Central Cardiorespiratory And Peripheral Metabolic Influences On Kinetics Of Oxygen Uptake In Older Humans

The purpose of this thesis was to determine which factors influence oxygen uptake (VO{dollar}\sb2){dollar} kinetics during exercise in old individuals. These factors may include central {dollar}\rm O\sb2{dollar} delivery (i.e. cardiac output kinetics), the rate of O{dollar}\sb2{dollar} delivery at the exercising muscle, and the rate at which mitochondria can use O{dollar}\sb2.{dollar} Fitness level may also influence VO{dollar}\sb2{dollar} kinetics, by affecting the above factors. These factors were estimated by measuring heart rate (HR) kinetics, muscle capillarization, and citrate synthase (CS) activity, respectively, in groups of old ({dollar}\sim{dollar}65y) and young ({dollar}\sim{dollar}26y) individuals. Capillarization and CS activity of the lateral gastrocnemius were compared to VO{dollar}\sb2{dollar} an PCr kinetics (which reflect kinetics of muscle O{dollar}\sb2{dollar} consumption), measured during ankle plantar flexion, while HR kinetics were compared to VO{dollar}\sb2{dollar} kinetics during plantar flexion, cycling, and treadmill exercise. The influence of fitness levels on VO{dollar}\sb2{dollar} kinetics during cycling was also assessed in old an young groups of individuals. Old and young individuals had similar measures for capillarization, CS activity, and HR, PCr, and VO{dollar}\sb2{dollar} kinetics during plantar flexion exercise, compared to young adults. Old individuals, who were relatively fit for their age, had VO{dollar}\sb2{dollar} kinetics which were similar to fit young subjects.;These studies show that peripheral muscle oxidative capacity (as determined by enzyme activities, capillarization and PCr dynamics), and VO{dollar}\sb2{dollar} kinetics during exercise of a small muscle mass (plantar flexors), accustomed to daily activity, are maintained with age. Cardiorespiratory kinetics of the old individuals are slower during exercise involving large muscle mass (i.e. treadmill walking or cycling), which places a greater demand on central O{dollar}\sb2{dollar} delivery; however these kinetics can be greatly improved with moderate improvements in fitness level.;It is speculated that peripheral oxidative capacity (i.e. mitochondrial capacity or capillarization) is dominant in controlling VO{dollar}\sb2{dollar} kinetics during exercise of a small muscle mass in old individuals, since these measures were similar, along with VO{dollar}\sb2{dollar} kinetics, in the old compared to yound subjects. Central O{dollar}\sb2{dollar} transport (cardiac output kinetics, as estimated by HR kinetics) appears to limit VO{dollar}\sb2{dollar} kinetics during larger muscle mass exercise (cycling and treadmill walking) in older individuals

Anthropometric and physiological predictors of flat-water 1000 m kayak performance in young adolescents and the effectiveness of a high volume training camp.

Our purpose was to determine the relationship of anthropometric and physiological variables with 1000m flat-water kayak (K1000) performance. A secondary purpose was to determine the effectiveness of a high volume training camp. High performance young adolescent kayakers (n=13, 8 males, 5 females, 15±1 yrs) participated in this study. Testing before and after the 3-4 week training camp included anthropometric measurements (height, sitting height, arm span, and body mass), strength (1-RM: bench press and bench pull), flexibility (sit and reach), and an incremental kayak ergometer test to determine peak oxygen uptake (VO2peak) and anaerobic threshold, and an open water K1000 time trial. K1000 time was significantly correlated with height (r=-0.81; p\u3c0.01), sitting height (r=-0.85; p\u3c0.01), arm span (r=-0.87; p\u3c0.01), bench press (r=-0.92; p\u3c0.01), bench pull (r=-0.85; p\u3c0.01), VO2peak (r=-0.87; p\u3c0.01) and anaerobic threshold (r=-0.83; p\u3c0.05). Following the training camp there were no significant differences in body mass, strength, and VO2 peak, however, anaerobic threshold (33.6±6.2 to 42.3±8.8 ml•kg-1•min-1, p=0.001) and K1000 (302±44 to 289±31 sec, p=0.007) significantly improved. The results of this study suggest that K1000 performance in young adolescent kayakers appears to require a high aerobic and strength contribution and that a high volume training camp is effective for improving anaerobic threshold and performance

Calreticulin signals upstream of calcineurin and MEF2C in a critical Ca2+-dependent signaling cascade

