Screening and treating pre-sarcopenia in middle-aged adults

Despite the presence of pre-sarcopenia (stage of sarcopenia in which muscle mass deteriorates, but muscle strength is still intact) in middle-aged adults, previous research has focussed on older individuals. A better understanding of early markers of sarcopenia, age-appropriate screening models, and exercise focused prevention-based interventions, will assist to counteract the surging prevalence of sarcopenia in the ageing population. The first part of this thesis used the Dunedin Multidisciplinary Health and Development Study data (n = 899) to classify pre-sarcopenic participants based on appendicular lean soft tissue mass index (ALMI) and grip strength. The relationship between pre-sarcopenia at age 45, and pro-dromal markers at ages 26, 32 and 38, was assessed by multivariate logistic regression. Regression models were internally validated, and overall performance, calibration and discrimination of the models were estimated. These models were confirmed using logistic least absolute selection and shrinkage operator regression. Furthermore, female age 38 models were externally validated in a separate sample of adults (n = 99). The second part of this thesis consisted of a 40-week, single-blinded, randomised controlled trial (RCT), conducted in eighty-two middle-aged adults with low ALMI. Participants were randomly allocated to group-based, 20-week high intensity aerobic and resistance training (HIART) (n = 41), or a single education session (n = 41). The initial 20-weeks were followed by a 20-week HIART home program for both groups. Outcome measures included body composition, physical function, and physical fitness. The primary outcome measure, lean soft tissue mass, was assessed at baseline, 20-weeks, and 40-weeks. Analyses were performed using intention to treat principles and linear mixed models. The first part of this thesis indicated that, in females, protective factors included high BMI from age 26 onward, and high grip strength at age 38. In males, low self-perceived fitness level at age 38 was a risk factor of pre-sarcopenia, whereas significant protective factors included a high BMI from age 26 onward and high grip strength at age 38. The sex-specific regression models revealed an explained variance that increased from age 26 to age 38 and showed good accuracy of the models. External validation in females demonstrated good discrimination and calibration, as well as a high level of sensitivity (0.92) and specificity (0.76). For the second part of this thesis, the sample for the RCT included 82 participants (mean age 45.1 years; BMI 25.8 kg/m2) of which 85% were female. Significant group differences were observed in favour of the intervention group, after 20-weeks for measures of body composition, physical function, and physical fitness. Furthermore, lean soft tissue mass and the 30-seconds sit-to-stand remained significant at 40-weeks. This thesis highlighted the association of pre-sarcopenia with modifiable markers in middle-aged adults. Screening for these markers predicted sex-specific risks of pre-sarcopenia in the targeted population, which was internally and externally validated. Furthermore, HIART was shown to be a safe, tolerable, and effective exercise intervention to mitigate the loss of lean soft tissue mass, in middle-aged adults with low ALMI