Greater Loading Rates Research Articles

Evaluation of select biochars and clays as supports for phytase to increase the fertilizer potential of animal wastes

Manures may contain considerable amounts of organophosphates (org-P) that must be enzymatically converted to inorganic phosphate (i.e., PO4-P) to be plant available. Although adding enzymes into manures can facilitate mineralization of org-P to PO4-P, enzymes that are not immobilized are easily lost through leaching, degradation, or denaturation. In this study, the immobilization of enzymes onto nine different biochar surfaces was explored. Phytase, which mineralizes a main class of org-P, was used as the model enzyme. Immobilization methods included covalent grafting accomplished by the carbodiimide crosslinker method and physical sorption. The results showed that physisorption was as effective as grafting for loading phytase to the biochars. Phytase loading after mixing 0.1 g biochar and 2 mg phytase correlated positively with biochar C:H ratio (an indicator of aromatic content) suggesting the importance of the hydrophobic effect. An increase in pH led to a decrease in phytase loading consistent with repulsion between negatively charged sites on phytase and the increasing negative charge on biochar. Less than 4% of the immobilized phytase leached after sequential extractions over seven days using manure dissolve organic matter solutions. However, the activity of immobilized phytase decreased markedly compared to the free state phytase. The specific activity of immobilized phytase was two orders of magnitude lower than that of free phytase at pH 5 and 7. Nevertheless, results showed that deactivation of phytase by biochars were reversible once the phytase was detached from the surfaces. Compared to the biochars, clay minerals (montmorillonite, kaolinite and hematite) tended to have greater loading rates and higher phytase activity. Composting manures with coamendments of biochar and minerals may enhance both short- and long-term P mineralization potential.

A kinetic analysis of the triple step in recreational swing dancers

ABSTRACT Despite its increasing popularity, swing dancing has not been fully studied biomechanically, imposing challenges in understanding the movement patterns associated with swing dancing. The purpose of this study was to examine the biomechanics of the triple step, one of the most common swing dance elements. We intended to determine whether dancing with a partner affects kinetic measurements and if these measurements are different among the three steps. Eight recreational swing dancers completed three triple steps to the right and the left with and without a partner. The loading rate of the vertical ground reaction force was calculated for each step, and bilateral lower limb joints moments and powers were determined. Results illustrated that dancing with or without a partner has limited effect on the kinetic measurements. However, the outcome measurements differed among the steps: a higher peak vertical ground reaction force during the first and second steps, a greater loading rate during the second step, and the greatest joint power absorption at the ankle and knee during the second step were observed. The findings extend our understanding of the biomechanics of swing dancing, and could provide preliminary guidance for understanding swing dance-related injuries and improving performance of swing dancing.

Explosive Quadriceps Strength and Landing Mechanics in Females with and without Anterior Cruciate Ligament Reconstruction.

Lower explosive quadriceps strength, quantified as rate of torque development (RTD), may contribute to landing mechanics associated with anterior cruciate ligament (ACL) injury risk. However, the association between quadriceps RTD and landing mechanics during high demand tasks remains unclear. Therefore, this study investigated the influence of quadriceps RTD on sagittal plane landing mechanics during double-leg jump landings (DLJL) and single-leg jump cuts (SLJC) in females with and without ACL reconstruction (ACLR). Quadriceps RTD was measured during isometric muscle contractions. Landing mechanics were collected during DLJL and SLJC tasks. Separate stepwise multiple linear regression models determined the amount of variance in sagittal plane landing mechanics that could be explained by quadriceps RTD, group (ACLR or Control), and their interaction. The results indicate that greater quadriceps RTD is associated with lower loading rate (p = 0.02) and longer time to peak vertical ground reaction force (p = 0.001) during SLJC, regardless of ACLR status. As greater loading rate may lead to higher risk of ACL injuries and post-traumatic knee osteoarthritis post-ACLR, explosive muscle strength interventions might be useful for individuals with and without ACLR to facilitate the use of safer landing mechanics.

Vibration improves gait biomechanics linked to posttraumatic knee osteoarthritis following anterior cruciate ligament injury.

