Altered control strategy between leading and trailing leg increases knee adduction moment in the elderly while descending stairs

The aim of the study was to examine the external knee adduction moments in a group of older and younger adults while descending stairs and thus the possibility of an increased risk of knee osteoarthritis due to altered knee joint loading in the elderly. Twenty-seven older and 16 younger adults descended a purpose-built staircase. A motion capture system and a force plate were used to determine the subjects' 3D kinematics and ground reaction forces (GRF) during locomotion. Calculation of the leg kinematics and kinetics was done by means of a rigid, three-segment, 3D leg model. In the initial portion of the support phase, older adults showed a more medio-posterior GRF vector relative to the ankle joint, leading to lower ankle joint moments (P<0.05). At the knee, the older adults demonstrated a more medio-posterior directed GRF vector, increasing in knee flexion and adduction in the second part of the single support phase (P<0.05). Further, GRF magnitude was lower in the initial and higher in the mid-portions of the support phase for the elderly (P<0.05). The results show that older adults descend stairs by using the trailing leg before the initiation of the double support phase more compared to the younger ones. The consequence of this altered control strategy while stepping down is a more medially directed GRF vector increasing the magnitude of external knee adduction moment in the elderly. The observed changes between leading and trailing leg in the elderly may cause a redistribution of the mechanical load at the tibiofemoral joint, affecting the initiation and progression of knee osteoarthritis in the elderly.     

Combined effects of speed and directional change on postural adjustments during gait initiation

The study of gait initiation (GI) has primarily focused on gait initiated in a forward direction, however, in everyday life, GI is often combined with a directional change. Ten young adults initiated gait with their right foot in four directions (to the left: −15°, straight ahead: 0°, to the right: 15° and 30°) at self-selected and fast gait speeds. The relationship between starting direction of GI and the lateral center of foot pressure displacement for normal (r² = 0.57) and fast gait speed (r² = 0.75) indicated that the lateral component plays an important role with regards to controlling the desired direction of gait. At the first step of the swing limb, the progression velocity of the center of mass (CM) remained slower for the 30° condition only, whereas no difference was found between directions for CM velocity perpendicular to the intended direction. These results suggest that postural adjustments are scaled to initiate gait in a predetermined direction. By the first step, the orientation of CM is toward the intended direction of gait, however, when gait is initiated in combination with a large change in direction, additional adjustments may be required to reach the intended progression velocity.     

Footwear affects the gearing at the ankle and knee joints during running

The objective of the study was to investigate the adjustment of running mechanics by wearing five different types of running shoes on tartan compared to barefoot running on grass focusing on the gearing at the ankle and knee joints. The gear ratio, defined as the ratio of the moment arm of the ground reaction force (GRF) to the moment arm of the counteracting muscle tendon unit, is considered to be an indicator of joint loading and mechanical efficiency. Lower extremity kinematics and kinetics of 14 healthy volunteers were quantified three dimensionally and compared between running in shoes on tartan and barefoot on grass. Results showed no differences for the gear ratios and resultant joint moments for the ankle and knee joints across the five different shoes, but showed that wearing running shoes affects the gearing at the ankle and knee joints due to changes in the moment arm of the GRF. During barefoot running the ankle joint showed a higher gear ratio in early stance and a lower ratio in the late stance, while the gear ratio at the knee joint was lower during midstance compared to shod running. Because the moment arms of the counteracting muscle tendon units did not change, the determinants of the gear ratios were the moment arms of the GRF's. The results imply higher mechanical stress in shod running for the knee joint structures during midstance but also indicate an improved mechanical advantage in force generation for the ankle extensors during the push-off phase.     

Orthotic effect of a stabilising mechanism in the surface of gymnastic mats on foot motion during landings.

