An analysis of the effect of lower extremity strength on impact severity during a backward fall

Leg Joint Stiffness Affects Dynamics of Backward Falling From Standing Height: A Simulation Work

Falling backward can lead to injuries including hip fracture, back injury, and traumatic brain impact among older adults. A loss of consciousness is associated with falling backward and accounts for about 13% of all falls among older adults. Little is known about the dynamics of backward falls, such as the falling duration, the impact severity, and how the fall dynamics are affected by the biomechanical properties of the lower limb joints, particularly the rotational stiffness. The purpose of this study was to investigate the influence of the stiffness of individual leg joints on the dynamics of backward falls after losing consciousness in terms of the falling duration and impact velocities. Based on a 15-segment human model, we simulated the process of falling backward by sweeping the parameter space of ankle, knee, and hip's stiffnesses varying from 0 to 8.73 N·m·deg-1 (or 500 N·m·rad-1). The results revealed that the falling duration and impact speeds of the head and hip ranged from 0.27 to 0.63 s, 2.65 to 7.88 m·s-1, and 0.35 to 3.36 m·s-1, respectively, when the stiffness of the leg joints changed within their limits. Overall, the influence of the joint stiffness on the falling dynamics (falling duration and impact speed) is comparable between hip and knee joints, whereas ankle stiffness showed little influence on the backward falling dynamics. Our findings could provide references for designing protective devices to prevent impact-induced injuries after a backward fall.

Universal spectral profile and dynamic evolution of muscle activation: a hallmark of muscle type and physiological state

The skeletal muscle is an integrated multicomponent system with complex dynamics of continuous myoelectrical activation of various muscle types across time scales to facilitate muscle coordination among units and adaptation to physiological states. To understand the multiscale dynamics of neuromuscular activity, we investigated spectral characteristics of different muscle types across time scales and their evolution with physiological states. We hypothesized that each muscle type is characterized by a specific spectral profile, reflecting muscle composition and function, that remains invariant over time scales and is universal across subjects. Furthermore, we hypothesized that the myoelectrical activation and corresponding spectral profile during certain movements exhibit an evolution path in time that is unique for each muscle type and reflects responses in muscle dynamics to exercise, fatigue, and aging. To probe the multiscale mechanism of neuromuscular regulation, we developed a novel protocol of repeated squat exercise segments, each performed until exhaustion, and we analyzed differentiated spectral power responses over a range of frequency bands for leg and back muscle activation in young and old subjects. We found that leg and back muscle activation is characterized by muscle-specific spectral profiles, with differentiated frequency band contribution, and a muscle-specific evolution path in response to fatigue and aging that is universal across subjects in each age group. The uncovered universality among subjects in the spectral profile of each muscle at a given physiological state, as well as the robustness in the evolution of these profiles over a range of time scales and states, reveals a previously unrecognized multiscale mechanism underlying the differentiated response of distinct muscle types to exercise-induced fatigue and aging.NEW & NOTEWORTHY To understand coordinated function of distinct fibers in a muscle, we investigated spectral dynamics of muscle activation during maximal exercise across a range of frequency bands and time scales of observation. We discovered a spectral profile that is specific for each muscle type, robust at short, intermediate, and large time scales, universal across subjects, and characterized by a muscle-specific evolution path with accumulation of fatigue and aging, indicating a previously unrecognized multiscale mechanism of muscle tone regulation.

Studies on Practical Applications of Safe-Fall Control Strategies for Lower Limb Exoskeletons

Lower limb exoskeletons (LLEs) are susceptible to falls, and users are at risk of head and/or hip injuries. To address concerns regarding the safety of LLE users, optimization techniques were used to study safe-fall control strategies. Simulation results of these studies showed promising performance that leads to head impact avoidance and mitigation of hip impact velocity. The motivation for the current research was to extend the application of previously developed optimization techniques to study more realistic human-LLE fall conditions. We examined a range of feasible fall durations for the human-LLE model and found the optimal fall duration for which the user's safety is maximized. Next, we used a range of coefficients of friction to examine fall strategies on different ground surface conditions. We found that the effectiveness of a safe-fall strategy is higher when falling on less slippery surfaces compared to more slippery ones. The simulation results were implemented in a half-scale physical model of a three-link inverted pendulum, which represented a human-LLE model. Results of our experiments verified that the optimal safe-fall strategy could be implemented in a mechanical test setup. The hip linear velocity at impact was found to have similar values in both the experimental (2.04 m/s) and simulation results (2.09 m/s). Further studies should be conducted with appropriate software and hardware platforms to successfully implement safe-fall strategies in an actual LLE.

A multiscale model to predict current absolute risk of femoral fracture in a postmenopausal population

Osteoporotic hip fractures are a major healthcare problem. Fall severity and bone strength are important risk factors of hip fracture. This study aims to obtain a mechanistic explanation for fracture risk in dependence of these risk factors. A novel modelling approach is developed that combines models at different scales to overcome the challenge of a large space-time domain of interest and considers the variability of impact forces between potential falls in a subject. The multiscale model and its component models are verified with respect to numerical approximations made therein, the propagation of measurement uncertainties of model inputs is quantified, and model predictions are validated against experimental and clinical data. The main results are model predicted absolute risk of current fracture (ARF0) that ranged from 1.93 to 81.6% (median 36.1%) for subjects in a retrospective cohort of 98 postmenopausal British women (49 fracture cases and 49 controls); ARF0 was computed up to a precision of 1.92 percentage points (pp) due to numerical approximations made in the model; ARF0 possessed an uncertainty of 4.00 pp due to uncertainties in measuring model inputs; ARF0 classified observed fracture status in the above cohort with AUC = 0.852 (95% CI 0.753-0.918), 77.6% specificity (95% CI 63.4-86.5%) and 81.6% sensitivity (95% CI 68.3-91.1%). These results demonstrate that ARF0 can be computed using the model with sufficient precision to distinguish between subjects and that the novel mechanism of fracture risk determination based on fall dynamics, hip impact and bone strength can be considered validated.

