (both the claudicating/painful limb and asymptomatic limb) were impaired compared to healthy controls, particularly at high contraction velocities (24% difference at 180°/s). This could be explained by some reduction in gastrocnemii muscle quality and a greater reliance on the prominently type I fibred soleus muscle. As reduced dynamic capability of the plantarflexor muscles was associated with disease severity (R=.541, P=.037) and walking endurance (R=.689, P=.006), high velocity resistance training of the plantarflexor muscles appears important to maintain functional performance.The third and fourth studies investigated the functionally challenging daily tasks of stair ascent and stair descent, respectively. During stair ascent, plantarflexor moments were similar in claudicants compared to healthy controls, indicating the muscle could meet the strength demands of this task. We also observed that ankle angular velocity at the instant of peak moment, peak ankle power generation, as well as propulsive and vertical forces, were all reduced during forward continuance in the claudicating-limb group. It seems that claudicants possess adequate levels of strength when moving more slowly but are unable to remain strong when moving more quickly, therefore it could be suggested that the slower walking speed is a means to allow claudicants to operate within safer limits relative to their maximal strength capacity. This provides further evidence, in a functional context, of the velocity-dependent limitations of the plantarflexors detected in study two. During stair descent we hypothesised that the task demands would be redistributed away from the affected plantarflexors towards the muscles surrounding the hips and knees. Instead, the claudicants placed a greater reliance on the plantarflexors compared to healthy controls (40% vs 28% of plantarflexor contribution to peak support moment). Additionally, a unique hip extensor strategy was exposed during weight acceptance that was adopted by 73% of the claudicating-limb group, which was also associated with increased disease severity. However this was not a mechanism to reduce the functional demands on the plantarflexors but rather to reduce demands on the knee musculature. These data indicate the claudicants were relying heavily on the functionally limited plantarflexors to absorb the falling body mass during weight acceptance in stair descent, which may pose an increased risk of falling.This thesis has identified important changes in the structure and quality of the gastrocnemii muscles and the properties and function of the Achilles tendon, that appear to influence whole body function during demanding and risky physical activities (stair negotiation) that necessitate alternate strategies. Taken as a whole, it is clear that high-velocity and eccentric resistance training would likely improve the musculoskeletal characteristics of claudicants, increase walking endurance and facilitate safe stair negotiation

A biomechanical approach to prevent falls in ergonomic settings

Introduction: Fall-related injuries are exceptionally prevalent in occupational settings. While endangering the workers’ health, falls cause poor productivity and increased economic burden in the workplace. Hence, identifying these threats and training workers to achieve proper postural control is crucial. Purpose: Study 1: To investigate the ankle joint kinematics in unexpected and expected trip responses during single-tasking (ST), dual-tasking (DT), and triple-tasking (TT), before and after a physically fatiguing exercise. Study 2: To investigate the impact of virtual heights, DT, and training on static postural stability and cognitive processing. Methods: Study 1: Twenty collegiate volunteers (10 males and females, one left leg dominant, age 20.35 plus-minus 1.04 years, height 174.83 plus-minus 9.03 cm, mass 73.88 plus-minus 15.55 kg) were recruited. Ankle joint kinematics were recorded while treadmill walking during normal gait (NG), unexpected trip (UT), and expected trip (ET) perturbations with DT and physical fatigue. Study 2: Twenty-eight collegiate volunteers (14 males and females; all right leg dominant; age 20.48 plus-minus 1.26 years; height 172.67 plus-minus 6.66 cm; mass 69.52 plus-minus 13.78 kg; body mass index 23.32 plus-minus 3.54 kg/m2) were recruited. They were exposed to different virtual environments (VEs) over three days with and without DT. Postural sway parameters, lower extremity muscle activity, heart rate, and subjective anxiety parameters were collected. Results: Study 1: Greater maximum ankle angles were observed during UT compared to NG, MDT compared to ST, and TT compared to ST, while greater minimum ankle angles were observed during ET compared to NG and during post-fatigue compared to pre-fatigue. Study 2: Greater postural decrements and poor cognitive processing were observed in high altitudes and DT. Discussion & conclusions: Study 1: Trip recovery responses are different between during DT, TT, and fatigue. Study 2: Static postural stability deteriorates at higher virtual altitudes and with DT, while it improves with a two-day training. Virtual height exposure reduces cognitive performance. Importance: The findings of these studies will provide insights into the biomechanics of falls in ergonomic settings and aid in designing functional and convenient fall prevention programs

THE VARIATION IN STRENGTH DECREMENT OF LOWER EXTREMITY MUSCLE GROUPS AND BIOMECHANICAL PLASTICITY IN OLDER ADULTS

Age-associated biomechanical plasticity (BP) has been established as the distal to proximal shift of joint mechanical output in old adults while walking. The cause of BP is still unknown, but changes in muscle strength of the lower extremities due to age are thought to be one of the underlying causes of BP. Old adults who had overall weaker lower extremities have been shown to have increased BP while walking on level and incline surfaces, however individual muscle groups have not yet been evaluated. We hypothesize that one causal factor of BP with age is that hip extensor muscles are more similar in strength in young and old adults than are ankle plantarflexor muscles, thus enabling old adults to walk with larger mechanical contributions from hip muscles as compensation for reduced contributions from ankle muscles. The purposes of the study were 1) compare muscle strengths of hip extensors and ankle plantarflexors between young and old adults, 2) verify BP in old adults by comparing hip and ankle joint torques and powers between age groups in level and incline walking & 3) examine the relationship between the relative strength in hip vs ankle muscles and the magnitude of BP in old adults during these gaits. 14 young (20yrs) and 22 old (76yrs) adults performed maximal isometric and isokinetic standing hip extension (20° of hip flexion) and seated ankle plantarflexion (15° of dorsiflexion). Age-based comparisons of muscle strength were made with 2X3 factor repeated measures ANOVAs, p<0.05. The same participants performed incline and level walking while ground reaction forces and 3D kinematics were obtained data. Walking joint torques and powers were calculated with inverse dynamics and were assessed using peak hip-to-ankle ratios with larger ratios indicating a larger shift of mechanical output to the hip. 2X2 factor repeated measures ANOVAs (p<0.05) for level and incline conditions were used to compare the torque and power ratios between age groups, with significant differences indicating BP. Pearson's correlations (p<0.05) were used to examine the relationship between walking power/torque ratios and the ratio of hip to ankle muscle strength in old adults. Old adults' hip extensor and ankle plantarflexor muscles were significantly weaker than young by 20% and 39%, (p<0.05). Old adults displayed a significant increase in hip/ankle ratios for both torque and power during level and incline conditions, indicating that the old adults exhibited BP (p<0.05). However, the correlations between ratios of hip and ankle isometric strength and hip/ankle peak torque and power were not significant for either level or incline walking. These findings suggest that there is a variation in strength decrement of individual lower extremities muscle groups due to age which may partially cause BP with age. However, we were unable to identify a relationship between the hip/ankle muscle strength ratio and BP, indicating the possibility of multiple factors contributing to BP