Rami Hashish

The biomechanical demands of standing yoga poses in seniors: The Yoga empowers seniors study (YESS).

BackgroundThe number of older adults participating in yoga has increased dramatically in recent years; yet, the physical demands associated with yoga performance have not been reported. The primary aim of the Yoga Empowers Seniors Study (YESS) was to use biomechanical methods to quantify the physical demands associated with the performance of 7 commonly-practiced standing yoga poses in older adults.Methods20 ambulatory older adults (70.7 + − 3.8 yrs) attended 2 weekly 60-minute Hatha yoga classes for 32 weeks. The lower-extremity net joint moments of force (JMOFs), were obtained during the performance of the following poses: Chair, Wall Plank, Tree, Warrior II, Side Stretch, Crescent, and One-Legged Balance. Repeated-measure ANOVA and Tukey’s post-hoc tests were used to identify differences in JMOFs among the poses. Electromyographic analysis was used to support the JMOF findings.ResultsThere was a significant main effect for pose, at the ankle, knee and hip, in the frontal and sagittal planes (p = 0.00 – 0.03). The Crescent, Chair, Warrior II, and One-legged Balance poses generated the greatest average support moments. Side Stretch generated the greatest average hip extensor and knee flexor JMOFs. Crescent placed the highest demands on the hip flexors and knee extensors. All of the poses produced ankle plantar-flexor JMOFs. In the frontal plane, the Tree generated the greatest average hip and knee abductor JMOFs; whereas Warrior II generated the greatest average hip and knee adductor JMOFs. Warrior II and One-legged Balance induced the largest average ankle evertor and invertor JMOFs, respectively. The electromyographic findings were consistent with the JMOF results.ConclusionsMusculoskeletal demand varied significantly across the different poses. These findings may be used to guide the design of evidence-based yoga interventions that address individual-specific training and rehabilitation goals in seniors.Clinical trial registrationThis study is registered with NIH Clinicaltrials.gov #NCT 01411059

Lower limb dynamics vary in shod runners who acutely transition to barefoot running

Relative to traditional shod rear-foot strike (RFS) running, habituated barefoot running is associated with a forefoot-strike (FFS) and lower loading rates. Accordingly, barefoot running has been purported to reduce lower-extremity injury risk. Investigations, however, indicate that novice barefoot runners may not innately adopt a FFS. Therefore, the purpose of this study was to examine lower-extremity dynamics of habitually shod runners who acutely transition to barefoot running. 22 recreational RFS runners were included in this investigation. This laboratory controlled study consisted of two visits one-week apart, examining habitually shod, then novice barefoot running. Foot-strike patterns and loading rates were determined using motion analysis and force plates, and joint energy absorption was calculated using inverse dynamics. Of the 22 runners, 8 maintained a RFS, 9 adopted a MFS, and 5 adopted a FFS during novice barefoot running. All runners demonstrated a reduction in knee energy absorption when running barefoot; MFS and FFS runners also demonstrated a significant increase in ankle energy absorption. Runners who maintained a RFS presented with loading rates significantly higher than traditional shoe running, whereas FFS runners demonstrated a significant reduction in loading rate. Mid-foot strikers did not demonstrate a significant change in loading rate. These results indicate that habitually shod RFS runners demonstrate a variety of foot-strike and lower-extremity dynamic responses during the acute transition to barefoot running. Accordingly, explicit instruction regarding foot-strike patterns may be necessary if transitioning to barefoot. Long-term prospective studies are required in order to determine the influence of FFS barefoot running on injury rates.

A comparison of dorsal and heel plate foot tracking methods on lower extremity dynamics

The primary method to model ankle motion during inverse dynamic calculations of the lower limb is through the use of skin-mounted markers, with the foot modeled as a rigid segment. Motion of the foot is often tracked via the use of a marker cluster triad on either the dorsum, or heel, of the foot/shoe. The purpose of this investigation was to evaluate differences in calculated lower extremity dynamics during the stance phase of gait between these two tracking techniques. In an analysis of 7 subjects, it was found that sagittal ankle angles and sagittal ankle, hip and knee moments were strongly correlated between the two conditions, however, there was a significant difference in peak ankle plantar flexion and dorsiflexion angles. Frontal ankle angles were only moderately correlated and there was a significant difference in peak ankle eversion and inversion, resulting in moderate correlations in frontal plane moments and a significant difference in peak hip adductor moments. We demonstrate that the technique used to track the foot is an important consideration in interpreting lower extremity dynamics for clinical and research purposes.

Physical Demand Profiles of Hatha Yoga Postures Performed by Older Adults

Understanding the physical demands placed upon the musculoskeletal system by individual postures may allow experienced instructors and therapists to develop safe and effective yoga programs which reduce undesirable side effects. Thus, we used biomechanical methods to quantify the lower extremity joint angles, joint moments of force, and muscle activities of 21 Hatha yoga postures, commonly used in senior yoga programs. Twenty older adults, 70.7 years ± 3.8 years, participated in a 32-wk yoga class (2 d/wk) where they learned introductory and intermediate postures (asanas). They then performed the asanas in a motion analysis laboratory. Kinematic, kinetic, and electromyographic data was collected over three seconds while the participants held the poses statically. Profiles illustrating the postures and including the biomechanical data were then generated for each asana. Our findings demonstrated that Hatha yoga postures engendered a range of appreciable joint angles, JMOFs, and muscle activities about the ankle, knee, and hip, and that demands associated with some postures and posture modifications were not always intuitive. They also demonstrated that all of the postures elicited appreciable rectus abdominis activity, which was up to 70% of that induced during walking.

