Joint power and kinematics coordination in load carriage running: Implications for performance and injury

Investigating the impact of incremental load magnitude on running joint power and kinematics is important for understanding the energy cost burden and potential injury-causative mechanisms associated with load carriage. It was hypothesized that incremental load magnitude would result in phase-specific, joint power and kinematic changes within the stance phase of running, and that these relationships would vary at different running velocities. Thirty-one participants performed running while carrying three load magnitudes (0%, 10%, 20% body weight), at three velocities (3, 4, 5 m/s). Lower limb trajectories and ground reaction forces were captured, and global optimization was used to derive the variables. The relationships between load magnitude and joint power and angle vectors, at each running velocity, were analyzed using Statistical Parametric Mapping Canonical Correlation Analysis. Incremental load magnitude was positively correlated to joint power in the second half of stance. Increasing load magnitude was also positively correlated with alterations in three dimensional ankle angles during mid-stance (4.0 and 5.0 m/s), knee angles at mid-stance (at 5.0 m/s), and hip angles during toe-off (at all velocities). Post hoc analyses indicated that at faster running velocities (4.0 and 5.0 m/s), increasing load magnitude appeared to alter power contribution in a distal-to-proximal (ankle → hip) joint sequence from mid-stance to toe-off. In addition, kinematic changes due to increasing load influenced both sagittal and non-sagittal plane lower limb joint angles. This study provides a list of plausible factors that may influence running energy cost and injury risk during load carriage running.     

Influence of fatigue and load carriage on mechanical loading during walking

Load carriage and muscular fatigue are two major stressors experienced by military recruits during basic training. The purpose of this study was to assess the influences of load carriage and muscular fatigue on ground reaction forces and ground reaction loading rates during walking. Eighteen healthy males performed the following tasks in order: unloaded and unfatigued walking, loaded and unfatigued walking, fatiguing exercise, loaded and fatigued walking, and unloaded and fatigued walking. The fatiguing exercise consisted of a series of metered step-ups and heel raises with a 16-kg rucksack. Loaded walking tasks were performed with a 32-kg rucksack. Two-way repeated measures analysis of variances were used to determine the effects of fatigue and load carriage on ground reaction forces and loading rates. Muscular fatigue has a significant influence on peak vertical ground reaction force and loading rate (p < 0.01). Load carriage has a significant influence on peak ground reaction forces and loading rates (p < 0.001). As both muscular fatigue and load carriage lead to large increases of ground reaction forces and loading rates, the high incidence of lower extremity overuse injuries in the military may be associated with muscular fatigue and load carriage.     

Effects of load carriage on biomechanical variables associated with tibial stress fractures in running

BackgroundMilitary personnel are required to run while carrying heavy body-borne loads, which is suggested to increase their risk of tibial stress fracture. Research has retrospectively identified biomechanical variables associated with a history of tibial stress fracture in runners, however, the effect that load carriage has on these variables remains unknown.Research questionWhat are the effects of load carriage on running biomechanical variables associated with a history of tibial stress fracture?MethodsTwenty-one women ran at 3.0 m/s on an instrumented treadmill in four load carriage conditions: 0, 4.5, 11.3, and 22.7 kg. Motion capture and ground reaction force data were collected. Dependent variables included average loading rate, peak absolute free moment, peak hip adduction, peak rearfoot eversion, and stride frequency. Linear mixed models were used to asses the effect of load carriage and body mass on dependent variables.ResultsA load x body mass interaction was observed for stride frequency only (p = 0.017). Stride frequency increased with load carriage of 22.7-kg, but lighter participants illustrated a greater change than heavier participants. Average loading rate (p < 0.001) and peak free moment (p = 0.015) were greater in the 22.7-kg condition, while peak rearfoot eversion (p ≤ 0.023) was greater in the 11.3- and 22.7-kg conditions, compared to the unloaded condition. Load carriage did not affect peak hip adduction (p = 0.67).SignificanceParticipants adapted to heavy load carriage by increasing stride frequency. This was especially evident in lighter participants who increased stride frequency to a greater extent than heavier participants. Despite this adaptation, running with load carriage of ≥11.3-kg increased variables associated with a history of tibial stress fracture, which may be indicative of elevated stress fracture risk. However, the lack of concomitant change amongst variables as a function of load carriage may highlight the difficulty in assessing injury risk from a single measure of running biomechanics.     