The purpose of this study was to examine two hypotheses: (a) mat hardness affects foot motion during landing; (b) the influence of a surface stabilising interface integrated in a mat on foot motion is detectable. Two studies were carried out: In the first one, six female gymnasts performed barefoot landings from different falling heights onto three mats having different hardness. In the second study, a stabilising mechanism was integrated in the surface of three new mats with different hardness. Three high speed video cameras (250Hz) captured the motion of the left leg and foot. These were modelled by means of a four rigid body system. The maximal eversion at the ankle joint was not influenced by the different mats (hard: 4.6 degrees +/-1.9 to 9.3 degrees +/-3.4, medium: 3.1 degrees +/-2.7 to 7.4 degrees +/-3.5, soft: 4.8 degrees +/-2.1 to 8.4 degrees +/-3.5). The soft mat without the stabilised surface showed higher eversion values (p<0.05) between forefoot and rearfoot (medial joint: hard: 5.1 degrees +/-3.2 to 7.3 degrees +/-3.3, medium: 6.9 degrees +/-3.1 to 7.5 degrees +/-2.9, soft: 12.7 degrees +/-4.1 to 13.4 degrees +/-3.3; lateral joint: hard: 8.5 degrees +/-3.1 to 9.7 degrees +/-1.1, medium: 9.5 degrees +/-2.6 to 11.2 degrees +/-3.3, soft: 12.1 degrees +/-2.3 to 15.7 degrees +/-3.3). For the mats with the surface stabilising interface, the different hardness did not cause any significant differences in maximal eversion values at the medial (hard: 1.5 degrees +/-3.3 to 5.5 degrees +/-4.5, medium: 1.3 degrees +/-3.5 to 5.1 degrees +/-3.6, soft: 0.7 degrees +/-4.9 to 5.4 degrees +/-4.2) nor at the lateral (hard: 11.3 degrees +/-4.2 to 17.3 degrees +/-4.2, medium: 12.3 degrees +/-4.8 to 17.1 degrees +/-3.7, soft: 11.5 degrees +/-4.6 to 17.1 degrees +/-4.3) forefoot joints. The structure of the mat and the consequent deformation hollow did not influence the kinematics of the ankle joint during landings, but it influenced the motion at the medial and the lateral forefoot joints. By means of a stabilised surface, it is possible to reduce the influence of mat deformation on the maximal eversion between forefoot and rearfoot.     

Effect of contraction form and contraction velocity on the differences between resultant and measured ankle joint moments

During a maximal isometric plantar flexion effort the moment measured at the dynamometer differs from the resultant ankle joint moment. The present study investigated the effects of contraction form and contraction velocity during isokinetic plantar/dorsal flexion efforts on the differences between resultant and measured moments due to the misalignment between ankle and dynamometer axes. Eleven male subjects (age: 31+/-6 years, mass: 80.6+/-9.6 kg, height: 178.4+/-7.4 cm) participated in this study. All subjects performed isometric-shortening-stretch-isometric contractions induced by electrical stimulation at three different angular velocities (25 degrees /s, 50 degrees /s and 100 degrees /s) on a customised dynamometer. The kinematics of the leg were recorded using the vicon 624 system with eight cameras operating at 250 Hz. The resultant moments at the ankle joint were calculated through inverse dynamics. The relative differences between resultant and measured ankle joint moments due to axis misalignment were fairly similar in all phases of the isometric-shortening-stretch-isometric contraction (in average 5-9% of the measured moment). Furthermore these findings were independent of the contraction velocity. During dynamic plantar/dorsal flexion contractions the differences between measured and resultant joint moment are high enough to influence conclusions regarding the mechanical response of ankle extensor muscles. However the relative differences were not increased during dynamic contractions as compared to isometric contractions.     

Abdominal muscle activation changes if the purpose is to control pelvis motion or thorax motion

The aim of this study was to compare trunk muscular recruitment and lumbar spine kinematics when motion was constrained to either the thorax or the pelvis. Nine healthy women performed four upright standing planar movements (rotations, anterior–posterior translations, medial–lateral translations, and horizontal circles) while constraining pelvis motion and moving the thorax or moving the pelvis while minimizing thorax motion, and four isometric trunk exercises (conventional curl-up, reverse curl-up, cross curl-up, and reverse cross curl-up). Surface EMG (upper and lower rectus abdominis, lateral and medial aspects of external oblique, internal oblique, and latissimus dorsi) and 3D lumbar displacements were recorded. Pelvis movements produced higher EMG amplitudes of the oblique abdominals than thorax motions in most trials, and larger lumbar displacements in the medial–lateral translations and horizontal circles. Conversely, thorax movements produced larger rotational lumbar displacement than pelvis motions during rotations and higher EMG amplitudes for latissimus dorsi during rotations and anterior–posterior translations and for lower rectus abdominis during the crossed curl-ups. Thus, different neuromuscular compartments appear when the objective changes from pelvis to thorax motion. This would suggest that both movement patterns should be considered when planning spine stabilization programs, to optimize exercises for the movement and muscle activations desired.     