Effects of Balance-Coordination, Strengthening, and Aerobic Exercises to Prevent Falls in Postmenopausal Patients With Osteoporosis: A 6-Month Randomized Parallel Prospective Study

Osteoporosis is a systemic disease characterized by the increase of bone fragility and fracture risk. Postmenopausal female osteoporotic patients were randomized into three groups: balance and coordination, strengthening, and aerobic exercise. The exercise programs were performed for 12 weeks, 1 hr each day for 3 days of the week. Patients were followed-up for 12 weeks after the initial intervention. After the exercise program, patients continued their daily life activities and were called back to the clinic for additional testing after 12 weeks. Static and dynamic balance measurements and pain and life quality assessments were performed at enrollment, and at the 12th and 24th weeks. Significant improvements in both the Timed Up and Go test and Berg Balance Scale values at the 12th week were only observed in the balance-coordination group. There were statistically significant improvements in night and daytime pain visual analog scale scores at the 12th and 24th weeks in the strengthening exercise group. No patient experienced falling during the 24th week follow-up. The strengthening exercises were observed to be more effective in pain reduction, and balance and coordination exercises were found to be more effective in improvement of static and dynamic balance.

Sideways fall-induced impact force and its effect on hip fracture risk: a review

Osteoporotic hip fracture, mostly induced in falls among the elderly, is a major health burden over the world. The impact force applied to the hip is an important factor in determining the risk of hip fracture. However, biomechanical researches have yielded conflicting conclusions about whether the fall-induced impact force can be accurately predicted by the available models. It also has been debated whether or not the effect of impact force has been considered appropriately in hip fracture risk assessment tools. This study aimed to provide a state-of-the-art review of the available methods for predicting the impact force, investigate their strengths/limitations, and suggest further improvements in modeling of human body falling.

METHODS

We divided the effective parameters on impact force to two categories: (1) the parameters that can be determined subject-specifically and (2) the parameters that may significantly vary from fall to fall for an individual and cannot be considered subject-specifically.

RESULTS

The parameters in the first category can be investigated in human body fall experiments. Video capture of real-life falls was reported as a valuable method to investigate the parameters in the second category that significantly affect the impact force and cannot be determined in human body fall experiments.

CONCLUSIONS

The analysis of the gathered data revealed that there is a need to develop modified biomechanical models for more accurate prediction of the impact force and appropriately adopt them in hip fracture risk assessment tools in order to achieve a better precision in identifying high-risk patients. Graphical abstract Impact force to the hip induced in sideways falls is affected by many parameters and may remarkably vary from subject to subject.

Developing safe fall strategies for lower limb exoskeletons

One of the main challenges in the use of a powered lower limb exoskeleton (LLE) is to ensure that balance is maintained throughout the operation of the device. Since no control strategy has yet been implemented that prevents falls in the case of a loss of balance, head or other serious injuries may occur during independent use of LLEs in the event of a fall. These safety concerns limit LLEs in the community to supervised use only. Using the backward fall as a model, we used optimization techniques to develop safe fall control strategies in order to avoid head impact and mitigate the impact velocity of the hips. From available human biomechanics data, we first developed an optimization methodology to study falls of healthy people. The results showed similar kinematic and dynamic characteristics to findings of previous studies on real-life human falls. Second, we extended the optimization methodology to include characteristics of a hypothetical LLE and to generate optimal joint trajectories and optimal torque profiles for the fall duration. The results revealed that by applying the optimal fall strategy, the severity of a simulated fall was minimized compared to when the device fell with locked joints (i.e., how currently used exoskeletons fall): head impact was avoided and hip impact velocity was reduced by more than 50%.

Can Recovery Foot Placement Affect Older Adults' Slip-Fall Severity?

Following a slip occurred in the overground walking, a fall can be classified into two exclusive categories: feet-forward fall or split fall. The purposes of this study were to investigate whether the placement of the recovery foot would determine the slip types, the likelihood of fall, and the severity associated with each fall. The fall severity was estimated based on the impact velocity of body segments or trunk orientation upon fall arrest. One hundred ninety-five participants experienced a novel, unannounced slip while walking on a 7-m walkway. Kinematics of a full-body marker set was collected by a motion capture system which was synchronized with the force plates and loadcell. The results showed that the recovery foot landing position relative to the projected center of mass position at the recovery foot touchdown determined the slip type by 90.8%. Feet-forward slips led to significantly lower rate of falls than did split slips (47.6 vs. 67.8%, p < 0.01). Yet, feet-forward falls were much more dangerous because they were associated with significantly greater estimated maximum hip impact velocity (p < 0.001) and trunk backward leaning angle (p < 0.001) in comparison to split falls.

Risk Factors for Traumatic Brain Injuries During Falls in Older Persons

OBJECTIVE

To identify risk factors for traumatic brain injuries (TBIs) during falls in older Taiwanese people.

PARTICIPANTS

Case patients consisted of 113 patients aged 60 years or older with a moderate/severe TBI due to a fall. Two control groups: (1) 339 older patients with a soft-tissue injury; and (2) 113 with a mild-TBI due to a fall. Proxies were required to provide information for a considerable number of patients.

DESIGN

Matched case-control study.

SETTINGS

The emergency departments of 3 general hospitals.

MEASURES

Sociodemographic, lifestyle behavior, chronic condition, medication use, functional abilities, and fall-related characteristics.

RESULTS

When patients with a soft-tissue injury were assigned to the control group, men were 2.06-fold more likely to have a moderate/severe TBI than women. Subjects who took antiarrhythmics within 4 hours of a fall were 2.59-fold more likely to have a moderate/severe TBI than those who took none. Subjects who were negotiating stairs and getting in/out of the bed/chair were 3.12-fold and 2.97-fold, respectively, more likely to have a moderate/severe TBI than those who fell while walking. Falling backward and sideways was 4.07-fold and 2.30-fold, respectively, more likely to cause a moderate/severe TBI than falling forward. When patients with a mild-TBI were assigned to the control group, results were similar, with the exception that the effect of antiarrhythmic use became nonsignificant and subjects who took 2 or more medications were 3.07-fold more likely to have a moderate/severe TBI than those who took none.

