Biomedical subjects

Kermit G Davis

Publications and source records attributed to Kermit G Davis.

12 recordsLinked to original sources

PubMed2006

Postural balance changes in on-duty firefighters: effect of gear and long work shifts.

OBJECTIVE: The objective of this study was to investigate the impact of long work shifts and turnout gear, including the self-contained breathing apparatus (SCBA) on firefighters' postural stability. METHODS: Sixteen firefighters were assessed using a portable forceplate system at the fire station. Postural sway parameters were recorded at the beginning of the work shift and repeated until the work shift ended. RESULTS: Task had the greatest impact on postural stability for all sway parameters. Turnout gear, with and without SCBA, improved postural stability. Postural stability decreased as firefighters spent more time on duty. CONCLUSIONS: Prolonged work shifts may be an important contributor to the high prevalence of slips and falls among firefighters. In all, the results indicate that many aspects of the firefighters' job may adversely impact their postural stability and potentially increase the risk of falling.

Adult↗

PubMed2005

Functional impairment as a predictor of spine loading.

STUDY DESIGN: Spine loadings during a variety of lifting exertions were compared with individual torso kinematic abilities. Relationships were evaluated between these measures. OBJECTIVE: To determine if trunk kinematic status (functional impairment) is indicative of spine loading increases in patients with low back pain (LBP) compared to asymptomatic individuals. SUMMARY OF BACKGROUND DATA: Recurrent LBP is a common and costly problem that may be related to increased spine loads in those individuals with LBP. Previous studies suggest that patients with LBP had greater loading than their asymptomatic counterparts when performing work. However, we know little about how to identify when a patient with LBP can resume lifting tasks without having exaggerated spine loading. METHODS: Sixty-two patients with LBP and 61 who were asymptomatic were evaluated for signs of kinematic compromise (i.e., inability to generate normal trunk kinematic patterns) during a prelift test. All subjects were then asked to perform a variety of lifting exertions that varied in lift origin (region), lift asymmetry position, and weight lifted. An electromyography-assisted model was used to evaluate spine loading in each subject during the lifting exertions. Statistical models were used to assess the relationship between kinematic compromise and spine loading. RESULTS: Patients with LBP had greater spine loading as well as greater kinematic compromise. The degree of kinematic compromise was related to the degree of spine loading increases in those individuals with LBP. A statistical model was developed that was able to describe 87% of the variability in compression, 61% in anteroposterior shear, and 65% in lateral shear. CONCLUSIONS: Those patients with greater kinematic compromise used higher levels of antagonistic muscle coactivation that not only reduced trunk motion but also resulted in increases in spine loading. Given the degree of kinematic compromise and the lifting task conditions, a method has been devised to predict the increase in spine loading above and beyond that of an asymptomatic individual when performing typical materials handling tasks.

Biomechanical Phenomena↗

PubMed2005

Injury-induced kinematic compensations within the lower back: impact of non-lower back injuries.

With the number of musculoskeletal disorders increasing in the workplace, the potential exists for multiple injuries due to compensations. The objective of this study was to quantify the impact of non-lower back injuries on the trunk motions adopted by the individual during typical lifting tasks. A total of 32 injured subjects (eight for each injury group--shoulder, hand/wrist, knee and foot/ankle) and 32 matched (gender, height and weight) healthy subjects performed laboratory lifting tasks. The independent variables were task asymmetry (clockwise, sagittally symmetric and counter-clockwise), lift origin (waist, knee and floor) and box weight (2.27 and 6.82 kg). The dependent variables were peak trunk kinematics (as measured by the lumbar motion monitor) and moment arm between the box and lower back. The two injuries that had the greatest impact on the lower back kinematics were foot/ankle and hand/wrist. Individuals who suffered a foot/ankle injury produced greater three-dimensional trunk velocities (up to 10 degrees/s) while individuals with hand/wrist injuries slowed down in the sagittal plane but increased the twisting velocity--specifically when lifting from the asymmetric shelves. Knee and shoulder injuries had limited impact on the trunk motions. Overall, the results indicate workplace design must take into account non-lower back injuries.

Adaptation, Physiological↗

PubMed2005

Preliminary evidence of the short-term effectiveness of alternative treatments for low back pain.