The relationships between multiaxial loading history and tibial strains during load carriage

Objectives

To determine if a history of exercise involving multiaxial loading, through soccer participation, influences tibial stains during incremented load carriage.

Uncontrolled manifold analysis of gait variability: effects of load carriage and fatigue

The uncontrolled manifold (UCM) analysis has been demonstrated to be a powerful tool for understanding motor variability. The purpose of this study was to use the UCM analysis to investigate the effects of load carriage and fatigue on gait variability. Whole-body kinematic data during treadmill walking were collected from 12 healthy male participants when fatigue and load carriage were applied. The task-level variable for the UCM analysis was selected to be the whole-body COM. We chose to analyze the whole-body COM data at two important gait events: right heel contact and right toe off, and the UCM analysis was carried out in the sagittal and frontal planes, separately. The dependent measures were UCM variability measures and UCM ratio. Three-way ANOVA was performed to determine the main and interaction effects of back-carrying load, fatigue, and gait events on the dependent measures. The results showed that frontal UCM ratio significantly changed with the application of back-carrying load and fatigue, indicating that both factors had effects on motor performance in stabilizing the whole-body COM in the frontal plane. These findings can facilitate a better understanding of the nature of motor variability due to load carriage and fatigue.     

Soldier load carriage: historical, physiological, biomechanical, and medical aspects

This study reviews historical and biomedical aspects of soldier load carriage. Before the 18th century, foot soldiers seldom carried more than 15 kg while on the march, but loads have progressively risen since then. This load increase is presumably due to the weight of weapons and equipment that incorporate new technologies to increase protection, firepower, communications, and mobility. Research shows that locating the load center of mass as close as possible to the body center of mass results in the lowest energy cost and tends to keep the body in an upright position similar to unloaded walking. Loads carried on other parts of the body result in higher energy expenditures: each kilogram added to the foot increases energy expenditure 7% to 10%; each kilogram added to the thigh increases energy expenditure 4%. Hip belts on rucksacks should be used whenever possible as they reduce pressure on the shoulders and increase comfort. Low or mid-back load placement might be preferable on uneven terrain but high load placement may be best for even terrain. In some tactical situations, combat load carts can be used, and these can considerably reduce energy expenditure and improve performance. Physical training that includes aerobic exercise, resistance training targeted at specific muscle groups, and regular road marching can considerably improve road marching speed and efficiency. The energy cost of walking with backpack loads increases progressively with increases in weight carried, body mass, walking speed, or grade; type of terrain also influences energy cost. Predictive equations have been developed, but these may not be accurate for prolonged load carriage. Common injuries associated with prolonged load carriage include foot blisters, stress fractures, back strains, metatarsalgia, rucksack palsy, and knee pain. Load carriage can be facilitated by lightening loads, improving load distribution, optimizing load-carriage equipment, and taking preventive action to reduce the incidence of injury.     

