Integrating muscle cell biochemistry and whole-body physiology in humans:(31)P-MRS data from the InSight trial

A Systematic Review and Meta-Analysis of Tai Chi Training in Cardiorespiratory Fitness of Elderly People

Objectives

The purpose of this study was to investigate the influence of Tai Chi on cardiorespiratory fitness (CRF) in elderly people using meta-analysis.

Methods

This study used seven electronic databases and data retrieved from randomized controlled trials (RCTs) investigating the role of Tai Chi on CRF in the elderly. All these 24 RCTs were screened and selected from 7 literature databases. The Stata 11.2 software (StataCorp, USA) was used for the meta-analysis, subgroup analysis, and bias test, while the Cochrane Collaboration's tool was used for the assessment of the risk of bias (RoB). 4 researchers independently participated in sample selection, data extraction, and RoB assessment.

Results

Following the inclusion criteria, 24 eligible studies were included in our analysis. The meta-analysis indicated that Tai Chi practice significantly increased the maximum rate of oxygen consumption (VO_{2 max}) (weighted mean difference (WMD)  = 3.76, 95% CI: 1.25 to 6.26, P < 0.1), leading to an overall reduction in the heart rate (HR) (WMD  = −1.84, 95% CI: −2.04 to −1.63, P  ≤ 0.001) and an increase in the O_{2 pulse} (WMD = 0.94, 95% CI: 0.60 to 1.28, P ≤ 0.001) in individuals who practiced Tai Chi regularly compared with those who did not. The subgroup analysis suggested that overall in those who practiced Tai Chi, males (WMD = 1.48, 95% CI: 0.85 to 2.12, P ≤ 0.001) had higher O_{2 pulse} than females (WMD = 0.73, 95% CI: 0.33 to 1.12, P ≤ 0.001). The subgroup analysis also showed an increase in the vital capacity (VC) (WMD = 316.05, 95% CI: 239.74 to 392.35, P ≤ 0.001) in individuals practicing Tai Chi. When the samples were further stratified by Tai Chi practicing time, the subgroup analysis suggested that individuals practicing Tai Chi over a period of 24 weeks showed no significant difference in VC (WMD = 82.95, 95% CI: -98.34 to 264.23, P=0.370), while those practicing Tai Chi over a period of 48 weeks showed a significant increase (WMD = 416.62, 95% CI: 280.68 to 552.56, P ≤ 0.001). Furthermore, the subgroup analysis demonstrated that the increase in VC is significantly correlated with the Tai Chi practicing time (WMD = 344.97, 95% CI: 227.88 to 442.06, P ≤ 0.001).

Conclusion

Regular Tai Chi practice could improve the CRF in the elderly, as indicated by significant improvement in indicators including VO_2max, O_2pulse, VC, and HR. However, gender and practice time might influence the overall beneficial outcomes.

Greater Skeletal Muscle Oxidative Capacity Is Associated With Higher Resting Metabolic Rate: Results From the Baltimore Longitudinal Study of Aging

Resting metabolic rate (RMR) tends to decline with aging. The age-trajectory of decline in RMR is similar to changes that occur in muscle mass, muscle strength, and fitness, but while the decline in these phenotypes has been related to changes of mitochondrial function and oxidative capacity, whether lower RMR is associated with poorer mitochondrial oxidative capacity is unknown. In 619 participants of the Baltimore Longitudinal Study of Aging, we analyzed the cross-sectional association between RMR (kcal/day), assessed by indirect calorimetry, and skeletal muscle maximal oxidative phosphorylation capacity, assessed as postexercise phosphocreatine recovery time constant (τ PCr), by phosphorous magnetic resonance spectroscopy. Linear regression models were used to evaluate the relationship between τ PCr and RMR, adjusting for potential confounders. Independent of age, sex, lean body mass, muscle density, and fat mass, higher RMR was significantly associated with shorter τ PCr, indicating greater mitochondrial oxidative capacity. Higher RMR is associated with a higher mitochondrial oxidative capacity in skeletal muscle. This association may reflect a relationship between better muscle quality and greater mitochondrial health.

Molecular correlates of MRS-based 31 phosphocreatine muscle resynthesis rate in healthy adults

Dynamic phosphorus MRS (³¹ P-MRS) is a method used for in vivo studies of skeletal muscle energetics including measurements of phosphocreatine (PCr) resynthesis rate during recovery of submaximal exercise. However, the molecular events associated with the PCr resynthesis rate are still under debate. We assessed vastus lateralis PCr resynthesis rate from ³¹ P-MRS spectra collected from healthy adults as part of the CALERIE II study (caloric restriction), and assessed associations between PCr resynthesis and muscle mitochondrial signature transcripts and proteins (NAMPT, NQO1, PGC-1α, and SIRT1). Regression analysis indicated that higher concentration of nicotinamide phosphoribosyltransferase (NAMPT) protein, a mitochondrial capacity marker, was associated with faster PCr resynthesis. However, PCr resynthesis was not associated with greater physical fitness (VO₂ peak) or messenger ribonucleic acid levels of mitochondrial function markers such as NQO1, PGC-1α, and SIRT1, suggesting that the impact of these molecular signatures on PCr resynthesis may be minimal in the context of an acute exercise bout. Together, these findings suggest that ³¹ P-MRS based PCr resynthesis may represent a valid non-invasive surrogate marker of mitochondrial NAMPT in human skeletal muscle.