In recent years, there has been increased popularity for use of alternative treatment modalities for low back pain with limited investigation into whether they are effective in returning the worker to normal functionality. The objective of this study was to investigate the short-term impact on the restoration of the functional ability of common treatment modalities including physical therapy, acupuncture, chiropractic treatment, and massage therapy. A within subjects design was used that compared a baseline assessment to three follow-up assessments: immediately following treatment, two days and seven days post treatment. Individuals suffering from low back pain were recruited from local clinics that specialize in one of the four treatment modalities. Twenty-four individuals who were suffering from low back pain and had started one of the treatment modalities were recruited into the study. Three-dimensional motions (ROM, velocity, and acceleration) during a standardized functional capacity protocol were measured prior to and during three follow-up periods. The results show the effectiveness of the treatments was dependent upon time and were predominantly in the non-sagittal motion planes (velocities and accelerations). Individual subjective pain levels also indicate all the treatment modalities were effective after the 1-week follow-up. Findings suggest those modalities primarily focused on the back musculature (acupuncture, massage, physical therapy) were more effective with respect to functional capacity restoration. The current results provide a quantitative evaluation, based upon trunk dynamics, of the effectiveness of these four treatment modalities.

Adult↗

PubMed2004

Differences in motor recruitment and resulting kinematics between low back pain patients and asymptomatic participants during lifting exertions.

BACKGROUND: Low back disorders are a prevalent problem in society today and may lead to chronic debilitating low back pain. Developing our understanding of temporal muscle and kinematic patterns during manual material handling tasks may provide insight for preventing the cascading series of events leading to chronic low back pain. METHODS: Sixty-two low back pain patients and 61 asymptomatic participants performed a variety of lifting exertions that varied in lift origin horizontal and vertical distance, lift asymmetry, and weight. Electromyographic activity of 10 trunk muscles as well as trunk and pelvic kinematics was recorded during each exertion. Differences in muscle activation and kinematic parameters were compared between low back pain patients and asymptomatic participants as a function of experimental conditions. FINDINGS: Both the left and right erector spinae activated significantly earlier and were on significantly longer in low back pain patients compared to asymptomatic participants. The horizontal and vertical location of the lift influenced the EMG and kinematic differences between the low back pain patients and asymptomatic participants. INTERPRETATION: These finding indicate that low back pain patients would be exposed to increase muscle activity resulting in higher spine loads for a greater length of time compared to asymptomatic participants. The longer exposure time to increased spine load may lead to greater risk of future low back injury and cascading events leading to debilitating low back pain. The longer muscle activation time suggests that low back pain patients have changed their motor program from an open to a closed loop system.

Adult↗

PubMed2002

The impact of mental processing and pacing on spine loading: 2002 Volvo Award in biomechanics.

STUDY DESIGN: The impact of various levels of mental processing and pacing (during lifting) on spine loading was monitored under laboratory conditions. OBJECTIVES: To explore how mental demands and pacing influence the biomechanical response and subsequent spine loading and, to determine whether individual characteristics have a modifying role in the responses. SUMMARY OF BACKGROUND DATA: Modern work often requires rapid physical exertions along with demands of mental processing (both psychosocial stressors). While the effect of physical workplace factors on spine loading has been widely documented, few studies have investigated the impact that interaction of psychosocial factors and individual factors has on spine loads. METHODS: For this study, 60 subjects lifted boxes while completing two types of mental processing tasks: 1) series tasks with decisions occurring before the act of lifting, and 2) simultaneous tasks with decisions occurring concurrently with the lift. For both of these mental processing conditions, two intensities of mental load were evaluated: simple and complex. Task pacing was also adjusted under slow and fast conditions. Finally, individual characteristics (personality and gender) were evaluated as potential modifiers. An electromyographically assisted model evaluated the three-dimensional spine loads under the experimental conditions. RESULTS: Simultaneous mental processing had the largest impact on the spine loads, with the complex intensity resulting in increases of 160 N with lateral shear, 80 N with anteroposterior shear, and 700 N with compression. Increased task pace produced greater lateral shear (by 20 N), anteroposterior shear (by 60 N), and compression loads (by 410 N). Gender and personality also influenced loadings by as much as 17%. CONCLUSIONS: Mental processing stress acted as a catalyst for the biomechanical responses, leading to intensified spine loading. Mental stress appeared to occur as a function of time pressures on task performance and resulted in less controlled movements and increases in trunk muscle coactivation. These adjustments significantly increased spine loading. These results suggest a potential mechanism for the increase in low back pain risk resulting from psychosocial stress caused by modern work demands.

Adult↗

PubMed2002

Spine loading as a function of gender.