CONCLUSION

Avoiding a head impact during a backward or sideways fall, reducing unnecessary use of polypharmacy and antiarrhythmics, and maintaining safety during stair negotiation and bed/chair transfer may protect an elderly person from a severe brain injury.

Kinematics of judo breakfall for osoto-gari: Considerations for head injury prevention

Previous studies suggest that increasing the skill level of judokas will decrease the number of head injuries sustained during judo. However, the kinematics are poorly understood, making it difficult to establish an effective breakfall teaching programme. Therefore, we studied the kinematic parameters of breakfall for osoto-gari to identify the risk of judo-related head injuries by comparing experienced and novice judokas. This information will provide insight into developing a better prevention plan for judo-related head injuries. A total of 10 experienced and 12 novice judokas volunteered to participate in this study. The kinematic data of the breakfall motion for osoto-gari were collected using a three-dimensional motion analysis technique (200 Hz). We observed a significantly higher peak neck extension momentum in the novice group than in the experienced group. This suggests that neck extension momentum during breakfall is associated with the risk of head injuries during judo. In addition, the novice judokas demonstrated a significantly greater flexed pattern in the trunk and hip movement than the experienced judokas (P < 0.05). The results suggest that the trunk and lower extremity motion are important kinematic parameters that determine the skill level in performing the breakfall for osoto-gari.

Rationale for Strengthening Muscle to Prevent Falls and Fractures: A Review of the Evidence

Falls represent a major public health problem in older people, predominantly due to the resulting injuries which lead to progressive disability, immobilization and resulting comorbidities, dependency, institutionalization, and death. Reduced muscle strength and power have been consistently identified as risk factors for falls and related injuries, and it is likely these associations result from the central role played by reduced muscle strength and power in poor balance recovery. In addition, muscle strength and power are involved with protective responses that reduce the risk of an injury if a fall occurs. Progressive resistance training (PRT) is the standard way to increase muscle strength and power, and this training forms one of the main components of fall prevention exercise interventions. However, PRT has rarely been implemented in routine practice due to multiple challenges inherent to frail older people. The ongoing development of drugs expected to increase muscle power offers a new opportunity to reduce the risk of falls and fall-related injuries. The intent here is not to replace exercise training with drugs but rather to offer a pharmacologic alternative when exercise is not possible or contraindicated. The target population would be those most likely to benefit from this mechanism of action, i.e., weak older people without major causes for falls independent of muscle weakness. Provided such a tailored strategy was followed, a muscle anabolic may address this major unmet need.

Modulation and predictors of periprosthetic bone mineral density following total knee arthroplasty

Total knee arthroplasty (TKA) leads to a loss of periprosthetic bone mineral density (BMD). Great importance is attached to the prevention of periprosthetic bone loss with a view to ensuring a long service life of the prosthesis. In order to provide appropriate recommendations for preventive movement therapy measures to combat peri-implant bone loss, it is necessary to know the predictors of periprosthetic BMD. The aim of this study was (1) to determine the change of periprosthetic BMD of the femur and tibia and (2) to analyse the effects of different predictors on periprosthetic BMD. Twenty-three patients with primary TKA were evaluated 10 days and 3 months postoperatively. The data analysis comprised (1) the change in periprosthetic BMD from pretest to posttest and (2) the correlations between BMD and the variables isometric maximum voluntary force, lean mass, physical activity (step count), and BMI using multiple linear regression and structural equation modelling (SEM). BMD of the distal femur was significantly reduced by 19.7% (P = 0.008) 3 months after surgery, while no changes were found in BMD of the tibia. The results of SEM demonstrate that 55% of the BMD variance was explained by the model (χ² = 0.002; df = 1; P = 0.96; χ²/df = 0.002; RMSEA < 0.01; TLI = 1.5; CFI = 1.0). A significant direct effect was only evidenced by the variable lean mass (β = 0.38; b = 0.15; SE = 0.07; C.R. = 2.0; P = 0.046). It can be assumed that a large muscle mass with accompanying distribution of high mechanical load in the bones can contribute to local changes of periprosthetic BMD. Concrete recommendations for preventing peri-implant bone loss therefore include exercises which have the aim of maintaining or building up muscle mass.

Simple fall criteria for MEMS sensors: data analysis and sensor concept

This paper presents a new and simple fall detection concept based on detailed experimental data of human falling and the activities of daily living (ADLs). Establishing appropriate fall algorithms compatible with MEMS sensors requires detailed data on falls and ADLs that indicate clearly the variations of the kinematics at the possible sensor node location on the human body, such as hip, head, and chest. Currently, there is a lack of data on the exact direction and magnitude of each acceleration component associated with these node locations. This is crucial for MEMS structures, which have inertia elements very close to the substrate and are capacitively biased, and hence, are very sensitive to the direction of motion whether it is toward or away from the substrate. This work presents detailed data of the acceleration components on various locations on the human body during various kinds of falls and ADLs. A two-degree-of-freedom model is used to help interpret the experimental data. An algorithm for fall detection based on MEMS switches is then established. A new sensing concept based on the algorithm is proposed. The concept is based on employing several inertia sensors, which are triggered simultaneously, as electrical switches connected in series, upon receiving a true fall signal. In the case of everyday life activities, some or no switches will be triggered resulting in an open circuit configuration, thereby preventing false positive. Lumped-parameter model is presented for the device and preliminary simulation results are presented illustrating the new device concept.

Hip fracture and anthropometric variations: dominance among trochanteric soft tissue thickness, body height and body weight during sideways fall

BACKGROUND

Hip fracture depends on various anthropometric parameters such as trochanteric soft tissue thickness, body height and body weight. The objective was to evaluate the responses to the variations in anthropometric parameters during sideways fall, and to identify the most dominant parameter among them.