Lower-limb dynamics and clinical outcomes for habitually shod runners who transition to barefoot running

OBJECTIVES Recent investigations have revealed lower vertical loading rates and knee energy absorption amongst experienced barefoot runners relative to those who rear-foot strike (RFS). Although this has led to an adoption of barefoot running amongst many recreational shoe runners, recent investigations indicate that the experienced barefoot pattern is not immediately realized. Therefore, the purpose this investigation was to quantify changes in lower-extremity dynamics and clinical outcomes measures for habitually shod runners who perform a transition to barefoot running. DESIGN & PARTICIPANTS We examined lower-extremity dynamics and clinical outcomes for 26 RFS shod runners who performed an 8-10 week transition to barefoot running. SETTING Runners were evaluated at the University of Southern Californias Musculoskeletal Biomechanics Research Laboratory. MAIN OUTCOME MEASURES Foot-strike patterns, vertical load rates, and joint energetics were evaluated before and after the transition using inverse dynamics. Clinical assessments were conducted throughout the transition by two licensed clinicians. RESULTS Eighteen of the 26 runners successfully completed the transition: 7 maintained a RFS, 8 adopted a mid-foot strike (MFS), and 3 adopted a forefoot strike (FFS) during novice barefoot running. Following the transition, novice MFS/FFS runners often demonstrated reversions in strike-patterns and associated reductions in ankle energetics. We report no change in loading rates and knee energy absorption across transition time points. Importantly, there were no adverse events other than transient pain and soreness. CONCLUSIONS These findings indicate that runners do not innately adopt the biomechanical characteristics thought to lower injury risk in-response to an uninstructed barefoot running transition.

Spatiotemporal characteristics of habitually shod runners change when performing barefoot running

IntroductionHabitually shod rear-foot strike (RFS) runners demonstrate changes in spatiotemporal variables when running barefoot; however, it is unknown whether these changes are a function of running barefoot and/or adopting different foot-strike patterns. Therefore, the purpose of this study was to examine changes in spatiotemporal variables when habitually shod RFS runners transition to barefoot running.MethodsInverse dynamic methodology was used to examine 22 habitually shod RFS runners who performed overground running, shod and barefoot. Runners were grouped according to their novice barefoot foot-strike pattern: RFS, mid-foot strike (MFS) and forefoot strike (FFS). Runners were also grouped to examine differences between shod and barefoot running.ResultsOf the 22 RFS shod runners, 5 adopted a FFS, 9 adopted a MFS, and 8 maintained a RFS during novice barefoot running. We report a significant main effect of running barefoot for spatiotemporal variables, but not for foot-strike pattern. Relative to when shod, all groups of runners took shorter strides and steps. RFS and MFS runners also exhibited higher step frequency and exhibited shorter step and cycle times, while RFS and FFS runners both exhibited shorter stance times. These findings indicate that barefoot running has a significant influence on spatiotemporal measures, regardless of utilized foot-strike pattern.

Tibialis posterior muscle activation profiles in novice barefoot runners before and after exertion

Habitual barefoot (BF) runners present with a mid-foot (MFS) or forefoot strike (FFS) at foot contact (FC), whereas habitually shod (SH) runners typically present with a rearfoot strike (RFS) (Lieberman et al. 2010). A RFS is characterised by a centre of pressure (COP) profile that is initially posterolaterally oriented, and moves medially and anteriorly until toe-off (Cavanagh and Lafortune 1980). In contrast, in a MFS, there is an initial anterior movement, followed by a posterior and medial migration after FC, followed by anterolateral movement until toe-off (Cavanagh and Lafortune 1980). The more anterior strike pattern results in an increased reliance on the plantar flexors to eccentrically lower the body (Divert et al. 2005, Lieberman et al. 2010). In conjunction with the change in footfall pattern, Divert et al. (2005) reported higher EMG pre-activation of the GM, GL and SOL in novice barefooters, running BF, than when running SH. Studies to date, however, have not characterised, nor quantified, the activation profile of the tibialis posterior (TP) during novice BF running.

Adaptations in plantar-flexor performance and length-tension relationship following a transition from shod to barefoot running

An estimated 10–20% of the US population are regular shod (SH) runners. Half of these runners are injured annually and 25% are injured at any given time (Fields et al. 2010). Recent anecdotal reports substantiate a claim first proposed by Robbins and Hanna (1987) that habitual barefoot (BF) runners have reduced lower-extremity injury rates compared to their SH counterparts. A shift from SH to BF running lends itself to a notable change from heel striking in shoes to forefoot striking when barefoot (Divert et al. 2005, Lieberman et al. 2010) This change points to an increase in eccentric demand about the ankle (Divert et al. 2005, Lieberman et al. 2010) during the weight acceptance phase of stance, leading to repetitive eccentric loading of the plantar-flexors and foot arch structures during running. This likely induces adaptations to the plantarflexors, intrinsic foot muscles and, Achilles tendon. Muscles demonstrate hypertrophic adaptions to eccentric exercise by increasing the resting fascicle length and muscle cross-sectional area (Potier et al. 2009). Muscles with longer fibres can generate force over a greater range of excursion, and at a greater absolute velocity (Butterfield et al. 2010). While these adaptations have been demonstrated in animal models and isolated training studies, the effect of functional training strategies in humans has not been fully investigated. Although the perceived benefits of BF running are associated with a forefoot strike landing pattern, the associated muscle and tendon adaptations of the shank and foot during the transition have not yet been examined. A subset of data from an ongoing prospective study is presented to demonstrate changes in ankle plantar-flexor peak torque (PT) performance in three habitually SH recreational runners (those running 16–40 km per week) who progressively transitioned into BF running over an 8-week period.