How do load carriage and walking speed influence trunk coordination and stride parameters?

To determine the effects of load carriage and walking speed on stride parameters and the coordination of trunk movements, 12 subjects walked on a treadmill at a range of walking speeds (0.6-1.6 m s(-1)) with and without a backpack containing 40% of their body mass. It was hypothesized that compared to unloaded walking, load carriage decreases transverse pelvic and thoracic rotation, the mean relative phase between pelvic and thoracic rotations, and increases hip excursion. In addition, it was hypothesized that these changes would coincide with a decreased stride length and increased stride frequency. The findings supported the hypotheses. Dimensionless analyses indicated that there was a significantly larger contribution of hip excursion and smaller contribution of transverse plane pelvic rotation to increases in stride length during load carriage. In addition, there was a significant effect of load carriage on the amplitudes of transverse pelvic and thoracic rotation and the relative phase of pelvic and thoracic rotation. It was concluded that the shorter stride length and higher stride frequency observed when carrying a backpack is the result of decreased pelvic rotation. During unloaded walking, increases in pelvic rotation contribute to increases in stride length with increasing walking speed. The decreased pelvic rotation during load carriage requires an increased hip excursion to compensate. However, the increase in hip excursion is insufficient to fully compensate for the observed decrease in pelvis rotation, requiring an increase in stride frequency during load carriage to maintain a constant walking speed.     

Timing and magnitude of lumbar spine contribution to trunk forward bending and backward return in patients with acute low back pain

Alterations in the lumbo-pelvic coordination denote changes in neuromuscular control of trunk motion as well as load sharing between passive and active tissues in the lower back. Differences in timing and magnitude aspects of lumbo-pelvic coordination between patients with chronic low back pain (LBP) and asymptomatic individuals have been reported; yet, the literature on lumbo-pelvic coordination in patients with acute LBP is scant. A case-control study was conducted to explore the differences in timing and magnitude aspects of lumbo-pelvic coordination between females with (n=19) and without (n=19) acute LBP. Participants in each group completed one experimental session wherein they performed trunk forward bending and backward return at preferred and fast paces. The amount of lumbar contribution to trunk motion (as the magnitude aspect) as well as the mean absolute relative phase (MARP) and deviation phase (DP) between thoracic and pelvic rotations (as the timing aspect) of lumbo-pelvic coordination were calculated. The lumbar contribution to trunk motion in the 2nd and the 3rd quarters of both forward bending and backward return phases was significantly smaller in the patient than the control group. The MARP and the DP were smaller in the patient vs. the control group during entire motion. The reduced lumbar contribution to trunk motion as well as the more in-phase and less variable lumbo-pelvic coordination in patients with acute LBP compared to the asymptomatic controls is likely the result of a neuromuscular adaptation to reduce painful deformation and to protect injured lower back tissues.     

Dynamic analysis of load carriage biomechanics during level walking

This paper describes an investigation into the biomechanical effects of load carriage dynamics on human locomotion performance. A whole body, inverse dynamics gait model has been developed which uses only kinematic input data to define the gait cycle. To provide input data, three-dimensional gait measurements have been conducted to capture whole body motion while carrying a backpack. A nonlinear suspension model is employed to describe the backpack dynamics. The model parameters for a particular backpack system can be identified using a dynamic load carriage test-rig. Biomechanical assessments have been conducted based on combined gait and pack simulations. It was found that the backpack suspension stiffness and damping have little effect on human locomotion energetics. However, decreasing suspension stiffness offers important biomechanical advantages. The peak values of vertical pack force, acting on the trunk, and lower limb joint loads are all moderated. This would reduce shoulder strap pressures and the risk of injury when heavy loads are carried.     