METHOD

Seven finite element models were developed having anthropometric variations in trochanteric soft tissue thickness (5-26 mm), body height (1.70-1.88 m), and body weight (63-93.37 kg). These were simulated for sideways fall with ANSYS-LS-DYNA® code.

FINDINGS

Significant effect of trochanteric soft tissue thickness variation was found on 'normalized peak impact force with respect to the body weight' (p=0.004, r²=0.808) and strain ratio (p=0.083, r²=0.829). But, variation in body height was found to be less significant on normalized peak impact force (p=0.478, r²=0.105) and strain ratio (p=0.292, r²=0.217). Same was true for the variation in body weight on normalized peak impact force (p=0.075, r²=0.456) and strain ratio (p=0.857, r²=0.007). The risk factor for fracture was also well correlated to the strain ratio for the inter-trochanteric zone (p<0.0007, r²=0.917) where the most fractures are clinically observed to happen.

INTERPRETATIONS

Trochanteric soft tissue thickness was found likely to be the most dominant parameter over body height and body weight, signifying that a slimmer elderly person, taller or shorter, with less trochanteric soft tissue thickness should be advised to take preventive measures against hip fracture under sideways fall.

Forward-backward postural protective stepping responses in young and elderly adults

OBJECTIVES

Protective steps are essential for fall avoidance. Most studies only examined forwards stepping despite considerable bio-mechanical and visual differences between the forwards and backwards directions. We assess forward-backward differences in protective steps in a young and elderly group.

METHODS

Protective stepping responses were elicited by a platform moving unpredictably either forwards or backwards. For control purposes, voluntary steps, in response to vibration cues on the forehead or occiput were also recorded. Reaction time (RT), length and angular velocity of the steps were measured in 13 young (age 19-35years) and 13 elderly (age 58-86years) healthy volunteers.

RESULTS

(i) Protective vs voluntary steps: protective steps were earlier, faster and longer than voluntary steps. (ii) Forwards-backwards differences: RT was quicker for backwards than forwards protective steps, in contrast to voluntary steps where RTs were similar in the two directions. (iii) Age difference: the elderly had universally slower steps and they generated shorter backwards than forwards protective steps.

CONCLUSIONS

Protective steps appear more robust than voluntary steps - they are earlier (shorter RT), longer and faster than voluntary steps, indicating an automatic rather than a volitional reaction. Backwards protective steps occur earlier than forwards; such promptness may have evolved out of bio-mechanical features which make falling backwards easier. Since our elderly subjects had an average age <70years, their slower and shorter protective backwards steps may represent the first abnormality in this rescue postural response. The findings in the elderly may partly depend on dysfunction in fronto-basal ganglia postural loops.

DXA and pQCT predict pertrochanteric and not femoral neck fracture load in a human side-impact fracture model

The validity of dual energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT) measurements as predictors of pertrochanteric and femoral neck fracture loads was compared in an experimental simulation of a fall on the greater trochanter. 65 proximal femora were harvested from patients at autopsy. All specimens were scanned with use of DXA for areal bone mineral density and pQCT for volumetric densities at selected sites of the proximal femur. A three-point bending test simulating a side-impact was performed to determine fracture load and resulted in 16 femoral neck and 49 pertrochanteric fractures. Regression analysis revealed that DXA BMD trochanter was the best variable at predicting fracture load of pertrochanteric fractures with an adjusted R(2) of 0.824 (p < 0.0001). There was no correlation between densitometric parameters and the fracture load of femoral neck fractures. A significant correlation further was found between body weight, height, femoral head diameter, and neck length on the one side and fracture load on the other side, irrespective of the fracture type. Clinically, the DXA BMD trochanter should be favored and integrated routinely as well as biometric and geometric parameters, particularly in elderly people with known osteoporosis at risk for falls.

Contribution of knee flexor and extensor strength on sex-specific energy absorption and torsional joint stiffness during drop jumping

CONTEXT

Lower extremity injury often occurs during abrupt deceleration when attempting to change the body's direction. Although sex-specific biomechanics have been implicated in the greater risk of acute knee injury in women than in men, it is unknown if sex differences in thigh strength affect sex-specific energy absorption and torsional joint stiffness patterns.

OBJECTIVE

To determine sex differences in energy absorption patterns and joint stiffnesses of the lower extremity during a drop jump and to determine if these sex differences were predicted by knee extensor and flexor strength.

DESIGN

Cross-sectional study.

SETTING

Laboratory environment.

PATIENTS OR OTHER PARTICIPANTS

Recreationally active, college-aged students (41 women: age  =  22.1 ± 2.9 years, height  =  1.63 ± 0.07 m, mass  =  59.3 ± 8.0 kg; 40 men: age  =  22.4 ± 2.8 years, height  =  1.77 ± 0.1 m, mass  =  80.9 ± 14.1 kg).

INTERVENTION(S)

Participants performed knee flexor and extensor maximal voluntary isometric contractions followed by double-leg drop-jump landings.

MAIN OUTCOME MEASURE(S)

Lower extremity joint energetics (J × N(-1) × m(-1)) and torsional joint stiffnesses (Nm × N(-1) × m(-1) × degrees(-1)) were calculated for the hip, knee, and ankle during the initial landing phase. Body weight was measured in newtons and height was measured in meters. Sex comparisons were made and sex-specific regressions determined if thigh muscle strength (Nm/kg) predicted sagittal-plane landing energetics and stiffnesses.

RESULTS

Women absorbed 69% more knee energy and had 36% less hip torsional stiffness than men. In women, greater knee extensor strength predicted greater knee energy absorption (R(2)  =  0.11, P  =  .04), and greater knee flexor strength predicted greater hip torsional stiffness (R(2)  =  0.12, P  =  .03).

CONCLUSIONS

Sex-specific biomechanics during the deceleration phase of a drop jump revealed that women used a strategy to attempt to decrease system stiffness. Additionally, only female strength values were predictive of landing energetics and stiffnesses. These findings collectively demonstrated that the task may have been more difficult for women, resulting in a different movement strategy among those with different levels of thigh strength to safely complete the task. Future researchers should look at other predictive factors of observed sex differences.