The distribution of forces between the upper and lower back during load carriage

INTRODUCTION/PURPOSE: To determine the effects of backpack mass on the forces exerted by the backpack on the carrier and on the distribution of these forces between the upper back (including shoulders) and lower back (sacrum and iliac crest). METHODS: Eleven male volunteers (mean age 22.7 SEM 1.1 yr) walked on a level treadmill at 1.34 m.s(-1) carrying a backpack loaded to three different masses (13.6, 27.2, and 40.8 kg). The backpack's hip belt was connected to force transducers that measured the forces exerted on the lower back. The total force between the subject and backpack was determined from the backpack's mass and acceleration. Forces on the upper back were calculated as total force minus the forces exerted on the lower back. RESULTS: There was a significant effect of backpack mass on the vertical and anterior/posterior forces exerted on the upper and lower back, and on the total force exerted on the backpack center of mass. Regardless of mass, approximately 30% of the vertical force was borne by the lower back; the upper back and shoulders supported the remaining 70%; this is based on data averaged across the stride. Dimensionless analysis revealed peak forces on the upper and lower back increased proportionately to backpack mass whereas the peak forces exerted on the backpack COM increased disproportionately. CONCLUSIONS: The backpack exerts consistent anterior force on the lower back, which likely contributes to the occurrence of low-back pain associated with load carriage. Approximately 30% of the vertical force generated by the backpack can be transferred to the lower back by using an external frame backpack with a hip belt.     

Temporal relationship between trunk and thigh contributes to balance control in load carriage walking

Load carriage walking (LCW) challenges a person's balance as the load increases their forward trunk inclination, shifting the center of mass (COM) forward with respect to the base of support (BOS). We examined LCW to understand whether and how healthy people adjust the temporal relationship (TR) between the trunk and leg for balance control. Ten subjects were recruited to perform unloaded walking and LCW. The TR between the trunk and leg was measured by the continuous relative phase. The maximum forward displacement of the COM with respective to the BOS (FDCOM_BOS) was recorded during the stance phase. We found that the TR was shifted in LCW, and the shift was associated with a decrease in the maximum FDCOM_BOS. The findings suggest that the TR between the trunk and leg contributes to balance control, and it may be a variable that needs to be addressed in gait rehabilitation.     

Effects of prolonged load carriage on angular jerk of frontal and sagittal knee motion

BackgroundDuring training, service members routinely walk with heavy body borne loads for long periods of time. These loads alter knee biomechanics and may produce jerky knee motions that reportedly increase joint loading and risk of musculoskeletal injury. Yet, it is unknown if service members use jerky knee motions during prolong walking with body borne load.Research questionTo quantify the effects of body borne load and duration of walking on the jerkiness of sagittal and frontal plane knee motion.MethodsEighteen participants had angular jerk of knee motion quantified while they walked (1.3 m/s) for 60-min with three body borne loads (0, 15, and 30 kg). Peak and cost of angular jerk for sagittal and frontal plane knee motion was quantified and submitted to a repeated measures linear model to test the main effects and interaction of load (0, 15, and 30 kg) and time (0, 15, 30, 45, and 60 min).ResultsBody borne load increased peak and cost of angular jerk for sagittal plane knee motion up to 35 % and 110 %, respectively, and frontal plane knee motion up to 20 % and 51 %, respectively (all p<0.001), while jerk cost of frontal plane knee motion (p=0.001) increased 31 % after walking 45 min.SignificanceBody borne load produced large (between 20 % and 110 %), incremental increases in angular jerk for both sagittal and frontal plane knee motion; whereas, duration of walking led to a 31 % increase in jerkiness of frontal plane knee motion. Service members who often walking for long periods of time with heavy body borne loads may have greater risk of developing musculoskeletal injury and disease due to large increases in jerky knee motions.     

Effects of load carriage and footwear on lower extremity kinetics and kinematics during overground walking

