Relationships between lower body strength and the energy cost of treadmill walking in a cohort of healthy older adults: a cross-sectional analysis

Abstract

Purpose

Gait speed is associated with survival in older adults and it was suggested that an elevated energy cost of walking (Cw) is an important determinant of gait speed reduction. Thus far, little is known about the factors that contribute to a lower Cw but it was shown that lower body strength training could reduce the Cw. Therefore, the objective of this study was to investigate the relationship between lower body strength and the Cw in a cohort of healthy older adults.

Methods

A total of 48 participants were included in this study (70.7 ± 5.4 years). After a geriatric and a neuropsychological assessment, participants underwent a fitness testing protocol which included a maximal oxygen uptake test, assessment of the Cw at 4 km h⁻¹ on a treadmill, an isokinetic maximal strength test for the ankle, knee and hip joints and a body composition assessment. Relationships between strength variables and the Cw were assessed with partial correlations and linear regression analyses.

Results

Hip extensors and hip flexors peak torque was significantly correlated with the Cw (r = −0.36 and −0.32, respectively; p < 0.05). A tendency towards significance was identified for the ankle plantar flexors (r = −0.25, p = 0.09). Hip extensors peak torque was the only significant neuromuscular parameter included in the linear regression analysis (p < 0.05).

Conclusion

These results show that hip extensors are an important muscle group with regards to the Cw measured on a treadmill in this cohort of healthy older adults.

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Neural, biomechanical, and physiological factors involved in sex-related differences in the maximal rate of isometric torque development

Abstract

Objective

Recent research has reported that lower maximal rate of torque development (dτ/dt _max) exhibited by females, relative to males, during knee extension can be accounted for by normalization to a maximal voluntary contraction (MVC); however, this was not seen in the upper limb.

Purpose

The aim of the current work was to examine the contribution of maximum strength (τ_max), twitch contraction time (CT), muscle fiber condition velocity (MFCV), and rate of muscle activation (Q₃₀) to sex-differences in the dτ/dt _max during maximal isometric dorsiflexion.

Methods

Thirty-eight participants (20 males; 18 females) performed both maximal voluntary and evoked isometric contractions of the tibialis anterior across 3 days. Ten maximal compound muscle action potentials were elicited and subsequently followed by three, 5-s contractions. From the recordings, MFCV, dτ/dt _max, τ_max, CT, electromechanical delay (EMD), root-mean squared (RMS) amplitude, peak-to-peak voltage (Vpp), and Q₃₀ were calculated.

Results

An ANCOVA showed that τ_max accounted for all the sex-differences in dτ/dt _max (p = 0.96). There were no significant differences between groups with respect to MFCV, RMS amplitude, Vpp amplitude, or CT. However, there was a significant sex-difference in dτ/dt _max, τ_max, and Q₃₀. Females had longer evoked EMD times compared with males (15.69 ± 10.57 ms versus 9.95 ± 3.46 ms; p = 0.01), but the voluntary EMD times were not different.

Conclusion

The current research supports the work by Hannah et al. Exp Physiol 97:618–629, (2012) that normalization to MVC in the quadriceps is able to account for all sex-differences in rate of toque development in the lower limb.

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The CgHaa1-Regulon Mediates Response and Tolerance to Acetic Acid Stress in the Human Pathogen Candida glabrata

To thrive in the acidic vaginal tract C. glabrata has to cope with high concentrations of acetic acid. The mechanisms underlying C. glabrata tolerance to acetic acid at low pH remain largely uncharacterized. In this work it is demonstrated the essential role of the CgHaa1 transcription factor (encoded by ORF CAGL0L09339g) in the response and tolerance of C. glabrata to acetic acid. Transcriptomic analysis showed that CgHaa1 regulates, directly or indirectly, the expression of about 75% of the genes activated under acetic acid stress. CgHaa1-activated targets are involved in multiple physiological functions including membrane transport, metabolism of carbohydrates and amino acids, regulation of the activity of the plasma membrane H⁺-ATPase and adhesion. Under acetic acid stress CgHaa1 increased the activity and the expression of the CgPma1 proton pump and contributed to increased colonization of vaginal epithelial cells by C. glabrata. CgHAA1, CgTPO3 and CgHSP30, two identified CgHaa1-activated targets, are herein demonstrated to be determinants of C. glabrata tolerance to acetic acid. The protective effect of CgTpo3 and of CgHaa1 was linked to a role of these proteins in reducing the accumulation of acetic acid inside C. glabrata cells. In response to acetic acid stress, marked differences were found in the regulons controlled by CgHaa1 and by its S. cerevisiae ScHaa1 ortholog, demonstrating a clear divergent evolution of the two regulatory networks. The results gathered in this study significantly advance the understanding of the molecular mechanisms underlying the success of C. glabrata as a vaginal colonizer.