Anterior cruciate ligament reconstruction (ACLR) incurs a high risk of posttraumatic knee osteoarthritis (PTOA). Aberrant gait biomechanics contribute to PTOA and are attributable in part to quadriceps dysfunction. Vibration improves quadriceps function following ACLR, but its effects on gait biomechanics are unknown. The purpose of this study was to evaluate the effects of whole-body vibration (WBV) and local muscle vibration (LMV) on gait biomechanics in individuals with ACLR. Seventy-five volunteers (time since ACLR 27 ± 16 months) were randomized to WBV, LMV, or Control interventions. Walking biomechanics were assessed prior to and following a single exposure to the interventions. Outcomes included pre-post change scores in the ACLR limb for the peak vertical ground reaction force (vGRF) and its loading rate, peak internal knee extension (KEM) and abduction moments, and peak knee flexion and varus angles. LMV produced a significant decrease in the vGRF loading rate (-3.6 BW/s) that was greater than the changes in the WBV (-0.3 BW/s) and Control (0.5 BW/s) groups. Additionally, WBV produced an increase in the peak KEM (0.27% BW × Ht) that was greater than the change in the Control group (-0.17% BW × Ht) but not the LMV group (0.01% BW × Ht). Lower KEM and greater loading rates have been linked to declines in joint health following ACLR. WBV acutely increased the peak KEM and LMV decreased loading rates. These data suggest that vibration has the potential to mitigate aberrant gait biomechanics, and may represent an effective approach for reducing PTOA risk following ACLR.

Gait Biomechanics Linked To Post-traumatic Osteoarthritis Following Anterior Cruciate Ligament Reconstruction Are Improved With Vibration

PURPOSE: Anterior cruciate ligament reconstruction (ACLR) incurs a high risk of post-traumatic knee osteoarthritis (PTOA). Aberrant gait biomechanics contribute to PTOA and are attributable in part to quadriceps dysfunction. Vibration improves quadriceps function following ACLR, but its effects on gait biomechanics are unknown. The purpose of this study was to evaluate the effects of whole body vibration (WBV) and local muscle vibration (LMV) on gait biomechanics in individuals with ACLR. METHODS: 75 volunteers with primary unilateral ACLR (72% females; age 21 ± 3 yr; time since ACLR 27 ± 16 mo) were randomized to WBV, LMV, or Control interventions. WBV and LMV were applied 6 x 1 minute (30Hz, 2g). Walking biomechanics were assessed prior to and following the interventions. Outcomes included the peak vertical ground reaction force (vGRF) and its loading rate, peak internal knee extension and valgus moments, and peak knee flexion and varus angles during the first 50% of stance. vGRF magnitude and rate were normalized to body weight (BW) and moments were normalized as % body weight∗height (%BW∗Ht). ACLR limb change scores (post-pre) for each outcome were compared across groups via one-way ANCOVA controlling for gait speed, time since ACLR, and baseline values. RESULTS: Change scores did not differ across groups for peak knee flexion (p = 0.374) or varus (p = 0.801) angles, vGRF (p = 0.656), or internal valgus moment (p = 0.866). However, changes in vGRF loading rate differed across groups (p = 0.024), with a significant decrease in the LMV group (-3.6 BW/s) that was greater than the changes in the WBV (-0.3 BW/s; p = 0.035) and Control (0.5 BW/s; p = 0.010) groups. Additionally, the change in peak internal extension moment differed across groups (p = 0.016), with a significant increase in the WBV group (0.27 %BW∗Ht) that was greater than the change in the Control group (-0.17 %BW∗Ht; p = 0.005) but not the LMV group (0.01 %BW∗Ht; p = 0.101). CONCLUSIONS: Lower knee extension moments and greater loading rates during gait have been linked to declines in joint health following ACLR. WBV acutely increased the peak knee extension moment and LMV decreased loading rates. These data suggest that vibration has the potential to mitigate aberrant gait biomechanics, and may represent an effective approach for mitigating PTOA risk following ACLR.

A 6-Week Transition to Maximal Running Shoes Does Not Change Running Biomechanics

Background: A recent study suggested that maximal running shoes may increase the impact force and loading rate of the vertical ground-reaction force during running. It is currently unknown whether runners will adapt to decrease the impact force and loading rate over time. Purpose: To compare the vertical ground-reaction force and ankle kinematics between maximal and traditional shoes before and after a 6-week acclimation period to the maximal shoe. Study Design: Controlled laboratory study. Methods: Participants ran in a traditional running shoe and a maximal running shoe during 2 testing sessions 6 weeks apart. During each session, 3-dimensional kinematics and kinetics were collected during overground running. Variables of interest included the loading rate, impact peak, and active peak of the vertical ground-reaction force, as well as eversion and dorsiflexion kinematics. Two-way repeated measures analyses of variance compared data within participants. Results: No significant differences were observed in any biomechanical variable between time points. The loading rate and impact peak were higher in the maximal shoe. Runners were still everted at toe-off and landed with less dorsiflexion, on average, in the maximal shoe. Conclusion: Greater loading rates and impact forces were previously found in maximal running shoes, which may indicate an increased risk of injury. The eversion mechanics observed in the maximal shoes may also increase the risk of injury. A 6-week transition to maximal shoes did not significantly change any of these measures. Clinical Relevance: Maximal running shoes are becoming very popular and may be considered a treatment option for some injuries. The biomechanical results of this study do not support the use of maximal running shoes. However, the effect of these shoes on pain and injury rates is unknown.