Effects of a hip belt on transverse plane trunk coordination and stability during load carriage

This study examined the transverse plane kinematics of the pelvis, thorax and head while participants walked at a range of speeds on a treadmill under three load conditions: no load, with a loaded backpack with no hip belt and with a loaded backpack with a hip belt. Research has suggested that one mechanism for adapting to heavy loads carried with no hip belt is to reduce the amplitudes and relative phase of transverse plane pelvic and thoracic rotations, in order to minimize rotational torque on the loaded upper body. Transverse plane rotation amplitudes of the pelvis, thorax, backpack and head were calculated from 3D kinematic data for 12 healthy subjects, walking at speeds of 0.5, 0.9, 1.3 and 1.7 ms(-1). Relative phase relation and its variability were also computed for pelvis-thorax rotations and backpack-thorax rotations. Stability of the coordination pattern was estimated as an inverse function of the variability in relative phase. The backpack with the hip belt allowed significantly larger transverse plane rotation amplitudes, along with increased stability of the coordination pattern, than the backpack with no hip belt. Motion patterns of the backpack and thorax suggested that the backpack frame was used to assist with the deceleration and reversal of the loaded thorax, driven by the pelvis through the hip belt connection. Use of the frame in this way may have required less trunk muscle activation and allowed for improved pattern stability.     

Preliminary simulation model toward the study of the effects caused by different mandibular advancement devices in OSAS treatment

Abstract

The paper aims to evaluate the effects caused by a Mandibular Advancement Device (MAD) for Obstructive Sleep Apnoea Syndrome (OSAS) treatment. This study is based on Finite Element Method (FEM) for evaluating the load distribution on temporomandibular joint, especially on the mandibular condyle and disc, and on periodontal ligaments. The stress values on condyle and periodontal ligaments lead authors to consider MAD a safe procedure even for a long period. The obtained results also show the relationship between MAD material and load distribution at the periodontal ligaments. The paper is a step toward future analyses for studying and comparing the effects of MAD features, such as material, shape and dimensions, in order to allow the clinician prescribing the most fitting device.     

Thorax and pelvis kinematics during the downswing of male and female skilled golfers

Thorax and pelvis motion during the golf swing have most frequently been described for male golfers at discrete points during the swing, such as top of backswing (TBS) and ball contact (BC). Less is known about the continual motion and coordination of the thorax and pelvis throughout the downswing for either male or female golfers. The purpose of this study was to present detailed 3D kinematic profiles of thorax and pelvis motion during the downswing, and to determine if differences in kinematics exist between male and female skilled golfers. Thorax and pelvis data were collected from 19 male (26±7 years) and 19 female (25±7 years) skilled golfers (handicap ≤4) using an optical motion analysis system. 3D segment position, orientation and angular velocity were calculated, along with phase plane trajectories and thorax–pelvis separation angles. At BC males had greater pelvis posterior tilt, greater pelvis and thorax lateral tilt to the right, and less pelvis and thorax axial rotation to the left compared to females. Males achieved greater peak thorax and pelvis angular velocity, and angular velocity at BC, in the anterior–posterior and lateral tilt directions. Phase plane trajectories revealed that males and females had similar thorax lateral tilt and anterior–posterior tilt angular velocity–displacement relationships at TBS, yet by BC males had greater tilt angles and velocities compared to females. Collectively, the results suggest that male and female skilled golfers have different kinematics for thorax and pelvis motion, predominantly for lateral and anterior–posterior tilt. What might be considered optimal swing characteristics for male golfers should not be generalized to female golfers.     

Pelvic function in anuran jumping: Interspecific differences in the kinematics and motor control of the iliosacral articulation during take‐off and landing

Although the anuran pelvis is thought to be adapted for jumping, the function of the iliosacral joint has seen little direct study. Previous work has contrasted the basal “ lateral‐bender ” pelvis from the “ rod‐like ” pelvis of crown taxa hypothesized to function as a sagittal hinge to align the trunk with take‐off forces. We compared iliosacral movements and pelvic motor patterns during jumping in the two pelvic types. Pelvic muscle activity patterns, iliosacral anteroposterior (AP) movements and sagittal bending of the pelvis during the take‐off and landing phases were quantified in lateral bender taxa Ascaphus (Leiopelmatidae) and Rhinella (Bufonidae) and the rod‐like Lithobates (Ranidae). All three species exhibit sagittal extension during take‐off, therefore, both pelvic types employ a sagittal hinge. However, trunk elevation occurs significantly earlier in the anuran rod‐like pelvis. Motor patterns confirm that the piriformis muscles depress the urostyle while the longissimus dorsi muscles elevate the trunk during take‐off. However, the coccygeoiliacus muscles also produce anterior translation of the sacrum on the ilia. A new model illustrates how AP translation facilitates trunk extension in the lateral‐bender anurans that have long been thought to have limited sagittal bending. During landing, AP translation patterns are similar because impact forces slide the sacrum from its posterior to anterior limits. Sagittal flexion during landing differs among the three taxa depending on the way the species land. AP translation during landing may dampen impact forces especially in Rhinella in which pelvic function is tuned to forelimb‐landing dynamics. The flexibility of the lateral‐bender pelvis to function in sagittal bending and AP translation helps to explain the retention of this basal configuration in many anurans. The novel function of the rod‐like pelvis may be to increase the rate of trunk elevation relative to faster rates of energy release from the hindlimbs enabling them to jump farther. J. Morphol. 277:1539–1558, 2016. © 2016 Wiley Periodicals, Inc.     