Kinetic and kinematic responses during walking vary by footwear condition. Load carriage also influences gait patterns, but it is unclear how an external load influences barefoot walking. Twelve healthy adults (5 women, 7 men) with no known gait abnormalities participated in this study (age = 23 ± 3 years, height = 1.73 ± 0.11 m, and mass = 70.90 ± 12.67 kg). Ground reaction forces and 3D motion were simultaneously collected during overground walking at 1.5 m s⁻¹ in four conditions: Barefoot Unloaded, Shod Unloaded, Barefoot Loaded, and Shod Loaded. Barefoot walking reduced knee and hip joint ranges of motion, as well as stride length, stance time, swing time, and double support time. Load carriage increased stance and double support times. The 15% body weight load increased GRFs ∼15%. Walking barefoot reduced peak anteroposterior GRFs but not peak vertical GRFs. Load carriage increased hip, knee, and ankle joint moments and powers, while walking barefoot increased knee and hip moments and powers. Thus, spatiotemporal and kinematic adjustments to walking barefoot decrease GRFs but increase knee and hip kinetic measures during overground walking. The ankle seems to be less affected by these footwear conditions. Regardless of footwear, loading requires larger GRFs, joint loads, and joint powers.     

An alternative whole-body marker set to accurately and reliably quantify joint kinematics during load carriage

Body armor covers anatomical landmarks that would otherwise be used to track trunk and pelvis movement in motion analysis. This study developed and evaluated a new marker set, and compared it to placing markers on the skin and over-top of body armor. In our method, pelvis and trunk motions were measured using a custom-built sacral and upper-back marker cluster, respectively. Joint angles and ranges of motion were determined while participants walked without and with body armor. Angles were obtained from the new marker set and compared against conventional marker sets placed on the skin or over-top the body armor. Bland-Altman analyses compared the agreement of kinematic parameters between marker sets, while joint angle waveforms were compared using inter-protocol coefficient of multiple correlations (CMCs). The intra- and inter-session similarities of joint angle waveforms from each marker set were also assessed using CMCs. There was a strong agreement between joint angles from the new marker set and markers placed directly on the skin at key anatomical landmarks. The agreement worsened with markers placed on top of body armor. Inter-protocol CMCs comparing markers on body armor to the new marker set were poor compared to CMCs between skin-mounted markers and the new marker set. Intra- and inter-session repeatability were higher for the new marker set compared to placing markers over-top of body armor. The new marker set provides a viable alternative for researchers to reliably measure trunk and pelvis motion when equipment, such as body armor, obscures marker placement.     

A contaminated binormal model for ROC data: Part III. Initial evaluation with detection ROC data

RATIONALE AND OBJECTIVES: The authors' purpose was to evaluate how well the contaminated binormal receiver operating characteristic (ROC) model fits (a) degenerate data for which standard ROC models commonly fail and (b) nondegenerate data from exemplary experiments, for which the standard binormal model should be appropriate. MATERIALS AND METHODS: The authors studied two examples of binormally degenerate data, with and without interior points, and ROC rating data from four experiments in visual psychophysics and radiology. The plots of contaminated binormal ROC curves of the binormal degenerate data were examined. For ROC data with at least one interior point, the new model was compared with conventional models on the basis of likelihood-ratio chi2 statistics (G2). RESULTS: With no interior points, the contaminated binormal model gave results consistent with the fundamental principle underlying ROC analysis, that is, for a fixed false-positive probability, the higher the true-positive probability, the better the diagnostic performance. Contaminated binormal ROC curves go through the empirical ROC points of the degenerate data without crossing the chance line or climbing far above the true-positive fractions of the points. For several model ROC studies, the contaminated binormal model gave smaller G2 results than conventional ROC models, although the differences tended to be small, usually with little difference in ROC area. CONCLUSION: The contaminated binormal model fits binormal degenerate data better than conventional ROC models, and it offers an explanation for the degeneracy. The lower G2 values on some classic, nondegenerate ROC data suggest that contamination may not be limited to degenerate ROC data.     