Individuals Post Achilles Tendon Rupture Exhibit Asymmetrical Knee and Ankle Kinetics and Loading Rates During a Drop Countermovement Jump.

Study Design Cross-sectional laboratory study. Background Asymmetrical knee loading during jogging and hopping has been reported in individuals who have ruptured their Achilles tendon. No studies have examined knee loads in individuals post Achilles tendon rupture during high-demand tasks, such as single-limb landings. Objectives We sought to determine whether individuals post Achilles tendon rupture demonstrated asymmetrical knee loads and impact forces during drop countermovement jumps (CMJs). Methods Achilles tendon length and the single-leg heel-rise test for endurance were assessed in 34 individuals (31 male) 6.1 ± 2.0 years post Achilles tendon rupture. Movement patterns were assessed during a drop CMJ. Data were analyzed via repeated-measures analyses of variance, with comparisons between limbs and prior treatment history (surgery versus nonsurgery). Results An 8.6% longer Achilles tendon (P<.001) was found in the involved limb. During the single-leg heel-rise test, the involved limb demonstrated 22.4% less endurance and 14.6% lower heel-rise height (all, P<.001). During the landing phase of the drop CMJ, the involved limb exhibited 39.6% greater loading rate (P<.001), 16.8% greater eccentric knee power (P = .048), but 21.6% lower eccentric ankle power (P<.001). During the take-off phase, the involved limb exhibited 12.1% lower jump height and 19.9% lower concentric ankle power (both, P<.001). Conclusion Elevated eccentric knee joint power and higher loading rates during a drop CMJ in individuals who experienced Achilles tendon rupture several years earlier may be a compensation pattern for reduced plantar flexor function. This movement pattern may place individuals who have had an Achilles tendon rupture at greater risk for knee injuries. J Orthop Sports Phys Ther 2018;48(1):34-43. Epub 26 Oct 2017. doi:10.2519/jospt.2018.7684.

Achilles Tendon Load is Progressively Increased with Reductions in Walking Speed.

Achilles tendon rehabilitation protocols commonly recommend a gradual increase in walking speed to progressively intensify tendon loading. This study used transmission-mode ultrasound to evaluate the influence of walking speed on loading of the human Achilles tendon in vivo. Axial transmission speed of ultrasound was measured in the right Achilles tendon of 33 adults (mean ± SD: age, 29 ± 3 yr; height, 1.725 ± 0.069 m; weight, 71.4 ± 19.9 kg) during unshod, steady-state treadmill walking at three speeds (slow, 0.85 ± 0.12 ms; preferred, 1.10 ± 0.13 m·s; fast, 1.35 ± 0.20 m·s). Ankle kinematics, spatiotemporal gait parameters and vertical ground reaction force were simultaneously recorded. Statistical comparisons were made using repeated-measures ANOVA models. Increasing walking speed was associated with higher cadence, longer step length, shorter stance duration, greater ankle plantarflexion, higher vertical ground reaction force peaks, and a greater loading rate (P < 0.05). Maximum (F1,38 = 7.38, P < 0.05) and minimum (F1,46 = 8.95, P < 0.05) ultrasound transmission velocities in the Achilles tendon were significantly lower (16-23 m·s) during the stance but not swing phase of gait, with each increase in walking speed. Despite higher vertical ground reaction forces and greater ankle plantarflexion, increasing walking speed resulted in a reduction in the axial transmission velocity of ultrasound in the Achilles tendon; indicating a speed-dependent reduction in tensile load within the triceps surae muscle-tendon unit during walking. These findings question the rationale for current progressive loading protocols involving the Achilles tendon, in which reduced walking speeds are advocated early in the course of treatment to lower Achilles tendon loads.

