Blood pressure and cognitive function: the role of central aortic and brachial pressures

Central (aortic) blood pressures differ from brachial pressures and may be more relevant to the study of cognitive function, given that blood is delivered to the brain through the central large arteries. Pulse-pressure amplification reflects the augmentation of blood pressure between the central and peripheral arteries, which diminishes with aging. We aimed to determine the association between central blood pressure and cognitive function in independently living adults aged 20 to 82 years (N = 493). In adjusted regression models, higher central systolic pressure and higher central pulse pressure were each associated with poorer processing speed, Stroop processing, and recognition memory. Lower amplification was associated with poorer Stroop processing, working memory, and recognition memory. Higher brachial systolic pressure and brachial pulse pressure were both associated with poorer Stroop processing. In summary, central pressures and amplification were sensitive indicators of cognitive aging, predicting aspects of cognitive performance not predicted by brachial blood pressure.

Influence of vibration resistance training on knee extensor and plantar flexor size, strength, and contractile speed characteristics after 60 days of bed rest

Spaceflight and bed rest (BR) result in loss of muscle mass and strength. This study evaluated the effectiveness of resistance training and vibration-augmented resistance training to preserve thigh (quadriceps femoris) and calf (triceps surae) muscle cross-sectional area (CSA), isometric maximal voluntary contraction (MVC), isometric contractile speed, and neural activation (electromyogram) during 60 days of BR. Male subjects participating in the second Berlin Bed Rest Study underwent BR only [control (CTR), n = 9], BR with resistance training (RE; n = 7), or BR with vibration-augmented resistance training (RVE; n = 7). Training was performed three times per week. Thigh CSA and MVC torque decreased by 13.5 and 21.3%, respectively, for CTR (both P < 0.001), but were preserved for RE and RVE. Calf CSA declined for all groups, but more so (P < 0.001) for CTR (23.8%) than for RE (10.7%) and RVE (11.0%). Loss in calf MVC torque was greater (P < 0.05) for CTR (24.9%) than for RVE (12.3%), but not different from RE (14.8%). Neural activation at MVC remained unchanged in all groups. For indexes related to rate of torque development, countermeasure subjects were pooled into one resistance training group (RT, n = 14). Thigh maximal rate of torque development (MRTD) and contractile impulse remained unaltered for CTR, but MRTD decreased 16% for RT. Calf MRTD remained unaltered for both groups, whereas contractile impulse increased across groups (28.8%), despite suppression in peak electromyogram (12.1%). In conclusion, vibration exposure did not enhance the efficacy of resistance training to preserve thigh and calf neuromuscular function during BR, although sample size issues may have played a role. The exercise regimen maintained thigh size and MVC strength, but promoted a loss in contractile speed. Whereas contractile speed improved for the calf, the exercise regimen only partially preserved calf size and MVC strength. Modification of the exercise regimen seems warranted.

Enhanced physiological tremor deteriorates plantar flexor torque steadiness after bed rest

This study evaluated the effectiveness of resistance training to preserve submaximal plantar flexor (PF) torque steadiness following 60 days of bed rest (BR). Twenty-two healthy male subjects underwent either BR only (CTR, n=8), or BR plus resistance training (RT, n=14). The magnitude of torque fluctuations during steady submaximal isometric PF contractions (20%, 40%, 60% and 80% of maximum) were assessed before and after BR. Across contraction intensities, torque fluctuations (coefficient of variation, CV) increased more (P<0.05) after BR for CTR (from 0.31±0.10 to 0.92±0.63; P<0.001), than for RT (from 0.30±0.09 to 0.54±0.27; P<0.01). A shift in the spectral content of torque fluctuations towards increased rhythmic activity between 6.5 and 20Hz was observed in CTR only (P<0.05). H-reflex amplitude (H(max)/M(max) ratio) declined across groups from 0.57±0.18 before BR to 0.44±0.14 following BR (P<0.01) without correlation to CV. The present study showed that increased torque fluctuation after BR resulted from enhanced physiological tremor. Resistance training prevented the spectral shift in isometric PF torque fluctuation and offset ∼50% of the decline in performance associated with long-term BR.

Effects of hyperbaric (6 ATA) pressure on voluntary and evoked skeletal muscle contractile properties

The objective of this study was to investigate the effect of 6 atmospheres of pressure (ATA) on plantar flexors' (PF) voluntary force and activation, force-frequency characteristics, and rate of torque development (RTD). Eight subjects performed PF isometric contractions. Muscle activation was monitored by electromyographic (EMG) activity (PF and dorsiflexors) and the interpolated twitch technique (ITT). Maximal evoked contractions of the PF were elicited at 1, 2, 3, 5, 10, 20, and 40 Hz. PF RTD was calculated with maximal voluntary, 1 and 40 Hz contractions. Hyperbaric pressures significantly decreased PF voluntary torque; 6.2%, ITT activation; 2.8% with a trend for a 19.1% decrease in EMG (p = 0.1). There were no significant differences in the dorsiflexors/PF EMG ratio. One Hz torque was potentiated 15.7% with an increased absolute RTD of 12.8%, but no change in relative RTD. The results suggested hyperbaric-induced decreases in PF activation contributed to voluntary torque loss. A lack of torque reduction with higher frequency tetanic stimulation (2-40 Hz) suggested that 6 ATA does not impair myofilament kinetics, whereas twitch potentiation may include changes in excitation-contraction coupling.