We uncovered a new pathway of interplay between calreticulin and myocyte-enhancer factor (MEF) 2C, a cardiac-specific transcription factor. We establish that calreticulin works upstream of calcineurin and MEF2C in a Ca2+-dependent signal transduction cascade that links the endoplasmic reticulum and the nucleus during cardiac development. In the absence of calreticulin, translocation of MEF2C to the nucleus is compromised. This defect is reversed by calreticulin itself or by a constitutively active form of calcineurin. Furthermore, we show that expression of the calreticulin gene itself is regulated by MEF2C in vitro and in vivo and that, in turn, increased expression of calreticulin affects MEF2C transcriptional activity. The present findings provide a clear molecular explanation for the embryonic lethality observed in calreticulin-deficient mice and emphasize the importance of calreticulin in the early stages of cardiac development. Our study illustrates the existence of a positive feedback mechanism that ensures an adequate supply of releasable Ca2+ is maintained within the cell for activation of calcineurin and, subsequently, for proper functioning of MEF2C

A dental stool with chest support reduces lower back muscle activation

Activation of back musculature during work tasks leads to fatigue and potential injury. This is especially prevalent in dentists who perform much of their work from a seated position. We examined the use of an ergonomic dental stool with mid-sternum chest support for reducing lower back muscle activation. Electromyography of lower back extensors was assessed from 30 dental students for 20 s during three conditions in random order: (a) sitting upright at 90° of hip flexion on a standard stool, (b) leaning forward at 80° of hip flexion on a standard stool, and (c) leaning forward at 80° of hip flexion while sitting on an ergonomic stool. Muscular activity of the back extensors was reduced when using the ergonomic stool compared to the standard stool, by 33-50% (p < 0.01). This suggests a potential musculoskeletal benefit with use of a dental stool with mid-sternum chest support

Effect of Resistance Training on Microvascular Density and eNOS Content in Skeletal Muscle of Sedentary Men

The effects of resistance training (RT) on muscle mass, strength and insulin sensitivity are well established, but the underlying mechanisms are only partially understood. The main aim of this study is to investigate whether RT induces changes in endothelial enzymes of the muscle microvasculature, which would increase NO bioavailability and could contribute to improved insulin sensitivity. Eight previously sedentary males (age 20±0.4y, BMI 24.5±0.9 kg.m-2) completed 6wk of RT 3x/week. Muscle biopsies were taken from the m. vastus lateralis and microvascular density and endothelial specific eNOS content, eNOS Ser1177 phosphorylation and NOX2 content were assessed pre- and post-RT using quantitative immunofluorescence microscopy. Whole body insulin sensitivity (measured as Matsuda Index), microvascular filtration capacity (functional measure of the total available endothelial surface area) and arterial stiffness (augmentation index, central and peripheral pulse wave velocity) were also measured. Measures of microvascular density, microvascular filtration capacity, microvascular eNOS content, basal eNOS phosphorylation and endothelial NOX2 content did not change from pre-RT to post-RT. RT increased insulin sensitivity (P <0.05) and reduced resting blood pressure and augmentation index (P <0.05), but did not change central or peripheral pulse wave velocity. In conclusion RT did not change any measure of muscle microvascular structure or function

Effect of heavy-intensity 'priming' exercise on oxygen uptake and muscle deoxygenation kinetics during moderate-intensity step-transitions initiated from an elevated work rate

We examined the effect of heavy-intensity ‘priming’ exercise on the rate of adjustment of pulmonary O2 uptake (τ 2p) initiated from elevated intensities. Fourteen men (separated into two groups: τ 2p≤25s [Fast] or τ 2p>25s [Slow]) completed step-transitions from 20W-to- 45%lactate threshold (LT; lower-step, LS) and 45%-to-90%LT (upper-step, US) performed (i) without; and (ii) with US preceded by heavy-intensity exercise (HUS). Breath-by-breath 2p and near-infrared spectroscopy-derived muscle deoxygenation ([HHb+Mb]) were measured. Compared to LS, τ 2p was greater (p0.05) from LS or Fast group US. In Slow, τ[HHb+Mb] increased (p<0.05) in US relative to HUS; this finding coupled with a reduced τ 2p indicates a priming-induced improvement in matching of muscle O2 delivery-to-O2 utilization during transitions from elevated intensities in those with Slow but not Fast 2p kinetics