66 GRIP STRENGTH, ONLY A PHYSICAL TASK? ASSOCIATIONS BETWEEN RESTING-STATE BRAIN CONNECTIVITY AND GRIP STRENGTH

Background

Grip strength (GS) is a simple measure used in the assessment of frailty and sarcopenia. Despite being physical, studies show that it is also related with depression and cognition. Our aim was to explore if brain connectivity is implicated in GS.

Methods

Participants from Wave 3 of TILDA with adequate resting-state functional-MRI data were included. Connectome-based predictive modelling was used on Shen parcellated brain connectivity matrices to find connections that are positively and negatively associated with grip strength: positive and negative networks (PN and NN). On each iteration of a randomized 10-fold cross-validation, the training folds were utilized to perform partial Spearman correlations (age-, sex-adjusted) between each connection and GS. Significant (p<0.001) connections were selected. PN and NN strengths were computed by summing across all significant correlations. Linear models regressing GS on network strengths were built on training data and used to predict GS in the test fold. After 10 folds were complete the performance was measured via Pearson R between predicted and true GS values. This 10-fold process was repeated 1000 times and a mean R obtained. Permutation significance testing was employed where the cross-validation procedure was repeated 1000 times, with GS randomly shuffled each time. The P-value was the proportion of permuted R values >= the mean R.

Results

317 participants were included (mean(SD) age 67.3(7.2) and 49.8% female). For PN: R[95% intervals]=0.29[0.26, 0.32], P<0.001 and for NN: R=0.24[0.20, 0.28], P<0.001. In both, the default mode, dorsal attention, and cerebellum networks were highly involved but with differing patterns: most notable was the presence of high connectivity between both cerebellar hemispheres in the PN but not in the NN.

Conclusion

Grip strength is related with different brain connectivity patterns suggesting the involvement of networks beyond motor areas. Further studies are required to disentangle the neuroscience behind this clinically relevant physio-cognitive task.

81 LONGER CHAIR-STAND TIME IS ASSOCIATED WITH ORTHOSTATIC INTOLERANCE IN AN OLDER IRISH POPULATION

Background

Hospital admissions for orthostatic hypotension (OH) have risen more than two-fold in the past ten years. OH can lead to orthostatic intolerance (OI), and both OH and OI are common causes of falls and injuries in older persons. Sarcopenia is also common in older persons and associated with adverse health outcomes. The 5-chair stand test (5-CST) can be used as a marker of sarcopenia and a cut-off of 15 s has been proposed. We hypothesized that those with a worse performance on the 5-CST would be at greater risk of OH and sought to investigate this in an older Irish population cohort study.

Methods

5-CST was measured in keeping with a standardised protocol. Beat-to-beat blood pressure was measured with the Finometer device according to the active stand protocol. Multivariable logistic regressions were performed to investigate the associations between OH at 40 seconds after standing (OH40), OI (dizziness after standing), and 5-CST time. Potential confounders were controlled for in the model including age, sex, education, body mass index and medications.

Results

Data from 3,119 participants were available for analysis. Mean age was 63.8 years, 55% were female, 25% took longer than 15s on the 5-CST and mean baseline blood pressure was 141/76 mmHg. Proportion of OH40 was 12.5% and 4.4% reported OI. In the multivariable model, OH40 was not independently associated with 5-CST time after controlling for age (p > 0.05). Worse performance on the chair stands test was however an independent predictor of OI (odds ratio 1.06, p = 0.039).

Conclusion

Longer time taken on the 5-CST, a marker of sarcopenia, was an independent predictor of OI in a large population study. The relationship between sarcopenia and orthostatic blood pressure response is not well elucidated. We plan to further investigate this area in a future clinical cohort.

123 ACUTE-PHASE BED-REST DURATION WAS ASSOCIATED WITH LOWER GRIP STRENGTH IN A POST-COVID-19 COHORT

Background

Though age-related muscle loss is traditionally associated with older cohorts, strong evidence suggests a life-spanning precipitation of decreasing muscle mass and strength beginning as early as the fourth decade of life, with established deleterious consequences for later-life morbidity and mortality. Periods of low activity and bed rest (LA/BR) can further compound this depletion of muscle strength. Our aim was to examine such associations in a post-COVID-19 cohort.

Methods

Participants reporting ongoing symptomatology and fatigue post COVID-19 underwent assessments of grip strength via hand-held dynamometry (2 measures on each hand). Demographics of COVID-19 illness, including time since diagnosis, duration of LA/BR during acute illness, and levels of fatigue were captured via self-reported questionnaires. Independent predictors of mean grip strength were investigated using a linear regression model.

Results

Forty-nine participants underwent assessments (69% female, mean age 44(12) years). At the time of assessment, days post COVID-19 diagnosis ranged from 39–522 (mean 262(140)). The mean self-reported period of LA/BR during the acute illness was 15(18) days. In general, participants reported significant levels of fatigue (median Chalder Fatigue Scale score 22(8)). Mean grip strength was 41.3(6.3) Kg for men and 22.8(6.7) Kg for women. When predictors of grip strength were investigated, an increased duration of LA/BR was found to be associated with lower grip strength, independently of age, gender, time since COVID-19 diagnosis, and self-reported fatigue (Beta = −0.158, 95% Confidence Interval − 0.242 to −0.074, p = 0.001).

Conclusion

In this cohort, every day of LA/BR during acute COVID-19 illness was independently associated with subsequent lower grip strength of approximately 150 g. These results underscore the importance of early mobilization and discouraging bed rest in the acute phase of COVID-19. Patients who are isolating should be encouraged to maintain physical activity and muscle strength as part of a modified isolation-friendly rehabilitation programme.