Load carriage energy expenditure with and without hiking poles during inclined walking

The purpose of this study was to compare load carriage energy expenditure with and without using hiking poles. Twenty male volunteers aged 20-48yr (Mean=29.8yr) completed two randomly ordered submaximal treadmill trials with poles (E) and without poles (C). Poles and load (15 kg backpack) were fitted for each subject according to the manufacturers' suggestions. Heart rates (HR), minute ventilation (V(E)), oxygen consumption (O2), caloric expenditure (Kcal), and rating of perceived exertion (RPE) were recorded at the end of each minute. Two trials separated by one week consisted of a constant treadmill speed of 1.5 mph and 1 min at 10% grade, 2 min at 15% grade, 2 min at 20% grade, and 10 min. at 25% grade. Mean HR (E = 144.8 +/- 24.4 b x min(-1); C = 144.0 +/- 25.7 b x min(-1)) and mean V(E) (E=51.4 +/- 15.8L x min(-1); C=50.8 +/- 17.0L x min(-1)), VO2 (E = 26.9 +/- 6.1 ml x kg(-1) x min(-1); C = 27.4 +/- 6.6 ml x kg(-1) x min(-1)), and Kcal (E = 10.6 +/- 2.9 Kcal x min(-1); C = 10.8 +/- 3.1 Kcal x min(-1)) were not significantly different between the two conditions. RPE (E = 13.28 +/- 1.2; C = 14.56 +/- 1.2) was significantly lower (P < 0.05) with hiking poles. Analysis of paired time points yielded no significant differences in HR, VO2, V(E), and Kcal, however, RPE means were significantly lower for 5 of the last 7 trial minutes with the use of poles. These results suggest that during load carriage on moderate grade, the weight and use of hiking poles does not increase energy expenditure but may provide reduced perceptions of physical exertion.     

Initial experience with lung-MRI at 3.0T: Comparison with CT and clinical data in the evaluation of interstitial lung disease activity

OBJECTIVES: We evaluated the feasibility of highfield lung-MRI at 3.0T. A comparison with Computed Tomography (CT) and clinical data regarding the assessment of inflammatory activity in patients with diffuse lung disease was performed. MATERIAL AND METHODS: Prospective evaluation of 21 patients (15 males, 6 females, 43-80 y) with diffuse lung diseases who underwent clinical work-up inclusive laboratory tests, lung-function tests and transbronchial biopsy. After routine helical CT (additional 12 HRCT) a lung-MRI (3.0 Intera, Philips Medical Systems, Best, The Netherlands) using a T2-weighted, cardiac and respiratory triggered Fast-Spinecho-Sequence (TE/TR=80/1500-2500 ms, 22 transverse slices, 7/2mm slice-thickness/-gap) was performed. A pneumologist classified the cases into two groups: A=temporary acute interstitial disease or chronic interstitial lung disease with acute episode or superimposed infection/B=burned out interstitial lung disease without activity. Two blinded CT-radiologists graded the cases in active/inactive disease on the basis of nine morphological criteria each. A third radiologist rated the MRI-cases as active/inactive, depending on the signal-intensities of lung tissues. RESULTS: The pneumologist classified 14 patients into group A and 7 patients into group B. Using CT, 6 cases were classified as active, 15 cases as inactive disease. With MRI 12 cases were classified as active and 9 cases as inactive. In the complete group of 21 patients MRI decisions and CT decisions respectively were false positive/false negative/correct in 2/4/15 respectively 0/8/13 cases. Correct diagnoses were obtained in 72% (MRI) respectively 62% (CT). In the subgroup of 12 cases including HRCT, MRI respectively CT were false positive/false negative/correct in 2/1/9 respectively 0/5/7 cases. Correct diagnoses were obtained in 75% (MRI) respectively 58% (CT). CONCLUSION: Highfield MRI of the lung is feasible and performed slightly better compared to CT in the determination of activity in patients with interstitial lung diseases.     