Physical activity and hip fracture disability: a review

Objective. The present paper examines pertinent literature sources published in the peer-reviewed English language between 1980 and November 1, 2010 concerning hip fractures. The aim was to highlight potential intervention points to offset the risk of incurring a hip fracture and its attendant disability. Methods. An in-depth search of the literature using the key terms: disability, epidemiology, hip fracture, prevention, and risk factors was conducted, along with data from the author's research base detailing the disability associated with selected hip fracture cases. All articles that dealt with these key topics were reviewed, and relevant data were tabulated and analyzed. Results. Hip fractures remain an important but potentially preventable public health problem. Among the many related remediable risk factors, low physical activity levels are especially important. Related determinants of suboptimal neuromuscular function also contribute significantly to hip fracture disability. Conclusion. Physical activity participation can help to reduce the prevalence and excess disability of hip fractures and should be encouraged.

Load on osseointegrated fixation of a transfemoral amputee during a fall: Determination of the time and duration of descent

Mitigation of fall-related injuries for populations of transfemoral amputees fitted with a socket or an osseointegrated fixation is challenging. Wearing a protective device fitted within the prosthesis might be a possible solution, provided that issues with automated fall detection and time of deployment of the protective mechanism are solved. The first objective of this study was to give some examples of the times and durations of descent during a real forward fall of a transfemoral amputee that occurred inadvertently while attending a gait measurement session to assess the load applied on the residuum. The second objective was to present five semi-automated methods of detection of the time of descent using the load data. The load was measured directly at 200 Hz using a six-channel transducer. The average time and duration of descent were 242 ± 42 ms (145-310 ms) and 619 ± 42 ms (550-715 ms), respectively. This study demonstrated that the transition between walking and falling was characterized by times of descent that occurred sequentially. The sensitivity and specificity of an automated algorithm might be improved by combining several methods of detection based on the deviation of the loads measured from their own trends and from a template previously established.

Hand grip strength: outcome predictor and marker of nutritional status

BACKGROUND & AIMS

Among all muscle function tests, measurement of hand grip strength has gained attention as a simple, non-invasive marker of muscle strength of upper extremities, well suitable for clinical use. This review outlines the prognostic relevance of grip strength in various clinical and epidemiologic settings and investigates its suitability as marker of nutritional status in cross-sectional as well as intervention studies.

METHODS

Studies investigating grip strength as prognostic marker or nutritional parameter in cross-sectional or intervention studies were summarized.

RESULTS AND CONCLUSIONS

Numerous clinical and epidemiological studies have shown the predictive potential of hand grip strength regarding short and long-term mortality and morbidity. In patients, impaired grip strength is an indicator of increased postoperative complications, increased length of hospitalization, higher rehospitalisation rate and decreased physical status. In elderly in particular, loss of grip strength implies loss of independence. Epidemiological studies have moreover demonstrated that low grip strength in healthy adults predicts increased risk of functional limitations and disability in higher age as well as all-cause mortality. As muscle function reacts early to nutritional deprivation, hand grip strength has also become a popular marker of nutritional status and is increasingly being employed as outcome variable in nutritional intervention studies.

Preservation of eccentric strength in older adults: Evidence, mechanisms and implications for training and rehabilitation

Overall reductions in muscle strength typically accompany the aging process. However, older adults show a relatively preserved capacity of producing eccentric strength. The preservation of eccentric strength in older adults is a well-established phenomenon, occurring indiscriminately across different muscle groups, independent of age-related architectural changes in muscle structure and velocity of movement. The mechanisms for the preservation of eccentric strength appear to be mechanical and cellular in origin and include both passive and active elements regulating muscle stiffness. The age-related accumulation of non-contractile material in the muscle-tendon unit increases passive stiffness, which might offer mechanical advantage during eccentric contractions. In addition, the preserved muscle tension and increased instantaneous stiffness of old muscle fibers during stretch increase active stiffness, which might enhance eccentric strength. The fact that the preservation of eccentric strength is present in people with chronic conditions when compared to age-matched healthy controls indicates that the aging process per se does not exclusively mediate the preservation of eccentric strength. Physical inactivity, which is common in elderly and people with chronic conditions, is a potential factor regulating the preservation of eccentric strength. When compared to concentric strength, the magnitude of preservation of eccentric strength in older adults ranges from 2% to 48% with a mean value of 21.6% from all studies. This functional reserve of eccentric strength might be clinically relevant, especially to initiate resistance training and rehabilitation programs in individuals with low levels of strength.

Load on osseointegrated fixation of a transfemoral amputee during a fall: loading, descent, impact and recovery analysis

Falling represents a health risk for lower limb amputees fitted with an osseointegrated fixation mainly because of the potential damage to the fixation. The purpose of this study was to characterize a real forward fall that occurred inadvertently to a transfemoral amputee fitted with an osseointegrated fixation while attending a gait measurement session to assess the load applied on the residuum. The objective was to analyze the load applied on the fixation with an emphasis on the sequence of events, the pattern and the magnitude of the forces and moments. The load was measured directly at 200 Hz using a six-channel transducer. Complementary video footage was also studied. The fall was divided into four phases: Loading (240 ms), descent (620 ms), impact (365 ms) and recovery (2495 ms). The main impact forces and moments occurred 870 ms and 915 ms after the heel contact, and corresponded to 133% BW and 17 % BWm, or 1.2 and 11.2 times the maximum forces and moments applied during the previous steps of the participant, respectively. This study provided key information to engineers and clinicians facing the challenge to design equipment, and rehabilitation and exercise programs to restore safely the locomotion of lower limb amputees.

Is Tai Chi Chuan effective in improving lower limb response time to prevent backward falls in the elderly?