Effects of load carriage and fatigue on gait characteristics

The objective of this study was to determine the main and interactive effects of load carriage and fatigue on gait characteristics. Twelve young male participants were recruited in this study. Fatiguing protocol involved a running exercise, and fatigue was considered to be induced when the participants first gave an RPE rating at or above 17. Gait data were collected when the participants walked on a medical treadmill at their self-selected comfortable speed, both before and right after the fatiguing exercise. Different back-carrying loads (i.e. 0, 7.5, and 15 kg) were applied separately to the participants during the walking trials. Gait variability measures and kinematic measures were used to quantify gait characteristics. The results showed that gait width variability, hip range of motion, and trunk range of motion increased with fatigue and with the application of the heavy load. These findings suggest that both fatigue and load carriage compromise gait. Findings from this study can help better understand how fatigue and load carriage affect gait, and further aid in developing interventions that are able to minimize fall risks especially with the application of fatigue and/or external load.     

Effects of fatigue on lower limb,pelvis and trunk kinematics and muscle activation: Gender differences

Background: Muscle fatigue is associated with biomechanical changes that may lead to anterior cruciate ligament (ACL) injuries. Alterations in trunk and pelvis kinematics may also be involved in ACL injury. Although some studies have compared the effects of muscle fatigue on lower limb kinematics between men and women, little is known about its effects on pelvis and trunk kinematics. The aim of the study was to compare the effects of fatigue on lower limb, pelvis and trunk kinematics and muscle activation between men and women during landing. Methods: The participants included forty healthy subjects. We performed kinematic analysis of the trunk, pelvis, hip and knee and muscle activation analysis of the gluteal muscles, vastus lateralis and biceps femoris, during a single-leg landing before and after fatigue. Results: Men had greater trunk flexion than women after fatigue. After fatigue, a decrease in peak knee flexion and an increase in Gmax and BF activation were observed. Conclusion: The increase in the trunk flexion can decrease the anterior tibiofemoral shear force resulted from the lower knee flexion angle, thereby decreasing the stress on the ACL.     

Ankle and knee moment and power adaptations are elicited through load carriage conditioning in males

Soldiers routinely conduct load carriage and physical training to meet occupational requirements. These tasks are physically arduous and are believed to be the primary cause of musculoskeletal injury. Physical training can help mitigate injury risk when specifically designed to address injury mechanisms and meet task demands. This study aimed to assess lower-limb biomechanics and neuromuscular adaptations during load carriage walking in response to a 10-week evidence-based physical training program. Thirteen male civilian participants donned 23 kg and completed 5 km of load carriage treadmill walking, at 5.5 km h⁻¹ before and after a 10-week physical training program. Three-dimensional motion capture and force plate data were acquired in over-ground walking trials before and after treadmill walking. These data were inputs to a musculoskeletal model which estimated lower-limb joint kinematics and kinetics (i.e., moments and powers) using inverse kinematics and dynamics, respectively. A two-way analysis of variance revealed significant main effect of training for kinematic and kinetics parameters at the knee and ankle joints (p < 0.05). Post-Hoc comparisons demonstrated a significant decrease (4.2%) in total negative knee power between pre- and post-March 5 km measures after training (p < 0.05). Positive power contribution shifted distally after training, increasing at the post-march measure from 39.9% to 43.6% at the ankle joint (p < 0.05). These findings demonstrate that a periodised training program may reduce injury risk through favourable ankle and knee joint adaptations.     