Inter-limb differences in impulsive loading following anterior cruciate ligament reconstruction in females

Anterior cruciate ligament injury and reconstruction (ACLR) dramatically increase the risk of knee osteoarthritis, but the contributing factors, and therefore the targets for intervention, are poorly understood. Differences in loading characteristics between the ACLR and contralateral limbs during routine activities such as walking may elucidate the mechanical pathogenesis of post-traumatic knee osteoarthritis. Twenty-nine females with ACLR (age=21.7±3.1 years; time since ACL injury=48±41 months) performed walking gait at a self-selected speed from which the overall peak vertical ground reaction force (vGRF) in the first 50% of the stance phase and its linear (slope of the vGRF-time curve) and instantaneous (first time-derivative) loading rates were calculated. The magnitude of the vGRF peak immediately following heelstrike and its linear and instantaneous loading rates were also identified. Subjects were further classified as “Impulsive Loaders” or “Normal Loaders” based on whether the transient vGRF peak immediately following heelstrike was objectively classified as a heelstrike transient in the majority of trials. The vGRF magnitude immediately following heelstrike and instantaneous loading rates (both overall and immediately following heelstrike) were greater in the ACLR limb. Additionally, vGRF linear and instantaneous loading rates were greater in subjects classified as Impulsive Loaders. As higher loading rates are associated with greater cartilage degradation in animal models, these data suggest that the greater loading rates in the ACLR limb may play an important role in development of post-traumatic knee osteoarthritis. Additionally, the heelstrike transient appears to be an objective indicator of impulsive loading.

Jump Landings On Land And In Waist-Deep Water

Current research on aquatic jump training has focused on performance benefits in younger, not older, participants. Aquatic jump training may be particularly beneficial for middle-age and older adults given its low impact nature and focus on power and stability, which are often compromised with aging. It is unclear if the same aquatic jumping benefits (e., reduced impact forces) observed in younger adults applies to middle-age adults. PURPOSE: To compare landing kinetics and dynamic stability between young and middle-age adults performing jumping movements on land and in water. METHODS: Ten young (age = 24 ± 2.6 yrs) and ten middle-age (age = 47 ± 3.0 yrs) adults performed three jump variations (countermovement jump, squat jump, and drop landing) on land and in waist-deep water. Dynamic stability was assessed during landing using a time to stabilization (TTS) paradigm. Kinetic measures included time to peak force, peak force, rate of force development (RFD), and impulse. Data were collected via a waterproof force platform positioned on an adjustable-depth pool floor. Data were analyzed using a 2 (environment) X 2 (age) X 3 (jump type) ANOVA. RESULTS: Regardless of age and jump type, TTS was greater (p = 0.02) on land (1.42 ± 0.12s) than in water (1.34 ± 0.13s). Peak force, RFD, and impulse followed this same trend and were greater on land than in water (p < 0.01). Time to peak force for the middle-age group (0.07 s) was lower (p = 0.001), while normalized peak force (4.4 BW) and RFD (74 BW/s) were greater (p < 0.05) than values for the young group (0.08 s, 3.8 BW, and 53 BW/s, respectively) regardless of environment or jump type. CONCLUSION: Regardless of age or jump type, TTS was lower in water suggesting greater dynamic stability in this environment. Additionally, participants displayed lower impact forces in water suggesting this environment might be safer than land when performing jump training. Across environments, middle-age participants landed with greater loading rates and peak forces when compared to the younger group.

Ankle and knee kinetics between strike patterns at common training speeds in competitive male runners

The purpose of this study was to investigate the interaction of foot strike and common speeds on sagittal plane ankle and knee joint kinetics in competitive rear foot strike (RFS) runners when running with a RFS pattern and an imposed forefoot strike (FFS) pattern. Sixteen competitive habitual male RFS runners ran at two different speeds (i.e. 8 and 6 min mile−1) using their habitual RFS and an imposed FFS pattern. A repeated measures analysis of variance was used to assess a potential interaction between strike pattern and speed for selected ground reaction force (GRF) variables and, sagittal plane ankle and knee kinematic and kinetic variables. No foot strike and speed interaction was observed for any of the kinetic variables. Habitual RFS yielded a greater loading rate of the vertical GRF, peak ankle dorsiflexor moment, peak knee extensor moment, peak knee eccentric extensor power, peak dorsiflexion and sagittal plane knee range of motion compared to imposed FFS. Imposed FFS yielded greater maximum vertical GRF, peak ankle plantarflexor moment, peak ankle eccentric plantarflexor power and sagittal plane ankle ROM compared to habitual RFS. Consistent with previous literature, imposed FFS in habitual RFS reduces eccentric knee extensor and ankle dorsiflexor involvement but produce greater eccentric ankle plantarflexor action compared to RFS. These acute differences between strike patterns were independent of running speeds equivalent to typical easy and hard training runs in competitive male runners. Current findings along with previous literature suggest differences in lower extremity kinetics between habitual RFS and imposed FFS running are consistent among a variety of runner populations.