To evaluate the training effect of Tai Chi Chuan (TCC) in postural control and backward fall prevention in the elderly, balance assessment and visually guided lower limb response time were analyzed in a case-control study conducted in a community setting. Thirty-one elderly subjects (mean age: 68.2 +/- 6.8 years) participated in the TCC group, 30 community-dwelling elderly subjects with matched age and body composition served as the elderly control group, with 13 young adults (mean age: 27.5 +/- 3.8 years) serving as young controls. The TCC group had practiced TCC regularly five times per week, for over 30 min per day for at least 4 years. Lower limb response time were measured using a computerized dance machine that we developed, which contains two blocks during testing: single and dual feet. The motor planning of the latter is more complex than the former. Postural control was assessed by computerized posturography (Smart Balance Master). Compared to the elderly controls, the TCC group demonstrated significantly better balance performance in sway-referenced support, which is more challenging. Moreover, the TCC group had better dual feet response than the elderly controls in the forward-backward, forward-right and forward-left directions. Practicing TCC may improve motor responses and postural control in the elderly, particularly in more challenging situations. Subjects showed better postural responses to unexpected perturbation in the forward-backward and forward-sideways direction than sideways or backward-sideways directions, which may have clinical relevance.

Cortical and trabecular bone in the femoral neck both contribute to proximal femur failure load prediction

We examined the contributions of femoral neck cortical and trabecular bone to proximal femur failure load. We found that trabecular bone mineral density explained a significant proportion of variance in failure load after accounting for total bone size and cortical bone mineral content or cortical area.

INTRODUCTION

The relative contribution of femoral neck trabecular and cortical bone to proximal femur failure load is unclear.

OBJECTIVES

Our primary objective was to determine whether trabecular bone mineral density (TbBMD) contributes to proximal femur failure load after accounting for total bone size and cortical bone content. Our secondary objective was to describe regional differences in the relationship among cortical bone, trabecular bone, and failure load within a cross-section of the femoral neck.

MATERIALS AND METHODS

We imaged 36 human cadaveric proximal femora using quantitative computed tomography (QCT). We report total bone area (ToA), cortical area (CoA), cortical bone mineral content (CoBMC), and TbBMD measured in the femoral neck cross-section and eight 45 degrees regions. The femora were loaded to failure.

RESULTS AND OBSERVATIONS

Trabecular bone mineral density explained a significant proportion of variance in failure load after accounting for ToA and then either CoBMC or CoA respectively. CoBMC contributed significantly to failure load in all regions of the femoral neck except the posterior region. TbBMD contributed significantly to failure load in all regions of the femoral neck except the inferoanterior, superoposterior, and the posterior regions.

CONCLUSION

Both cortical and trabecular bone make significant contributions to failure load in ex vivo measures of bone strength.

Muscle mass is more strongly related to hip bone mineral density than is quadriceps strength or lower activity level in adults over age 50 year

This cross-sectional study examined whether reduced hip bone mineral density (BMD) is better explained by isokinetic knee extensor strength (KES), lower limb lean body mass (L-LBM), or Physical Activity Scale for the Elderly (PASE). Through population-based recruitment, 1543 adults without knee osteoarthritis were recruited. For men and women respectively, means+/-SD were age 60.8+/-8.0 and 61.1+/-7.9 yr; body mass index 29.6+/-4.6 and 29.1+/-5.4 kg/m(2); hip BMD 1.025+/-0.138 and 0.895+/-0.128 g/cm(2); KES 124.9+/-41 and 72.7+/-22.9 N.m; L-LBM 10.3+/-1.5 and 7.0+/-1.2 kg; and PASE 206.4+/-99.7 and 163.8+/-77.0. The relationship between BMD and KES in men (r(2)=0.21, p> or =0.002) and women (r=0.23, p<0.001) was significant before adjustment. However, this association was no longer significant after controlling for L-LBM. Even after controlling for age, race, and sex, the association between BMD and KES was better explained by L-LBM (partial R(2)=0.14, p<0.001) than by PASE (partial R(2)=0.00). Allometric scaling of KES to body size attenuated the association of BMD with KES (Std Beta=0.03). The significant association between BMD and L-LBM (Std Beta=0.36) remained stronger than that between BMD and weight (Std Beta=0.21). Therefore, muscle mass accounted for a greater proportion of the variance in hip BMD than KES or activity level and explained a significant proportion of the association between weight and BMD.

Effect of soft shell hip protectors on pressure distribution to the hip during sideways falls

INTRODUCTION

While hip protectors represent a promising strategy for preventing hip fractures, clinical efficacy has been limited by poor user compliance. Soft shell protectors may be more acceptable to users than traditional hard shell designs. However, before embarking on clinical trials to assess efficacy, laboratory experiments are required to determine how soft shell protectors affect the force applied during impact to the hip. This was the goal of the current study.

METHODS

Fifteen women participated in "pelvis release experiments," which safely simulate the impact stage of a sideways fall. During the trials, we measured total impact force and mean pressure over the greater trochanter with the participant unpadded, and while wearing two commercially available soft shell protectors.

RESULTS

Mean pressure over the greater trochanter was reduced by 76% by a 14-mm thick horseshoe-shaped protector and by 73% by a 16-mm thick continuous protector. Total force was reduced by 9% by the horseshoe and by 19% by the continuous protector.

CONCLUSIONS

Soft shell hip protectors substantially reduce the pressure over the greater trochanter, while only modestly reducing total impact force during simulated sideways falls. These data support the need for clinical trials to determine whether soft shell protectors reduce hip fracture risk in vulnerable populations.

