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Journal: Clinical biomechanics (Bristol, Avon)


BACKGROUND: Dynamic postural stability is defined as the ability to transition from a dynamic movement to a stable condition over one’s base of support. Measures of dynamic stability have been used extensively to classify ankle instability status and assist clinicians with ankle injury interventions. Therefore, the purpose of this study was to determine if current methods of quantifying dynamic stability are accurate in differentiating among healthy, coper, and unstable ankles. METHODS: One hundred ninety four Division-I collegiate athletes (football, volleyball, field hockey, men’s/women’s soccer, men’s/women’s lacrosse, men’s/women’s basketball) volunteered for this study. Participants were categorized into healthy, coper, and stable groups by a self-reported questionnaire and previous history of ankle injuries. Dynamic postural stability was assessed using the Multi-Directional Dynamic Stability Protocol by jumping and landing single-legged onto a force platform from four different directions. Receiver operator curves were used to analyze the accuracy of current techniques of calculating dynamic stability among groups. FINDINGS: None of the existing methods were found to be accurate in differentiating ankle instability status in any of the jump landings. INTERPRETATION: Researchers have commonly used these existing methods to quantify dynamic postural stability. None of the current calculation techniques worked with our jump landing protocol. Researchers need to pay attention to the protocol and calculation technique pairings in that using inaccurate measures of dynamic postural stability makes any findings of that research ineffective. Therefore, this challenges researchers to develop a more accurate calculation to quantify dynamic postural stability, or develop a jump landing protocol that exposes sensorimotor deficits in the more able-bodied population.

Concepts: Foot, Accuracy and precision, Centrifugation, Stability, Ankle, Instability, Sprained ankle, Landing


BACKGROUND: The internal joint contact forces experienced at the lower limb have been frequently studied in activities of daily living and rehabilitation activities. In contrast, the forces experienced during more dynamic activities are not well understood, and those studies that do exist suggest very high degrees of joint loading. METHODS: In this study a biomechanical model of the right lower limb was used to calculate the internal joint forces experienced by the lower limb during vertical jumping, landing and push jerking (an explosive exercise derived from the sport of Olympic weightlifting), with a particular emphasis on the forces experienced by the knee. FINDINGS: The knee experienced mean peak loadings of 2.4-4.6×body weight at the patellofemoral joint, 6.9-9.0×body weight at the tibiofemoral joint, 0.3-1.4×body weight anterior tibial shear and 1.0-3.1×body weight posterior tibial shear. The hip experienced a mean peak loading of 5.5-8.4×body weight and the ankle 8.9-10.0×body weight. INTERPRETATION: The magnitudes of the total (resultant) joint contact forces at the patellofemoral joint, tibiofemoral joint and hip are greater than those reported in activities of daily living and less dynamic rehabilitation exercises. The information in this study is of importance for medical professionals, coaches and biomedical researchers in improving the understanding of acute and chronic injuries, understanding the performance of prosthetic implants and materials, evaluating the appropriateness of jumping and weightlifting for patient populations and informing the training programmes of healthy populations.

Concepts: Knee, Joint, Sartorius muscle, Knowledge, Synovial joint, Joints, Human leg, Popliteal artery


Dual task paradigm states that the introduction of a second task during a cognitive or motor performance results in a decreased performance in either task. Treadmill walk, often used in clinical applications of dual task testing, has never been compared to overground walk, to ascertain its susceptibility to interference from a second task. We compared the effects of overground and treadmill gait on dual task performance.

Concepts: Activity, Task, Introduction, Walking, Software testing, Debut albums, Steve Morse


BACKGROUND: The extrinsic toe flexors, flexor hallucis longus and flexor digitorum longus, play an important role in stabilizing the longitudinal arch and supporting high forefoot loads during the stance phase of gait. It was hypothesized that these muscles function isometrically during stance, a strategy thought to provide efficient energy transfer across adjoining body segments, but one for which there is little direct experimental evidence in vivo or in situ. METHODS: Eight lower extremity cadavers were loaded into a robotic apparatus that simulates the kinematics and extrinsic muscle activity of the foot and distal tibia during the stance phase of gait. Instantaneous tendon excursions and forces of the extrinsic toe flexors, as well as plantar pressure distributions during stance, were measured under two muscle control strategies: (1) force feedback control, where tendon forces were matched to forces predicted from normal electromyographic patterns and (2) isometric displacement control, where the representative myotendinous junction was held in a constant location. RESULTS: Tendon excursions of the flexor hallucis longus (7.18 (1.75)mm) and flexor digitorum longus (6.32 (1.74)mm) under force feedback control were small relative to optimal muscle fiber length (13.6% and 14.2%, respectively). Instantaneous tendon forces and plantar pressure variables were not different (P=0.112-0.912) between the two different muscle control strategies for either muscle. INTERPRETATION: These findings suggest that the extrinsic toe flexors function isometrically during the stance phase of gait in vivo.

Concepts: Energy, Muscle, In vivo, Electromyography, Control theory, Classical mechanics, In situ, Flexor hallucis longus muscle


This study aimed to investigate the influence of the screw location and plate working length of a locking plate construct at the distal femur on interfragmentary movement under physiological loading.

Concepts: Plate tectonics, Femur


Minimalist shoes have gained popularity recently because it is speculated to strengthen the foot muscles and foot arches, which may help to resist injuries. However, previous studies provided limited evidence supporting the link between changes in muscle size and footwear transition. Therefore, this study sought to examine the effects of minimalist shoes on the intrinsic and extrinsic foot muscle volume in habitual shod runners. The relationship between participants' compliance with the minimalist shoes and changes in muscle õvolume was also evaluated.

Concepts: Foot, Muscle, Muscular system, The Link REIT, Shoe, Intrinsic and extrinsic properties, Philosophical terminology, Arches of the foot


Running popularity has increased resulting in a concomitant increase in running-related injuries with patellofemoral pain most commonly reported. The purpose of this study was to determine whether gait retraining by modifying footstrike patterns from rearfoot strike to forefoot strike reduces patellofemoral pain and improves associated biomechanical measures, and whether the modification influences risk of ankle injuries.

Concepts: Randomized controlled trial


To determine the influence of femur and tibia rotations in the transverse and frontal planes on patella cartilage stress.


The metatarsal bones of the foot are particularly susceptible to stress fracture owing to the high strains they experience during the stance phase of running. Shoe cushioning and stride length reduction represent two potential interventions to decrease metatarsal strain and thus stress fracture risk.

Concepts: Foot, Orthopedic surgery, Solid mechanics, Length, Shoe, Footwear, Tarsus, Metatarsus


Motor control exercise was claimed to improve spinal stability in patients with chronic non-specific back pain, but to investigate the effectiveness of this exercise, other outcome measures have been used rather than spinal stability itself. The aim of our study is to assess motor control exercise effects on spinal stability using a biomechanical model.

Concepts: Low back pain, Back pain