Biomedical subjects

Tine Alkjaer

Publications and source records attributed to Tine Alkjaer.

8 recordsLinked to original sources

PubMed2006

Biomechanical analysis of rollator walking.

BACKGROUND: The rollator is a very popular walking aid. However, knowledge about how a rollator affects the walking patterns is limited. Thus, the purpose of the study was to investigate the biomechanical effects of walking with and without a rollator on the walking pattern in healthy subjects. METHODS: The walking pattern during walking with and without rollator was analyzed using a three-dimensional inverse dynamics method. Sagittal joint dynamics and kinematics of the ankle, knee and hip were calculated. In addition, hip joint dynamics and kinematics in the frontal plane were calculated. Seven healthy women participated in the study. RESULTS: The hip was more flexed while the knee and ankle joints were less flexed/dorsiflexed during rollator walking. The ROM of the ankle and knee joints was reduced during rollator-walking. Rollator-walking caused a reduction in the knee extensor moment by 50% when compared to normal walking. The ankle plantarflexor and hip abductor moments were smaller when walking with a rollator. In contrast, the angular impulse of the hip extensors was significantly increased during rollator-walking. CONCLUSION: Walking with a rollator unloaded the ankle and especially the knee extensors, increased the hip flexion and thus the contribution of hip extensors to produce movement. Thus, rollator walking did not result in an overall unloading of the muscles and joints of the lower extremities. However, the long-term effect of rollator walking is unknown and further investigation in this field is needed.

Adult↗

PubMed2005

Exercise-induced rib stress fractures: influence of reduced bone mineral density.

Exercise-induced rib stress fractures have been reported frequently in elite rowers during the past decade. The etiology of rib stress fractures is unclear, but low bone mineral density (BMD) has been suggested to be a potential risk factor for stress fractures in weight-bearing bones. The present study investigated BMD in seven Danish national team rowers with previous rib stress fracture (RSF) and 7 controls (C) matched for gender, age, height, weight and training experience. Total body scan and specific scans of the lumbar spine (L2-L4), femoral neck and distal radius were performed using a DEXA scanner. The RSF subjects showed significantly lower L2-L4 BMD: RSF: 1.22+/-0.05 g cm(-2) (mean+/-SEM) (median 1.19 g cm(-2), range 1.02-1.37 g cm(-2)) compared to C: 140+/-0.04 g cm(-2) (median 1.41 g cm(-2), range 1.27-1.57 g cm(-2)) (P=0.028). The present results suggest that low bone mineral density may be a potential risk factor for the development of exercise-induced rib stress fractures in elite rowers.

Absorptiometry, Photon↗

PubMed2005

Effect of aging on performance, muscle activation and perceived stress during mentally demanding computer tasks.

OBJECTIVES: This study examined the effects of age on performance, muscle activation, and perceived stress during computer tasks with different levels of mental demand. METHODS: Fifteen young and thirteen elderly women performed two computer tasks [color word test and reference task] with different levels of mental demand but similar physical demands. The performance (clicking frequency, percentage of correct answers, and response time for correct answers) and electromyography from the forearm, shoulder, and neck muscles were recorded. Visual analogue scales were used to measure the participants' perception of the stress and difficulty related to the tasks. RESULTS: Performance decreased significantly in both groups during the color word test in comparison with performance on the reference task. However, the performance reduction was more pronounced in the elderly group than in the young group. Likewise, a higher level of self-reported stress was found for the elderly participants after the color word test. During the reference task higher electromyographic levels and reported difficulty were recorded for the elderly group than for the young group. CONCLUSIONS: The findings suggest that mental demands affect young and elderly women differently. Thus the mentally demanding computer task had a more pronounced effect on the elderly than on the young. In contrast to the results in the reference task, the same level of muscle activity for most muscles and the same level of self-reported difficulty was found in the two groups during the color word test. The elderly probably compensated for age-related changes by reducing their work speed markedly.