Backpack load affects lower limb muscle activity patterns of female hikers during prolonged load carriage

This study investigated the effect of prolonged load carriage on lower limb muscle activity displayed by female recreational hikers. Electromyography (EMG) signals from vastus lateralis (VL), biceps femoris (BF), semitendinosus (ST), tibialis anterior (TA) and gastrocnemius (GM) were recorded for fifteen female hikers carrying four loads (0%, 20%, 30% and 40% body weight (BW)) over 8 km. Muscle burst duration, muscle burst onset relative to initial contact and integrated EMG signals (iEMG) were calculated to evaluate muscle activity, whereas the shift in mean power frequency (MPF) was used to evaluate muscle fatigue. Increased walking distance significantly decreased the MPF of TA; decreased the iEMG for VL, ST and GM; and shortened VL muscle burst duration. Furthermore, carrying 20–40% BW loads significantly increased VL and GM iEMG and increased BF muscle burst duration, whereas a 40% BW load caused a later VL muscle burst onset. The differences observed in muscle activity with increased load mass seem to be adjustments aimed at maintaining balance and attenuating the increased loads placed on the lower limbs during gait. Based on the changes in muscle activity, a backpack load limit of 30% BW may reduce the risk of lower limb injury for female hikers during prolonged walking.     

Effect of unilateral load carriage on postures and gait symmetry in ground reaction force during walking

Unilateral load carriage is more hazardous to the musculoskeletal system than bilateral load. The purpose of this study was to examine the effect of such asymmetric carriage on postures and gait symmetry in ground reaction force (GRF) during walking. Kinematics and GRF of 19 adults were recorded while they walked under five load conditions: no load, dumbbell (10 and 20% body weight) held in right and left hand, respectively. After loading, the trunk bent towards the loaded or unloaded side in right- and left-hand trials and under different load weight conditions. The amplitude of trunk bend increased with load, accompanied by decreased stride width, progressively inclined legs towards unloaded side and higher level of asymmetry in medial/lateral GRF (GRFm/l) and free vertical moment GRF (GRFm). The findings indicate the postural adjustment is likely related to the characteristics of load and the task experience and handedness of subject and the unilateral load increases the gait asymmetry in GRFm/l and GRFm.     

Role of trunk muscles in generating follower load in the lumbar spine of neutral standing posture

Recently, experimental results have demonstrated that the load carrying capacity of the human spine substantially increases under the follower load condition. Thus, it is essential to prove that a follower load can be generated in vivo by activating the appropriate muscles in order to demonstrate the possibility that the stability of the spinal column could be maintained through a follower load mechanism. The aim of this study was to analyze the coordination of the trunk muscles in order to understand the role of the muscles in generating the follower load. A three-dimensional finite element model of the lumbar spine was developed from T12 to S1 and 117 pairs of trunk muscles (58 pairs of superficial muscles and 59 pairs of deep muscles) were considered. The follower load concept was mathematically represented as an optimization problem. The muscle forces required to generate the follower load were predicted by solving the optimization problem. The corresponding displacements and rotations at all nodes were estimated along with the follower forces, shear forces, and joint moments acting on those nodes. In addition, the muscle forces and the corresponding responses were investigated when the activations of the deep muscles or the superficial muscles were restricted to 75% of the maximum activation, respectively. Significantly larger numbers of deep muscles were involved in the generation of the follower load than the number of superficial muscles, regardless of the restriction on muscle activation. The shear force and the resultant joint moment are more influenced by the change in muscle activation in the superficial muscles. A larger number of deep trunk muscles were activated in order to maintain the spinal posture in the lumbar spine. In addition, the deep muscles have a larger capability to reduce the shear force and the resultant joint moment with respect to the perturbation of the external load or muscle fatigue compared to the superficial muscles.     

