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Muscle strength assessment from functional performance tests: role of body size
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences.
2003 (English)In: Journal of Strength and Conditioning Research, ISSN 1064-8011, Vol. 17, no 4, 664-670 p.Article in journal (Refereed) Published
Abstract [en]

The aim of the study was to test the hypothesis that the body size plays an important role in assessment of muscle ability to exert force by standard functional performance tests. Twenty-one male students were tested on maximal isometric lift, one leg rising, vertical jump, and box lift tests, and the maximal isokinetic strength of hip and knee extensors was also recorded. When indices of the 4 functional performance tests were related to the strength of each of the 2 leg extensor muscle groups, only maximal isometric lift demonstrated positive correlation with knee extensors strength. When muscle strength was corrected for body mass, however, the aforementioned relationship became insignificant, but the 1 leg rising performance demonstrated a positive relationship with knee extensor strength. In addition, maximal isometric lift and 1 leg rising test performance provided positive and negative correlation, respectively, with body mass. The obtained findings were in line with the effects of scale applied on the tested performance. We generally conclude that the assessment of muscle capability to exert force based on some standard functional performance tests could be confounded by the body size effect.

Place, publisher, year, edition, pages
2003. Vol. 17, no 4, 664-670 p.
Keyword [en]
effects of scale, isokinetic force, movement task, body mass
URN: urn:nbn:se:umu:diva-4436PubMedID: 14636094OAI: diva2:143544
Available from: 2005-03-17 Created: 2005-03-17 Last updated: 2010-11-19Bibliographically approved
In thesis
1. Ambulance Work: Relationships between occupational demands, individual characteristics and health-related outcomes
Open this publication in new window or tab >>Ambulance Work: Relationships between occupational demands, individual characteristics and health-related outcomes
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Although musculoskeletal disorders (MSDs) and other health complaints are an occupational problem for ambulance personnel, there is a lack of knowledge regarding work-related factors associated with MSDs and other health complaints. The overall aim of this thesis was to investigate the relationships between occupational demands, individual characteristics and health-related outcomes among ambulance personnel.

A random sample of 234 female and 953 male ambulance personnel participated in a national questionnaire survey on work-related factors, and musculoskeletal and other health complaints. Physical demands was associated with activity limitation due to neck-shoulder and low-back complaints among the female personnel. Among the male personnel, physical demands was associated with low-back complaints and activity limitation due to low-back complaints. Psychological demands was significantly associated with neck-shoulder complaints, sleeping problems, headache and stomach symptoms among both female and male ambulance personnel. Worry about work conditions was associated with musculoskeletal disorders and sleeping problems, headache and stomach symptoms.

A local sample of 26 ambulance personnel was followed during a 24-hour work shift and for the next two work-free days. Subjective stress- and energy levels, and cortisol levels were measured at regular intervals, and heart rate was registered continuously by electrocardiogram (ECG). Autonomic reactivity to standardized tests before (pre-work) and at the end of the work shift (post-work) was also investigated. For the whole group, baseline values of heart rate were higher pre-work than post-work, but autonomic reactivity did not differ. Increased reactivity to the mental test, modest deviation in heart rate variability (HRV) pattern during the late night hours at work and higher morning cortisol values during work than during leisure time were observed in personnel with many health complaints, but not among their co-workers without or with few complaints. Ambulance personnel with many health complaints also reported higher psychological demands and tended to be more worried about work conditions.

Heart rate (HR), lactate level (LL) and perceived exertion (RPE) were investigated in 17 female and 48 male ambulance personnel during a simulated standardized work task “carry a loaded stretcher”. The ambulance personnel had to carry the loaded stretcher (920 N) up and down three flights of stairs twice. The high physiological strain (HR, LL, RPE) for the male, and near or at maximal strain for the female ambulance personnel, implied the importance to identify what kind of physical capacity is most important for ambulance personnel. Therefore, the explained variance of developed fatigue by tests of cardiorespiratory capacity, muscular strength and endurance, and coordination was investigated. The results showed that VO2max and isometric back endurance were important predictors for development of fatigue when carrying a loaded stretcher.

The influence of body size on the relationships between maximal strength and functional performance was investigated in a methodological study. The results confirm that the assessment of physical performance could be confounded by the body weight. Therefore, the models for explaining development of fatigue when carrying the loaded stretcher were adjusted for height and weight. Including height in the models significantly increased the explained variance of accumulated lactate among female, but not among male personnel. Lactate levels were higher among short compared to tall female personnel. Weight had no effect on any of the models.

In conclusion, the national survey showed that self-reported physical demands was a risk factor of having MSDs, and that self-reported psychological demands and worry about work were important risk factors of having MSDs and other health complaints. Stress monitoring of ambulance personnel during work and leisure time showed that physiological and subjective stress markers did not show any differences between the 24-hour ambulance work shift and leisure time afterwards. However, ambulance personnel with many health complaints had certain physiological changes during the work shift in comparison with the next two work-free days. The physiological and subjective responses during carrying a loaded stretcher, especially among the female ambulance personnel, showed that female and male ambulance personnel could be exposed to internal exposures at different levels when performing the same work task. A better understanding of the relationships between occupational demands and health-related outcomes require further studies on age- and gender matched groups in long-term perspective studies.

75 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 943
ambulance, autonomic reactivity, body size, cortisol, demand-control-support, emergency personnel, fitness, gender, heart rate variability, low-back pain, neck-shoulder pain, occupational, physical capacity, work simulated test, worry
Research subject
Occupational and Environmental Medicine
urn:nbn:se:umu:diva-478 (URN)91-7305-820-3 (ISBN)
Public defence
2005-04-08, Stora föreläsningssalen, Arbetslivsinstitutet, Umeå, 09:00 (English)
Available from: 2005-03-17 Created: 2005-03-17 Last updated: 2010-02-19Bibliographically approved

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Aasa, Ulrika
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