Magnetic Resonance Imaging of Phosphocreatine and Determination of BOLD Kinetics in Lower Extremity Muscles using a Dual-Frequency Coil Array

Magnetic resonance imaging (MRI) provides the unique ability to study metabolic and microvasculature functions in skeletal muscle using phosphorus and proton measurements. However, the low sensitivity of these techniques can make it difficult to capture dynamic muscle activity due to the temporal resolution required for kinetic measurements during and after exercise tasks. Here, we report the design of a dual-nuclei coil array that enables proton and phosphorus MRI of the human lower extremities with high spatial and temporal resolution. We developed an array with whole-volume coverage of the calf and a phosphorus signal-to-noise ratio of more than double that of a birdcage coil in the gastrocnemius muscles. This enabled the local assessment of phosphocreatine recovery kinetics following a plantar flexion exercise using an efficient sampling scheme with a 6 s temporal resolution. The integrated proton array demonstrated image quality approximately equal to that of a clinical state-of-the-art knee coil, which enabled fat quantification and dynamic blood oxygen level-dependent measurements that reflect microvasculature function. The developed array and time-efficient pulse sequences were combined to create a localized assessment of calf metabolism using phosphorus measurements and vasculature function using proton measurements, which could provide new insights into muscle function.

Physical activity, mental health, and weight gain in a longitudinal observational cohort of nonobese young adults

OBJECTIVE

To investigate the relationship among moderate-to-vigorous physical activity (MVPA), mental health symptoms, and weight gain in young adults.

METHODS

Fifty-nine healthy men and women (age 26.8 ± 4.7 years, body mass index [BMI] 22.4 ± 2.3 kg/m(2) ) were assessed at baseline and year 2. Weight, BMI, fat mass by dual-energy X-ray absorptiometry, anxiety and depression by the SCL-90, and MVPA by accelerometry were assessed. Sex-stratified linear regression models were used to examine associations between baseline anxiety/depression and body composition change, then repeated controlling for baseline MVPA.

RESULTS

Overall, weight, BMI, fat mass, and subcutaneous adiposity significantly increased at year 2 (P < 0.05). For women, a higher depression and anxiety score predicted increased weight, BMI, fat mass, and subcutaneous adiposity (P < 0.05). Controlling for MVPA attenuated these associations to nonsignificance. For men, MVPA did not alter the associations between anxiety and increased weight, BMI, fat mass, and subcutaneous adiposity (P < 0.05) or the associations between depression and decreased weight, BMI, fat mass, and subcutaneous adiposity (P < 0.05).

CONCLUSIONS

Anxiety and depression were related to body composition change for young adults. In women, MVPA attenuated these associations to nonsignificance. MVPA may buffer the adverse effects of depression and anxiety symptoms on young women's weight gain.

31P Magnetic Resonance Spectroscopy Assessment of Muscle Bioenergetics as a Predictor of Gait Speed in the Baltimore Longitudinal Study of Aging

BACKGROUND

Aerobic fitness and muscle bioenergetic capacity decline with age; whether such declines explain age-related slowing of walking speed is unclear. We hypothesized that muscle energetics and aerobic capacity are independent correlates of walking speed in simple and challenging performance tests and that they account for the observed age-related decline in walking speed in these same tests.

METHODS

Muscle bioenergetics was assessed as postexercise recovery rate of phosphocreatine (PCr), k _PCr, using phosphorus magnetic resonance spectroscopy (³¹P-MRS) in 126 participants (53 men) of the Baltimore Longitudinal Study of Aging aged 26-91 years (mean = 72 years). Four walking tasks were administered-usual pace over 6 m and 150 seconds and fast pace over 6 m and 400 m. Separately, aerobic fitness was assessed as peak oxygen consumption (peak VO₂) using a graded treadmill test.

RESULTS

All gait speeds, k _PCr, and peak VO₂ were lower with older age. Independent of age, sex, height, and weight, both k _PCr and peak VO₂ were positively and significantly associated with fast pace and long distance walking but only peak VO₂ and not k _PCr was significantly associated with usual gait speed over 6 m. Both k _PCr and peak VO₂ substantially attenuated the association between age and gait speed for all but the least stressful walking task of 6 m at usual pace.

CONCLUSION

Muscle bioenergetics assessed using ³¹P-MRS is highly correlated with walking speed and partially explains age-related poorer performance in fast and long walking tasks.

Quantification of skeletal muscle mitochondrial function by 31P magnetic resonance spectroscopy techniques: a quantitative review

Magnetic resonance spectroscopy (MRS) can give information about cellular metabolism in vivo which is difficult to obtain in other ways. In skeletal muscle, non-invasive (31) P MRS measurements of the post-exercise recovery kinetics of pH, [PCr], [Pi] and [ADP] contain valuable information about muscle mitochondrial function and cellular pH homeostasis in vivo, but quantitative interpretation depends on understanding the underlying physiology. Here, by giving examples of the analysis of (31) P MRS recovery data, by some simple computational simulation, and by extensively comparing data from published studies using both (31) P MRS and invasive direct measurements of muscle O2 consumption in a common analytical framework, we consider what can be learnt quantitatively about mitochondrial metabolism in skeletal muscle using MRS-based methodology. We explore some technical and conceptual limitations of current methods, and point out some aspects of the physiology which are still incompletely understood.