An unstable rocker-bottom shoe alters lower extremity biomechanics during level walking

Biomechanical data for gait in unstable rocker bottom shoes reported in the literature is not comprehensive across available shoe types. Purpose: The objective of this study was to comprehensively evaluate centre of pressure (COP), ground reaction force (GRF), joint kinematics and kinetics, and electromyography (EMG) of selected muscles while walking in an unstable shoe compared to a control shoe. Methods: Fifteen subjects performed five walking trials at 1.3 m/s and 1.8 m/s in control and unstable shoes. Kinematic, GRF and EMG data were simultaneously collected. Results: The unstable shoe caused an increased mediolateral COP displacement. Greater loading rate of initial peak vertical GRF, reduced ankle plantarflexion range of motion (ROM) and greater total sagittal-plane ankle ROM were also observed for the unstable shoe compared to the control shoe. Peak dorsiflexion and plantarflexion moments, peak knee flexion moment as well as EMG activation of tibialis anterior and rectus femoris were reduced in the unstable shoe. Finally, the peak inversion moment and hip abduction moment were increased in the unstable shoe. Conclusion: These results suggest that the unstable shoe presents challenges to the body to maintain mediolateral stability and therefore helps improve involved ankle and hip muscles. Furthermore the demands for the lower extremity muscles related to the sagittal-plane motions were reduced in the unstable shoe.

Impact Characteristics of Female Children Running in Adult Versus Youth Shoes of the Same Size

The purpose of this study was to determine if ground reaction forces were influenced by shoe design (adult vs. youth) for female children when running. Subjects (n = 10, 12.0 ± 1.1 years old; 154 ± 4.9 cm; 46.2 ± 14.3 kg; shoe size 3.5-7 youth) were fit with a shoe model available in youth and adult sizes. Subjects ran 10 trials per shoe condition across a force platform placed in the middle of a 9-m runway. Impact force, second maximum force, loading rate, stance time and average vertical ground reaction forces were recorded for each trial. Shoes underwent a mechanical impact test with peak force, peak acceleration, and percent energy returned recorded. Each variable was compared between shoe conditions. From the impact testing, it was determined that peak force, peak acceleration and percent energy return were 7.1%, 7.1%, and 18.9% greater, respectively, for the youth vs. adult shoe (p < .001). From the running tests, it was determined that loading rate was different (p = .009) between shoe conditions whereas impact force, second maximum force, average force and stance time were not different between shoes (p > .01). Young girls had a greater loading rate when running in youth vs. adult shoes even though the shoe size was the same.

Adolescents after pemberton's osteotomy for developmental dysplasia of the hip displayed greater joint loading than healthy controls in affected and unaffected limbs during gait

Patients after reduced developmental dysplasia of the hip (DDH) are at higher than normal risk of developing avascular necrosis (AVN) of the femoral head and degenerative hip osteoarthritis (OA) that are closely related to abnormal loadings. We aimed to determine the lower limb loadings in adolescents after Pemberton's osteotomy for unilateral DDH. Eleven females (age: 10.6 ± 1.0 years), who had received Pemberton's osteotomy for unilateral DDH at 1.6 ± 0.5 years of age, and 12 age-matched healthy controls were studied using gait analysis. Compared to the normal controls, the patients were displayed greater peak axial forces at the hip, knee, and ankle in both limbs, with greater loading rates in the ground reaction force (GRF) and at the hips (p < 0.05 for all comparisons). The increased rates of repetitive loading around heel strike in both hips suggest that patients treated for unilateral DDH using Pemberton's osteotomy may be at higher risk of premature hip OA. The increased axial forces at the affected hip may be a contributing factor to the development of AVN of the femoral head in these patients, especially when incomplete coverage, insufficient congruency, and/or damaged articular surfaces remain after the osteotomy. Therefore, monitoring the loading condition at the hip is necessary for a more accurate assessment of the risk of developing joint pathology in patients after reduced DDH.