Effect of Upper and Lower Extremity Control Strategies on Predicted Injury Risk During Simulated Forward Falls: A Study in Healthy Young Adults

Fall-related wrist fractures are common at any age. We used a seven-link, sagittally symmetric, biomechanical model to test the hypothesis that systematically alterations in the configuration of the body during a forward fall from standing height can significantly influence the impact force on the wrists. Movement of each joint was accomplished by a pair of agonist and antagonist joint muscle torque actuators with assigned torque-angle, torque-velocity, and neuromuscular latency properties. Proportional-derivative joint controllers were used to achieve desired target body segment configurations in the pre- and∕or postground contact phases of the fall. Outcome measures included wrist impact forces and whole-body kinetic energy at impact in the best, and worst, case impact injury risk scenarios. The results showed that peak wrist impact force ranged from less than 1kN to more than 2.5kN, reflecting a fourfold difference in whole-body kinetic energy at impact (from less than 40J to more than 160J) over the range of precontact hip and knee joint angles used at impact. A reduction in the whole-body kinetic energy at impact was primarily associated with increasing negative work associated with hip flexion. Altering upper extremity configuration prior to impact significantly reduced the peak wrist impact force by up to 58% (from 919Nto2212N). Increased peak wrist impact forces associated greater shoulder flexion and less elbow flexion. Increasing postcontact arm retraction can reduce the peak wrist impact force by 28% (from 1491Nto1078N), but postcontact hip and knee rotations had a relatively small effect on the peak wrist impact force (8% reduction; from 1411Nto1303N). In summary, the choice of the joint control strategy during a forward fall can significantly affect the risk of wrist injury. The most effective strategy was to increase the negative work during hip flexion in order to dissipate kinetic energy thereby reducing the loss in potential energy prior to first impact. Extended hip or elbow configurations should be avoided in order to reduce forearm impact forces.

Effect of pre-impact movement strategies on the impact forces resulting from a lateral fall

Approximately 90% of hip fractures in older adults result from falls, mostly from landing on or near the hip. A three-dimensional, 11-segment, forward dynamic biomechanical model was developed to investigate whether segment movement strategies prior to impact can affect the impact forces resulting from a lateral fall. Four different pre-impact movement strategies, with and without using the ipsilateral arm to break the fall, were implemented using paired actuators representing the agonist and antagonist muscles acting about each joint. Proportional-derivative feedback controller controlled joint angles and velocities so as to minimize risk of fracture at any of the impact sites. It was hypothesized that (a) the use of active knee, hip and arm joint torques during the pre-contact phase affects neither the whole body kinetic energy at impact nor the peak impact forces on the knee, hip or shoulder and (b) muscle strength and reaction time do not substantially affect peak impact forces. The results demonstrate that, compared with falling laterally as a rigid body, an arrest strategy that combines flexion of the lower extremities, ground contact with the side of the lower leg along with an axial rotation to progressively present the posterolateral aspects of the thigh, pelvis and then torso, can reduce the peak hip impact force by up to 56%. A 30% decline in muscle strength did not markedly affect the effectiveness of that fall strategy. However, a 300-ms delay in implementing the movement strategy inevitably caused hip impact forces consistent with fracture unless the arm was used to break the fall prior to the hip impact.

Fragile external phenotype of modern human proximal femur in comparison with medieval bone

Proximal femur macroanatomy of 118 medieval and 67 contemporary adults, 84 contemporary elderly, and 48 contemporary hip fracture cases was evaluated. Within approximately 1000 years, the femoral neck axis has become longer, and its cross-section has become proportionally smaller and more oval in shape. These changes in the present external phenotype alone account for approximately 50% higher fall-induced stress compared with the medieval situation.

INTRODUCTION

Bones, as whole skeletal structures, adapt to mechanical stresses they customarily experience. Because the present, mechanized lifestyle apparently deprives our skeletons of vigorous, habitual physical exertion, we studied whether the proximal femur phenotype has evolved vulnerable to fragility fractures by time.

MATERIALS AND METHODS

Proximal femur macroanatomy of 118 medieval and 67 contemporary adults, 84 contemporary elderly, and 48 contemporary hip fracture cases was evaluated. Using direct measurements of external bone dimensions and geometric properties, we estimated the fall-induced stress as an index of hip fragility.

RESULTS

Within approximately 1000 years, the femoral axis length has become substantially longer (analysis of covariance, body height adjusted, p < 0.001), whereas the neck circumference has not increased. The macroanatomy was found similar between the contemporary adult and elderly groups. In hip fracture cases, however, the femoral axis length was further lengthened (p < 0.001), but the circumference was somewhat smaller (p = 0.001). Consequently, the estimated fall-induced stress can be approximately 1.5-fold today compared with the medieval times (p < 0.001), and the secular trend seemed to be worse in women (sex-time interaction, p = 0.001).

CONCLUSIONS

The modern, relatively slender phenotype of the proximal femur alone seems to increase the fall-induced stress considerably, and when this phenotype coincides the osteoporotic, internally deteriorated femoral neck structure, fracture risk is imminent. This mechanically compromised external phenotype underscores the importance of timely strengthening of the skeleton and its regular maintenance throughout life.

Martial arts fall techniques decrease the impact forces at the hip during sideways falling

Falls to the side and those with impact on the hip are risky for hip fractures in the elderly. A previous study has indicated that martial arts (MA) fall techniques can reduce hip impact force, but the underlying mechanism is unknown. Furthermore, the high impact forces at the hand used to break the fall have raised concerns because of the risk for wrist fractures. The purpose of the study was to get insight into the role of hand impact, impact velocity, and trunk orientation in the reduction of hip impact force in MA techniques. Six experienced judokas performed sideways falls from kneeling height using three fall techniques: block with arm technique (control), MA technique with use of the arm to break the fall (MA-a), and MA technique without use of the arm (MA-na). The results showed that the MA-a and MA-na technique reduced the impact force by 27.5% and 30%, respectively. Impact velocity was significantly reduced in the MA falls. Trunk orientation was significantly less vertical in the MA-a falls. No significant differences were found between the MA techniques. It was concluded that the reduction in hip impact force was associated with a lower impact velocity and less vertical trunk orientation. Rolling after impact, which is characteristic for MA falls, is likely to contribute to the reduction of impact forces, as well. Using the arm to break the fall was not essential for the MA technique to reduce hip impact force. These findings provided support for the incorporation of MA fall techniques in fall prevention programs for elderly.