Adaptation, Physiological↗

PubMed2004

Walking pattern in adults with congenital hip dysplasia: 14 women examined by inverse dynamics.

BACKGROUND: Knowledge of the gait dynamics in patients with hip dysplasia may help to understand the consequences of the mechanical changes in the hip. PATIENTS AND METHODS: We evaluated the walking pattern of 14 women with hip dysplasia (median age 39 (24-50) years) before periacetabular osteotomy and compared it with a control group of 12 healthy women (median age 35 (24-56) years). Data were collected using five video cameras and two force plates. We used an inverse dynamics approach to calculate sagittal joint angles, moments and power in the stance phase. RESULTS: The patient group showed increased dorsiflexion of the ankle and knee flexion in the second half of the stance phase. The hip flexor joint moment in the patient group was both delayed and reduced in the second half of the stance phase. Moreover, the angular impulse of the hip flexors was significantly reduced in the patient group. INTERPRETATION: The pathological deformities of hip dysplasia may explain both the kinematic and kinetic gait deviations between the patient group and the control group in the second half of the stance phase. We suggest that insufficient cover of the femoral head leads to a reduced hip flexor moment and an increased flexion in the ankle, knee and hip joints.

Adult↗

PubMed2003

Evaluation of the walking pattern in two types of patients with anterior cruciate ligament deficiency: copers and non-copers.

The purpose of the present study was to investigate whether different walking patterns in healthy subjects and in coper and non-coper subjects with deficient anterior cruciate ligaments could be quantified. An inverse dynamics approach was used to calculate joint kinematics and kinetics for flexion and extension. EMG signals of the hamstrings and quadriceps muscles were recorded. The results showed that the peak knee flexion angle was greater in the copers than in the controls. There was a positive correlation between the peak knee extensor moment and peak knee flexion angle. Furthermore, at a given peak knee flexion angle, the peak knee extensor moment was significantly larger in the controls than in the non-copers. The hip extensor moment in the copers was significantly larger than that of the non-copers and the controls. In conclusion, the three groups walked according to different patterns. It is suggested that the copers stabilized their knee joint by co-contraction of the hamstrings and quadriceps muscles, while the non-copers lacked this ability. Instead, the non-copers reduced the knee extensor moment in order to decrease anterior displacement of the tibia. The walking pattern differences observed between the copers and non-copers may explain their different post-injury activity levels.

Adaptation, Physiological↗

PubMed2002

Differences in the movement pattern of a forward lunge in two types of anterior cruciate ligament deficient patients: copers and non-copers.

OBJECTIVE: To determine whether differences in the knee joint movement pattern of a forward lunge could be quantified in healthy subjects and in anterior cruciate ligament deficient subjects who were able to return to the same activity level as before their injury (copers) and in those who were not (non-copers). DESIGN: The movement patterns of the injured leg of the coper and non-coper anterior cruciate ligament deficient subjects and the right leg of the control subjects were compared statistically. BACKGROUND: The forward lunge seems to be a less stressful test than the commonly used one-legged hop test, which makes it a possible tool for evaluating and comparing the functional performance of non-copers and copers. METHODS: The movement pattern of a forward lunge was analysed by using a two-dimensional inverse dynamics method. The electromyographic activity of the quadriceps and hamstring muscles were recorded. RESULTS: The non-copers moved more slowly and loaded the knee joint less than the copers and controls. The copers moved more slowly during the knee flexion phase but as fast as the controls during the knee extension. The EMG results suggest that the copers stabilized their knee joint by increasing the co-contraction of the hamstrings during the extension phase. CONCLUSIONS: Differences between the three groups' movement patterns could be quantified. The forward lunge test seems appropriate to discriminate between the knee function in coper and non-coper anterior cruciate ligament deficient subjects. RELEVANCE: Information about the performance of movements, which significantly load the knee joint in coper and non-coper anterior cruciate ligament deficient patients may contribute to a better understanding of dynamic knee joint stabilization, which is relevant in relation to the development of rehabilitation strategies.