Elevation of plasma gastrin and pancreatic polypeptide by electrical vagal stimulation in sheep: effects of sequential stimulation

Gastrin and pancreatic polypeptide (PP) are released into the circulation by vagal stimulation. The individual effects of the anterior and posterior vagal trunks on the release of these peptides are unknown. Four sheep were anaesthetized and studied acutely: both vagi were dissected at the hiatus and the trunks divided. In two sheep, the distal ends of the anterior trunks were stimulated for 5 min with an 8 V, 1 ms impulse at 10 Hz. After 1 h the posterior trunks were stimulated similarly. In the other two sheep, the posterior trunk was stimulated and after 1 h the anterior vagal trunk was stimulated. The anterior and posterior trunk equally stimulated the release of both gastrin and PP in four animals. The second stimulation in these four animals resulted in an 18-fold greater integrated response of gastrin and 20-fold greater response of PP. This potentiation to the second stimulus was observed in further experiments even when the same trunk, posterior or anterior, was stimulated twice. The similarity of influence of the anterior and posterior trunks for the release of PP suggests the existence of mechanisms for vagally stimulated PP release other than branches direct from the vagal trunks.     

Estimation of breast burn size

It is the authors' opinion that the size of chest burns on large-breasted women can be significantly underestimated, especially if the methods of calculation rely on burn charts, such as the Lund and Browder burns chart. This latter chart is based on data derived from only three women and eight men. The surface area of the torsos of 60 volunteers (20 men, 20 small-breasted women, and 20 large-breasted women) was measured using two well-established techniques. The torso surface area was divided into two parts: the anterior trunk and the posterior trunk (i.e., torso surface area = posterior trunk + anterior trunk). The anterior trunk was subdivided and the area above the costal margins defined as the pectoral region. These areas were measured separately for each individual. The volunteers' total body surface area was calculated using normograms, based on their weight and height. The area of each torso section was recorded as a percentage of the total body surface area and torso surface area. Whereas the torso surface area/total body surface area ratio did not vary significantly between the groups, the proportion of anterior to posterior trunk size did depend on the sex and on breast size. There was a direct correlation between the woman's bra cup size and the ratio of anterior-to-posterior trunk surface area. A simple chart was therefore derived that estimates the relative size of a woman's torso surface area once her bra cup size is known. Such a chart can be used to improve accuracy in adult female chest burn estimation, when used in conjunction with a burns chart. Breast burns in larger breasted women are underestimated when calculated using current burn charts. We recommend that a correction be made when estimating chest burns in women to account for the increased surface area of the breasts. A chart, such as the one we have developed, could be used in conjunction with a burn chart (e.g., Lund and Browder) to make this correction.     

The influence of load and leg amputation upon coordination in walking crustaceans: A model calculation

The following results were obtained by earlier authors when investigating the leg coordination of walking crustaceans (Decepoda): 1) After a leg is amputated, its stump moves in anti-phase with the next posterior intact leg. This corresponds to the coordination of intact animals. The stump, however, moves in-phase with the next anterior intact leg which contrasts with the coordination of intact animals (Clarac and Chasserat, 1979; Clarac, 1981). 2) Different results have been reported for the relation between the return stroke duration and step period: some authors found a significant dependency (e.g. MacMillan, 1975), others found none (e.g. Ayers and Davis, 1977). The calculation presented here shows, that these results can be described by a model incorporating the following assumptions: A) The forces developed by both, return stroke and power stroke muscles depend upon the load under which the leg walks. B) The influences which produce the coordinating effects found by Clarac and Chasserat for amputees also exist in intact animals and their strength depends upon the intensity of the motor output of the controlling leg. Within the model the selection of protraction or retraction is made at a “central unit” which calculates a value corresponding to the sum of graded inputs from several sources. The resulting fluctuation in this value might be considered analogous to graded oscillations recorded from central non-spiking interneurons. Qualitatively the model describes similar results obtained from insects.     

Influence of pelvis position on the activation of abdominal and hip flexor muscles