STUDY DESIGN: In vivo laboratory studies were conducted to investigate the spine loads imposed on men and women during a series of lifting tasks that varied in the degree of lifting control required by the subject. OBJECTIVE: To identify and understand differences in spine loading and musculoskeletal control strategies between men and women performing lifts of varying task complexity. SUMMARY OF BACKGROUND DATA: Few studies have examined differences in spine loading as a function of individual factors such as subject gender. Furthermore, no biomechanical studies have attempted to quantify and understand how differences in anthropometry between genders might influence muscle recruitment and subsequent spine loads. Because the modern workplace seldom discriminates between genders in job assignments, it is important to understand how differences in spine loading and potential low back disorder risk might be associated with gender differences. METHODS: For this study, 140 subjects participated in two separate experiments requiring different degrees of musculoskeletal motion control during sagittal plane lifting. The two experiments consisted of 35 men and 35 women performing lifts in which motion was isolated to the torso and 35 men and 35 women completing whole-body free-dynamic whole body lifts. An electromyography-assisted model was used to evaluate spine loading under these conditions. RESULTS: Absolute spine compression generally was greater for the men. Under the highly controlled (isolated torso) conditions, most differences were attributed solely to differences in body mass. Under a whole-body free-dynamic condition, significant differences in muscle coactivations resulted in greater relative compression and anterior-posterior shear spine loading for the women. CONCLUSIONS: Differences in spine loadings as a function of gender under the more controlled lifting conditions were primarily a function of different body masses. However, loading pattern differences existed between the genders under whole-body free-dynamic conditions as a result of kinematic compensations and increases in muscle cocontraction, with women generally experiencing greater relative loads. When spine tolerance differences are considered, one would expect that females would be at greater risk of musculoskeletal overload during lifting tasks.

Abdomen↗

PubMed2002

Effects of posture on dynamic back loading during a cable lifting task.

This study evaluated spinal loads associated with lifting and hanging heavy mining cable in a variety of postures. This electrical cable can weigh up to 10 kg per metre and is often lifted in restricted spaces in underground coal mines. Seven male subjects performed eight cable lifting and hanging tasks, while trunk kinematic data and trunk muscle electromyograms (EMGs) were obtained. The eight tasks were combinations of four postures (standing, stooping, kneeling on one knee, or kneeling on both knees) and two levels of cable load (0 N or 100 N load added to the existing cable weight). An EMG-assisted model was used to calculate forces and moments acting on the lumbar spine. A two-way split-plot ANOVA showed that increased load (p < 0.05) and changes in lifting posture (p < 0.05) independently affected trunk muscle recruitment and spinal loading. The increase in cable load resulted in higher EMG activity of all trunk muscles and increased axial and lateral bending moments on the spine (p < 0.05). Changes in posture caused more selective adjustments in muscle recruitment and affected the sagittal plane moment (p < 0.05). Despite the more selective nature of trunk EMG changes due to posture, the magnitude of changes in spinal loading was often quite dramatic. However, average compression values exceeded 3400 N for all cable lifting tasks.

Adult↗

PubMed1998

Evaluation of spinal loading during lowering and lifting.

OBJECTIVE: To estimate the three-dimensional spinal loads during various lifting and lowering tasks. DESIGN: The in vivo measurements of the trunk dynamics, moments, and myoelectric activity were used as inputs into an electromyographic-assisted model used to predict the three-dimensional spinal loads. BACKGROUND: Previous studies of eccentric motions have investigated muscle activity, trunk strength, and trunk moments. A void in the body of knowledge exists in that none of these studies investigated spinal loading. METHODS: Ten subjects lifted (40 degrees of flexion to 0 degrees ) and lowered (0 degrees of flexion to 40 degrees ) boxes while positioned in a structure that restrained the pelvis and hips. The tasks were performed under isokinetic trunk velocities of 5, 10, 20, 40, and 80 deg s(-1) while holding a box with weights of 9.1, 18.2, and 27.3 kg. RESULTS: Lowering strength was found to be 56% greater than lifting strength. The lowering tasks produced significantly higher compression forces but lower anterior-posterior shear forces than the lifting tasks. The differences in the spinal loads produced by the two lifting tasks were attributed to differences in coactivity and unequal lifting moments (i.e. holding the box farther away from the body). CONCLUSIONS: The nature of the spinal loads that occur during lowering and lifting were significantly different. The difference in spinal loads may be explained by different lifting styles.

Journal Article↗

PubMedDate not supplied

Gender influences on spine loads during complex lifting.