Adaptation, Physiological↗

PubMed2001

Interindividual differences in H reflex modulation during normal walking.

Based on previous studies, at least two different types of soleus Hoffmann (H) reflex modulation were likely to be found during normal human walking. Accordingly, the aim of the present study was to identify different patterns of modulation of the soleus H reflex and to examine whether or not subjects with different H reflex modulation would exhibit different walking mechanics and different EMG activity. Fifteen subjects walked across two force platforms at 4.5 km/h (+/-10%) while the movements were recorded on video. The soleus H reflex and EMG activity were recorded separately during treadmill walking at 4.5 km/h. Using a two-dimensional analysis joint angles, angular velocities, accelerations, linear velocities and accelerations were calculated, and net joint moments about the ankle, knee and hip joint were computed by inverse dynamics from the video and force plate data. Six subjects (group S) showed a suppressed H reflex during the swing phase, and 9 subjects (group LS) showed increasing reflex excitability during the swing phase. The plantar flexor dominated moment about the ankle joint was greater for group LS. In contrast, the extensor dominated moment about the knee joint was greater for the S group. The hip joint moment was similar for the groups. The EMG activity in the vastus lateralis and anterior tibial muscles was greater prior to heel strike for the S group. These data indicate that human walking exhibits at least two different motor patterns as evaluated by gating of afferent input to the spinal cord, by EMG activity and by walking mechanics. Increasing H reflex excitability during the swing phase appears to protect the subject against unexpected perturbations around heel strike by a facilitated stretch reflex in the triceps surae muscle. Alternatively, in subjects with a suppressed H reflex in the swing phase the knee joint extensors seem to form the primary protection around heel strike.

Adult↗

PubMedDate not supplied

Salivary cortisol level, salivary flow rate, and masticatory muscle activity in response to acute mental stress: a comparison between aged and young women.

BACKGROUND: Age-related effects on physiological stress reactions regarding changes in salivary cortisol concentration, saliva flow rate, and masticatory muscle activity, as well as the corresponding perceived mental stress and performance in response to acute stressors, have not yet been fully described. OBJECTIVE: Thus, the aim of this study was to assess the age-related variations in these variables in response to minor acute and naturalistic stressors in terms of computer tasks. METHODS: 13 aged (60-70 years old) and 13 young (20-30 years old) women with frequent practice and long experience with computer use were recruited by personal contact and flyers. The subjects were healthy and had full dental arches and no orofacial pain. The computer tasks were randomized and comprised a mentally demanding, modified Stroop colour-word test (CWT) and a less demanding reference test, both with a duration of 20 min and with equal physical demand. Visual analogue scales for global assessment of mental stress and perceived task difficulty and performance, measurements of saliva flow rate and cortisol concentration (unstimulated whole saliva), as well as surface electromyography of the temporalis and masseter muscles were used for assessment, and Spearman correlation analysis and Anova with repeated measures were used for statistical evaluation. RESULTS: The perceived task-related stress and task difficulty were significantly higher and the personal satisfaction with the task performance significantly poorer in the aged women. The cortisol concentration, indicating the stress level, showed a small, but significant increase in response to the tasks. Also the saliva flow rate increased. This response was most pronounced in the aged and during the CWT. The average electromyogram varied significantly between age groups and tasks, with higher levels and shorter relative periods with gaps in the aged women and in the CWT. In addition, the peak activity of the jaw elevator muscles at mouse clicking was significantly elevated as a form of co-activation or attention-related activity. CONCLUSIONS: The study showed marked differences in the response to mental demands in aged as compared with young women. The mental stress, reflected by increases of salivary cortisol concentration, saliva flow rate, visual analogue scale ratings, and activity level of the jaw elevator muscles, was more pronounced in the aged women in response to the computer tasks.

Adult↗