Maximal step-up height as a novel assessment of leg muscle strength and function : methodological and clinical studies

Sammanfattning: Physical performance is a strong predictor for morbidity and premature death and there is an increasing interest in the role of sarcopenia in many chronic diseases. There is a need for simple, robust and valid tests for assessing muscle strength and function in clinical practice. A novel maximal step-up test (MST) was developed and standardised to fulfil this need. The aims of this thesis were to study the repeatability and validity of MST (Study I) and to study the associations to age, anthropometric variables, maximal oxygen uptake (VO2 max) and self-reported physical function before and after a 3-month group training intervention programme (Study II). Furthermore, the aim was to study the long-term effects of the intervention programme on maximal step-up height (MSH) after an average of 22 months (Study III). In Study I, MSH was tested with MST on middle-aged women and men (30/30) with capacity to work. 178 female patients were recruited from primary health care for Study II, all of whom had joint and muscular problems and most of whom also had reduced capacity to work, metabolic risk factors and other chronic diseases. For Study III, 101 out of these female patients were recruited. They participated in a 3-month group training intervention programme, which included three sessions per week of mixed aerobic fitness and strength training. The repeatability of MSH between test occasions and between testers was 6 cm in Study I and 4 cm between testers at 22-month follow-up in Study III. In Study I, MSH was significantly correlated to isokinetic knee extension peak torque (r=0.68, p<0.001), self-reported physical function (r=0.29, p=0.03) as well as sex, age, weight and body mass index (BMI). MSH above 32 cm discriminated subjects with no limitation in self-reported physical function. In Study II, at baseline and after the 3-month intervention MSH was negatively correlated to age, body weight and waist circumference and positively correlated to self-reported physical function, VO2 max and height. MSH correlated to training intensity at follow-up. Changes in MSH were significantly correlated to changes in waist circumference and physical function regardless of age and changes in VO2 max. MSH below 24 cm discriminated female patients with self-reported severe limitation in physical function. The long-term investigation in Study III showed that MSH increased significantly from 27.2 (5.7) cm at baseline to 29.0 (5.5) cm after three months and thereafter decreased to 25.2 (5.5) cm at the long-term follow-up. Time to follow-up (B=-0.42, p<0.001) and change in BMI (B=-0.29, p=0.012) correlated significantly to changes in MSH. Waist circumference, VO2 max, physical function and exercise/physical activity levels were significantly improved at long-term follow-up, while BMI did not change. In a univariate logistic regression model, maintenance of MSH correlated to the extent of mixed training (OR 3.33, 95% CI 1.25-8.89). In a multivariate logistic regression model adjusted for important factors, the correlation was not significant. However, MSH was significantly higher in individuals participating in 2-3 sessions of exercise per week compared to one session. In conclusion, the novel maximal step-up test assessing maximal step-up height is considered to be a useful and reliable test for leg function in clinical practice. It may also function as an indicator of metabolic health. The results of a 3-month group training intervention programme with 2-3 sessions per week of mixed aerobic fitness and strength training demonstrated increasing maximal step-up height, improved fitness and decreased risk in female patients with elevated cardio-metabolic risk. After an average of 22 months without regular group training, maximal step-up height was reduced again, while positive effects remained for waist circumference, VO2 max, physical function and physical activity. However, regular group exercise 2-3 times per week with mixed aerobic fitness and strength training was associated with maintenance of maximal step-up height in a subgroup of women. Brisk walking for at least 150 minutes per week was not sufficient to maintain maximal step-up height in a subgroup of women.