BACKGROUND CONTEXT: Previous research has documented differences in spine loading between genders when the imposed load is normalized relative to the size of the person. However, under realistic work conditions the magnitude of the load handled is seldom adjusted relative to worker anthropometry. Thus, there is a void in our knowledge in that we do not understand how material handling influences spine loading and potential risk of injury as a function of gender under realistic lifting situations. PURPOSE: To evaluate the differences in spine loading between men and women when exposed to similar workplace demands. STUDY DESIGN: A laboratory study was conducted to investigate the biomechanical responses during realistic free-dynamic lifting tasks when subjects lifted from origins and destinations that were either fixed or set relative to the subject's anthropometry. PATIENT SAMPLE: Twenty men and 20 women asymptomatic for low back pain were recruited to participate in the study. OUTCOME MEASURES: The three-dimensional spine loads were predicted from a well-established electromyography-assisted model. METHODS: Both genders completed a series of symmetric and asymmetric (60-degree clockwise) lifts that originated from two shelf heights ("relative" to knee height and "set" at 35 cm from floor) and terminated at one of two destination heights ("relative" to waist and "set" 102 cm from the floor). Three levels of box weight were investigated (6.8, 13.6 and 22.7 kg). RESULTS: Men had significantly greater compression forces than women (about 640 N). Loading differences between genders were further magnified by several of the workplace factors. The differences between men and women were even greater when lifting either of the heavier loads from the lower fixed shelf (more than 50% greater). CONCLUSIONS: It is apparent that men produce the greater loads on their spines during lifting. However, engineering controls, such as adjustable workplace layout or less weight lifted, may reduce or eliminate gender-specific differences in spine loads. Furthermore, the differences in spine loads appear to be a result of kinematic trade-offs and muscle coactivity differences in combination with unequal body masses between genders. However, when the loads were put into context of the expected tolerances of the spine, women were found to be at increased risk of injury, especially when lifting heavy loads or under asymmetric lifting conditions. Collectively, the results indicate the need to account for differences between the genders when designing the workplace.

Adult↗

PubMedDate not supplied

Partitioning the contributing role of biomechanical, psychosocial, and individual risk factors in the development of spine loads.

BACKGROUND CONTEXT: The role of biomechanical workplace factors in spine loading has been well documented. However, our understanding of the role of psychosocial and individual factors in producing spine loads is poorly understood. Even less is understood about the relative contribution of these factors with respect to kinematic, kinetic and muscle activity responses, as well as spine loading. PURPOSE: To explore the relative contribution of biomechanical and psychosocial workplace factors and individual characteristics on the biomechanical responses and spine loading. STUDY DESIGN/SETTING: The contribution of various levels of workplace factors to spine loading was monitored under laboratory conditions. PATIENT SAMPLE: Sixty (30 male and 30 female) college-age individuals who were asymptomatic to low back pain. OUTCOME MEASURES: Trunk kinematics and kinetics, muscle activity and the three-dimensional spinal loads. METHODS: The subjects performed lifting tasks while being exposed to varying levels of biomechanical (lift rate, load weight and task asymmetry) and psychosocial (social support and mental concentration) workplace factors as well as an unexplored (load placement) workplace factor. RESULTS: The workplace job demands that had the largest contribution were load placement (4% to 30%) and load weight (15% to 55%). Mental concentration and social environment had a relatively small contribution to the spinal loads (up to 0.2%). Anthropometry played a large role in the shears (about 12% to 58%) but a relatively minor role in the compressive forces (about 3%). CONCLUSIONS: Under the given experimental conditions, load weight is the most important factor when controlling compression forces associated with lifting, but other factors, such as individual characteristics, significantly contribute to the shear loads. Thus, one must account for the weight lifted and the anthropometric dimensions when designing the workplace. For the first time, the relative contribution of workplace job demands and individual factors in the development of spine loading have been identified.

Adult↗

PubMedDate not supplied

Spine loading in patients with low back pain during asymmetric lifting exertions.

BACKGROUND CONTEXT: Recurrent low back pain (LBP) is a common and costly problem that might be related to increased spine loads in those with LBP. However, we know little about how the spine is loaded when those with LBP perform lifting exertions. PURPOSE: Document spine loading patterns of patients with LBP performing symmetric and asymmetric lifting exertions compared with asymptomatic individuals performing the same tasks. STUDY DESIGN: Spine loadings during lifting exertions that varied in asymmetric origin as well as horizontal and vertical distance from the spine were compared between asymptomatic subjects and patients with LBP. METHODS: Sixty-two patients with LBP and 61 asymptomatic individuals performed a variety of lifting exertions that varied in lift origin horizontal and vertical position (region), lift asymmetry position and weight lifted. An electromyography-assisted model was used to evaluate spine loading in each subject during the lifting exertions. Differences in spine loading between the LBP and asymptomatic subjects were noted as a function of the experimental variables. RESULTS: Patients with LBP experienced greater spine compression and shear forces when performing lifting tasks compared with asymptomatic individuals. The least taxing conditions resulted in some of the greatest differences between LBP and asymptomatic individuals. CONCLUSIONS: Greater levels of antagonistic muscle coactivation resulted in increases in spine loading for patients with LBP. Specific lifting conditions that tend to exacerbate loading can be identified by means of physical workplace requirements. These findings may impact acceptable return-to-work conditions for those with LBP.

Adult↗