Balance in single-limb stance in patients with anterior cruciate ligament injury: relation to knee laxity, proprioception, muscle strength, and subjective function

BACKGROUND: It has been shown previously that an anterior cruciate ligament injury may affect postural control, measured by balance in single-limb stance. To our knowledge, no studies have reported the influence of measures of impairment on postural control after such an injury. PURPOSE: To assess the influence of knee laxity, proprioception, and muscle strength on balance in single-limb stance and to study the correlation between balance in single-limb stance and subjective estimation of extremity function. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A total of 36 patients with a unilateral, nonoperated, nonacute anterior cruciate ligament injury were examined with regard to anterior knee laxity, proprioception, muscle strength, and stabilometry (amplitude and average speed of the center of pressure movements). Subjective estimation of extremity function was measured on a visual analog scale. RESULTS: The multiple regression analysis showed that high knee laxity values were associated with high amplitude values and low average speed. Poor proprioception and high muscle strength values were associated with low average speed among the women only. Low amplitude values correlated with better subjective function. CONCLUSION: Anterior knee laxity, proprioception, and muscle strength seem to play a role in maintaining balance in single-limb stance. Patients with low amplitude values in stabilometry were those with better subjective function.     

Objective and subjective comparison of standard 2-D and fully 3-D reconstructed data on a PET/CT system

OBJECTIVE: The relative advantage of fully 3-D versus 2-D mode for whole-body imaging is currently the focus of considerable expert debate. The nature of 3-D PET acquisition for FDG PET/CT theoretically allows a shorter scan time and improved efficiency of FDG use than in the standard 2-D acquisition. We therefore objectively and subjectively compared standard 2-D and fully 3-D reconstructed data for FDG PET/CT on a research PET/CT system. MATERIALS AND METHODS: In a total of 36 patients (mean 58.9 years, range 17.3-78.9 years; 21 male, 15 female) referred for known or suspected malignancy, FDG PET/CT was performed using a research PET/CT system with advanced detector technology with improved sensitivity and spatial resolution. After 45 min uptake, a low-dose CT (40 mAs) from head to thigh was performed followed by 2-D PET (emission 3 min per field) and 3-D PET (emission 1.5 min per field) with both seven slices overlap to cover the identical anatomical region. Acquisition time was therefore 50% less (seven fields; 21 min vs. 10.5 min). PET data was acquired in a randomized fashion, so in 50% of the cases 2-D data was acquired first. CT data was used for attenuation correction. 2-D (OSEM) and 3-D PET images were iteratively reconstructed. Subjective analysis of 2-D and 3-D images was performed by two readers in a blinded, randomized fashion evaluating the following criteria: sharpness of organs (liver, chest wall/lung), overall image quality and detectability and dignity of each identified lesion. Objective analysis of PET data was investigated measuring maximum standard uptake value with lean body mass (SUV(max,LBM)) of identified lesions. RESULTS: On average, per patient, the SUV(max) was 7.86 (SD 7.79) for 2-D and 6.96 (SD 5.19) for 3-D. On a lesion basis, the average SUV(max) was 7.65 (SD 7.79) for 2-D and 6.75 (SD 5.89) for 3-D. The absolute difference on a paired t-test of SUV 3-D-2-D based on each measured lesion was significant with an average of -0.956 (P=0.002) and an average of -0.884 on a patient base (P<0.05). With 3-D the SUV(max) decreased by an average of 5.2% for each lesion, and an average of 6.0% for each patient. Subjective analysis showed fair inter-observer agreement regarding detectability (kappa=0.24 for 3-D; 0.36 for 3-D) and dignity (kappa=0.44 for 3-D and 0.4 for 2-D) of the lesions. There was no significant diagnostic difference between 3-D and 2-D. Only in one patient, a satellite liver metastasis of a colon cancer was missed in 3-D and detected only in 2-D. On average, the overall image quality for 3-D images was equal (in 24%) or inferior (in 76%) compared to 2-D. CONCLUSION: A possible major advantage of 3-D data acquisition is the faster patient throughput with a 50% reduction in scan time. The fully 3-D reconstruction technique has overcome the technical drawbacks of current 3-D imaging technique. In our limited number of patients there was no significant diagnostic difference between 2-D and fully 3-D.