The Effect of Aging on the Backward Stepping Reaction as Estimated from the Velocity of Center of Foot Pressure and Muscular Strength

By estimating the deflection velocity from the center of foot pressure (COP), this study aims to prove that the characteristics of the backward stepping reaction in the elderly are related to the strength of the antigravity muscles. The participants in this study were 10 elderly (average age 75.6+/-7.6 years) and 13 young (average age 22.0+/-2.6 years) subjects. Using force plate analysis, we measured the shift in the deflection velocity (V-RMS) and the maximum deflection velocity (V-MAX) from the beginning of the COP movement to the onset of the stepping reaction. Furthermore, we measured the strength of the antigravity muscles using a hand-held dynamometer. We correlated the V-RMS, V-MAX, and the rate of change of the deflection velocity (MAX/RMS) with muscular strength. When compared with the young subjects, the elderly showed significantly lower values of V-RMS (p<0.05) and significantly higher values of MAX/RMS (p<0.01). Furthermore, when compared with the young subjects, the elderly showed significantly lower values of muscular strength for all muscles studied (p<0.001). We established a significant correlation between the V-RMS, MAX/RMS, and muscular strength by carrying out a regression analysis (V-RMS: gluteus maximus (r=0.50, p<0.05) and rectus abdominis (r=0.48, p<0.05); MAX/RMS: adductor magnus (r=-0.66, p<0.001) and flexor digitorum longus (r=-0.62, p<0.01)). Differences were observed in the V-RMS and MAX/RMS during the backward stepping reaction; it was proposed that these differences were related to the age and muscular strength of the subjects. Therefore, further investigations should be undertaken in order to understand the effects of aging on the stepping reaction. In other words, the change-in-support strategy, including the preparatory phase of the stepping reaction, and its relationship with muscular strength should be further investigated.

Deficient limb support is a major contributor to age differences in falling

Older adults are more likely than young to fall upon a loss of balance, yet the factors responsible for this difference are not well understood. This study investigated whether age-related differences in movement stability, limb support, and protective stepping contribute to the greater likelihood of falling among older adults. Sixty young and 41 older, safety-harnessed, healthy adults were exposed to a novel and unexpected forward slip during a sit-to-stand task. More older than young adults fell (76% vs. 30%). Falls in both age groups were related to lesser stability and lower hip height at first step touchdown, with 97.1% of slip outcomes correctly classified based on these variables. Decreases in hip height at touchdown had over 20 times greater effect on the odds of falling than equivalent decreases in stability. Three age differences placed older adults at greater risk of falling: older adults had lower and more slowly rising hips at slip onset, they were less likely to respond to slipping with ample limb support, and they placed their stepping foot less posterior to their center of mass. The first two differences, each associated with deficient limb support, reduced hip ascent and increased hip descent. The third difference resulted in lesser stability at step touchdown. These results suggest that deficient limb support in normal movement patterns and in the reactive response to a perturbation is a major contributor to the high incidence of falls in older adults. Improving proactive and reactive limb support should be a focus of fall prevention efforts.

Wrist impact velocities are smaller in forward falls than backward falls from standing

The wrist is a common fracture site for both young and older adults. The purpose of this study was to compare wrist kinematics in backward and forward falls with different fall protective responses. We carried out within-subject comparison of impact velocities and maximum velocities during descent of the distal radius among three different fall configurations: (a) backward falls with knees flexed, (b) backward falls with knees extended and (c) forward falls with knees flexed. We also examined the effect of fall configuration on fall durations, elbow flexion, trunk flexion and forearm angles at impact. Forward falls resulted in smaller impact velocities of the distal radius, longer fall duration, longer braking duration, greater elbow flexion and more horizontal landing position of the forearm compared to backward falls. The distal radius impact velocity during forward falls (1.33 m/s) was significantly lower than in backward falls, and among the backward falls the impact velocity of the flexed knee strategy (2.01 m/s) was significantly lower than the extended knee strategy (2.27 m/s). These impact velocities were significantly reduced from the maximum velocities observed during descent (forward falls=3.57 m/s, backward falls with knee flexed=3.16 m/s, backward falls with knees extended=3.52 m/s). We conclude that (1) smaller impact velocities of the wrists in forward falls could imply a lower fracture risk compared to backward falls, and (2) fall protective responses reduced wrist impact velocities in all fall directions.

Effect of the "squat protective response" on impact velocity during backward falls

Risk for injury during a fall depends on the position and velocity of the body segments at the moment of impact. One technique for reducing impact velocity is to absorb energy in the lower extremity muscles during descent, as occurs during squatting or sitting. However, the protective value of this response may depend on the time during descent when the response is initiated. We tested this hypothesis by conducting backward falling experiments with young women (n = 23; aged 21-29 years), who fell onto a soft gymnasium mattress after being suddenly releasing from an inclined position. In trials where subjects were released from a 5 degrees lean, average impact velocities were reduced by 18% when squatting was utilized as opposed to inhibited. Furthermore, increases in the release angle caused an increase in average impact velocity of 8% between lean angles of 2 degrees and 5 degrees, and 7% between lean angles of 5 degrees and 12 degrees. This was due to declines in peak extensor torques and peak flexion rotations, and corresponding reductions in both joint work and potential energy at impact. These results suggest that squatting during descent reduces impact severity, but the effectiveness of the response depends on the stage during descent when it is initiated, diminishing in benefit as the fall progresses and the state of imbalance grows increasingly severe.

Hip fractures among the elderly: causes, consequences and control

This review examines all pertinent literature sources published in the English language between 1966 to the present concerning hip fracture epidemiology, hip fracture injury mechanisms, and hip fracture management strategies. These data reveal hip fractures have several causes, but among these, the impact of falls and muscle weakness, along with low physical activity levels seems to be the most likely explanation for the rising incidence of hip fracture injuries. Related determinants of suboptimal nutrition, drugs that increase fall risk and lower the safety threshold and comorbid conditions of the neuromuscular system may also contribute to hip fracture disability. A number of interventions may help to prevent hip fracture injuries, including, interventions that optimize bone mass and quality, interventions that help prevent falls and falls dampening interventions. Rehabilitation outcomes may be improved by comprehensive interventions, prolonged follow-up strategies and ensuring that all aging adults enjoy optimal health.