Adaptations in the gait pattern with experimental hamstring pain

Pain changes movement but most studies have focused on basic physiological adaptations during non-functional movement tasks. The existing studies on how pain affects lower extremity gross movement biomechanics have primarily involved movements in which the quadriceps is the primary muscle and little attention has been given to how pain in other muscles affects functional movement. The purpose of this study was to investigate the changes in the gait patterns of healthy subjects that occur during experimental muscle pain in the biceps femoris.In a cross-over study design, 14 healthy volunteers underwent EMG assisted 3D gait analyses before, during and after experimental biceps femoris pain induced by intramuscular injections of hypertonic saline. Isotonic saline injections were administered as a non-painful control.The experimental biceps femoris pain led to reductions in hip extensor moments, knee flexor and lateral rotator moments. No changes in lower extremity kinematics and EMG activity in any of the recorded muscles were observed.It is concluded that experimental muscle pain in the biceps femoris leads to changes in the gait pattern in agreement with unloading of the painful muscle. The changes are specific to the painful muscle. The present study provides support to the theory that musculoskeletal pain is a protective signal leading to changes in movement patterns that serve to unload the painful tissue.     

Associations between the masticatory system and muscle activity of other body districts. A meta-analysis of surface electromyography studies

The aim of this meta-analysis regarding the use of surface electromyography (sEMG) is to assess the scientific evidence for detectable correlations between the masticatory system and muscle activity of the other body districts, particularly those mainly responsible for body posture. A literature survey was performed using the PubMed database, covering the period from January 1966 to April 2011, and choosing medical subject headings. After selection, five articles qualified for the final analysis. One study article was judged to be of medium quality, the remaining four of low quality. No study included a control group or follow-up; in only one study, subjects with impairment of the masticatory system were enrolled. In all studies, detectable correlations between the masticatory systems and muscle activity of the other body districts, or vice versa, were found; however, after a reappraisal of the data provided in these studies, only weak correlations were found, which reached biological, but not clinical relevance. With the limitations that arise from the poor methodological quality of the published study reports discussed here, the conclusion is that a correlation between the masticatory system and muscle activity of the other body districts might be detected through sEMG under experimental conditions; however, this correlation has little clinical relevance. While more investigations with improved levels of scientific evidence are needed, the current evidence does not support clinically relevant correlations between the masticatory system and the muscle activity of other body districts, including those responsible for body posture.     

Effect of the pole--human body interaction on pole vaulting performance

The purposes of this study were: (a) to examine the interactions between the athlete and the pole and the possibility for the athlete to take advantage of the pole's elasticity by means of muscular work and (b) to develop performance criteria during the interaction between the athlete and the pole in pole vaulting. Six athletes performed 4-11 trials each, at 90% of their respective personal best performance. All trials were recorded using four synchronized, genlocked video cameras operating at 50 Hz. The ground reaction forces exerted on the bottom of the pole were measured using a planting box fixed on a force plate (1000 Hz). The interaction between athlete and pole may be split into two parts. During the first part, energy is transferred into the pole and the total energy of the athlete decreases. The difference between the energy decrease of the athlete and the pole energy is an indicator of the energy produced by the athletes by means of muscular work (criterion 1). During the second part of the interaction, energy is transferred back to the athlete and the total energy of the athlete increases. The difference between the returned pole energy and the amount of energy increase of the athlete defines criterion 2. In general, the function of the pole during the interaction is: (a) store part of the kinetic energy that the athlete achieved during the run up as strain energy and convert this strain energy into potential energy of the athlete, (b) allow the active system (athlete) to produce muscular work to increase the total energy potential.     

Effect of different ankle- and knee-joint positions on gastrocnemius medialis fascicle length and EMG activity during isometric plantar flexion

The purpose of this study was to provide evidence on the fact that the observed decrease in EMG activity of the gastrocnemius medialis (GM) at pronounced knee flexed positions is not only due to GM insufficiency, by examining muscle fascicle lengths during maximal voluntary contractions at different positions. Twenty-two male long distance runners (body mass: 78.5+/-6.7 kg, height: 183+/-6 cm) participated in the study. The subjects performed isometric maximal voluntary plantar flexion contractions (MVC) of their left leg at six ankle-knee angle combinations. To examine the resultant ankle joint moments the kinematics of the left leg were recorded using a Vicon 624 system with 8 cameras operating at 120 Hz. The EMG activity of GM, gastrocnemius lateralis (GL), soleus (SOL) and tibialis anterior (TA) were measured using surface electromyography. Synchronously, fascicle length and pennation angle values of the GM were obtained at rest and at the plateau of the maximal plantar flexion using ultrasonography. The main findings were: (a) identifiable differences in fascicle length of the GM at rest do not necessarily imply that these differences would also exist during a maximal isometric plantar flexion contraction and (b) the EMG activity of the biarticular GM during the MVC decreased at a pronounced flexed knee-joint position (up to 110 degrees ) despite of no differences in GM fascicle length. It is suggested that the decrease in EMG activity of the GM at pronounced knee flexed positions is due to a critical force-length potential of all three muscles of the triceps surae.