A pelvic position has been sought that optimizes abdominal muscle activation while diminishing hip flexor activation. Thus, the objective of the study was to investigate the effect of pelvic position and the Janda sit-up on trunk muscle activation. Sixteen male volunteers underwent electromyographic (EMG) testing of their abdominal and hip flexor muscles during a supine isometric double straight leg lift (DSLL) with the feet held approximately 5 cm above a board. The second exercise (Janda sit-up) was a sit-up action where participants simultaneously contracted the hamstrings and the abdominal musculature while holding an approximately 45 degrees angle at the knee. Root mean square surface electromyography was calculated for the Janda sit-up and DSLL under 3 pelvic positions: anterior, neutral, and posterior pelvic tilt. The selected muscles were the upper and lower rectus abdominis (URA, LRA), external obliques, lower abdominal stabilizers (LAS), rectus femoris, and biceps femoris. The Janda sit-up position demonstrated the highest URA and LRA activation and the lowest rectus femoris activation. The Janda sit-up and the posterior tilt were significantly greater (p < 0.01 and p < 0.05, respectively) than the anterior tilt for the URA and LRA muscles. Activation levels of the URA and LRA in neutral pelvis were significantly (p < 0.01 and p < 0.05, respectively) less than the Janda sit-up position, but not significantly different from the posterior tilt. No significant differences in EMG activity were found for the external obliques or LAS. No rectus femoris differences were found in the 3 pelvis positions. The results of this study indicate that pelvic position had a significant effect on the activation of selected trunk and hip muscles during isometric exercise, and the activation of the biceps femoris during the Janda sit-up reduced the activation of the rectus femoris while producing high levels of activation of the URA and LRA.     

Suspending loads decreases load stability but may slightly improve body stability

Here, we seek to determine how compliantly suspended loads could affect the dynamic stability of legged locomotion. We theoretically model the dynamic stability of a human carrying a load using a coupled spring-mass-damper model and an actuated spring-loaded inverted pendulum model, as these models have demonstrated the ability to correctly predict other aspects of locomotion with a load in prior work, such as body forces and energetic cost. We report that minimizing the load suspension natural frequency and damping ratio significantly reduces the stability of the load mass but may slightly improve the body stability of locomotion when compared to a rigidly attached load. These results imply that a highly-compliant load suspension could help stabilize body motion during human, animal, or robot load carriage, but at the cost of a more awkward (less stable) load.     

Interpersonal coordination analysis of tennis players from different levels during official matches

The purpose of this study was to assess the interpersonal coordination during official male tennis matches in players of different skill levels. Players’ trajectories of three levels (Juvenile, ATP-Future, ATP-250) were obtained using video-based tracking system. A vector coding technique was applied to obtain players’ interpersonal coordination in four coordination patterns: “anti-phase”, “in-phase”, “serving player phase” and “returning player phase”. These patterns allowed identification of the nature of the coupling and lead/lag relations between players. In all categories, players presented higher degree of “anti-phase” and “serving player phase” (when only the serving player is moving on the court or his opponent is moving with a time lag) coordination. Young players spent more time in “serving player phase” during lateral displacements than professional players. On the other hand, professional players spent more time in “returning player phase” (when only the returning player is moving on the court or his opponent is moving with a time lag) during antero posterior displacements, than young players. Interpersonal coordination did not change from the first to the second set of the match, showing that tennis players maintain their displacement characteristics and strategy, independently of proficiency level. The vector coding technique allowed to identify new coordination patterns in tennis, providing additional information about tennis dynamics and how players from different categories and proficiency levels behave during the matches.     

Use of a backpack alters gait initiation of high school students

We assessed how backpack carriage influences the gait initiation (GI) process in high school students, who extensively use backpacks. GI involves different dynamics from gait itself, while the excessive use of backpacks can result in adverse effects. 117 high school students were evaluated in three experimental conditions: no backpack (NB), bilateral backpack (BB), and unilateral backpack (UB). Two force plates were used to acquire ground reaction forces (GRFs) and moments for each foot separately. Center of pressure (COP) scalar variables were extracted, and statistical parametric mapping analysis was performed over the entire COP/GRFs time series. GI anticipatory postural adjustments (APAs) were reduced and were faster in backpack conditions; medial–lateral COP excursion was smaller in this phase. The uneven distribution of the extra load in the UB condition led to a larger medial–lateral COP shift in the support-foot unloading phase, with a corresponding vertical GRF change that suggests a more pronounced unloading swing foot/loading support foot mechanism. The anterior–posterior GRFs were altered, but the COP was not. A possible explanation for these results may be the forward trunk lean and the center of mass proximity of the base of support boundary, which induced smaller and faster APA, increased swing foot/support foot weight transfer, and increased load transfer to the first step.