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The First Scube3 Mutant Mouse Line with Pleiotropic Phenotypic Alterations

The vertebrate Scube (Signal peptide, CUB and EGF-like domain-containing protein) family consists of three independent members Scube1-3, which encode secreted cell surface-associated membrane glycoproteins. Limited information about the general function of this gene family is available, and their roles during adulthood. Here, we present the first Scube3 mutant mouse line (Scube3^N294K/N294K) that clearly shows phenotypic alterations by carrying a missense mutation in exon 8, and thus contributes to understand SCUBE3 functions. We performed a detailed phenotypic characterization in the German Mouse Clinic (GMC). Scube3^N294K/N294K mutants showed morphological abnormalities of the skeleton, alterations of parameters relevant for bone metabolism, changes in renal function and hearing impairments. These findings correlate with characteristics of the rare metabolic bone disorder Paget disease of bone (PDB), associated with the chromosomal region of human SCUBE3. In addition, alterations in energy metabolism, behavior and neurological functions were detected in Scube3^N294K/N294K mice. The Scube3^N294K/N294K mutant mouse line may serve as a new model for further studying the effect of impaired SCUBE3 gene function.

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Could small-diameter muscle afferents be responsible for the ergogenic effect of limb ischemic preconditioning?

N/A

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INTERMITTENT PARATHYROID HORMONE ADMINISTRATION ATTENUATES ENDOTHELIAL DYSFUNCTION IN OLD RATS

Aging is an independent risk factor for cardiovascular disease and is characterized by a decline in endothelial function. Parathyroid hormone (PTH) administration has been shown to increase endothelial nitric oxide synthase (eNOS) expression. The purpose of this investigation was to determine the effect of intermittent PTH administration on aortic endothelial function in old rodents. We hypothesized that intermittent PTH administration would improve endothelial function in older rodents. Old (24 mo) and young (4 mo) Fischer-344 rats were given 10 injections of PTH (1-34) (43 μg/kg/day) or phosphate buffered saline (100 μl/day) over 15 days. Endothelium-dependent relaxation of aortic rings in response to acetylcholine (10^-9-10^-5 M) was significantly impaired in old control (OC) compared to young control (YC) as indicated by a reduced area under the curve (AUC, 100 ± 6.28 vs. 54.08 ± 8.3%; P < 0.05) and impaired maximal relaxation (E_max, 70.1 ± 4.48 vs. 92.9 ± 4.38%; P < 0.05). E_max was improved in old animals treated with PTH (OPTH) (OC, 70.1 ± 4.48 vs. OPTH, 85 ± 7.48%; P < 0.05) as well as AUC (OC, 54.08 ± 8.3 vs. OPTH 82.5 ± 5.7%; P < 0.05) while LogEC₅₀ was not different. Endothelial-independent relaxation in response to sodium nitroprusside was not different among groups. Aortic eNOS protein expression was significantly decreased in OC compared to YC (P < 0.05). PTH treatment restored eNOS expression in OPTH animals (P < 0.05). These data suggest PTH may play a role in attenuating age-related impairments in aortic endothelial function.

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Nasal High Flow therapy reduces work of breathing compared to oxygen during sleep in COPD and smoking controls - prospective observational study.

Rationale: Patients with COPD endure excessive resistive and elastic loads leading to chronic respiratory failure. Oxygen supplementation corrects hypoxemia but is not expected to reduce mechanical loads. Nasal High Flow therapy (NHF) supports breathing by reducing dead space but it is unclear how it affects mechanical loads of patients with COPD. Objective: To compare the effects of low-flow oxygen and NHF on ventilation and work of breathing (WOB) in patients with COPD and controls during sleep. Methods: Patients with COPD (n=12) and controls (n=6) were recruited and submitted to polysomnography to measure sleep parameters and ventilation in response to administration of oxygen and NHF. A subset of 6 patients also had an esophageal catheter inserted for measuring WOB. Results: Patients with COPD had similar minute ventilation, but lower tidal volumes than matched controls. Under oxygen, SaO₂ was increased and minute ventilation was reduced in both controls and patients with COPD, but with an increase in transcutaneous CO₂ levels. NHF produced a greater reduction in minute ventilation, and was associated with a reduction in CO₂ levels. While NHF halved WOB, oxygen produced only minor reduction in this parameter. Conclusion: Oxygen produced little changes in WOB, which were associated with CO₂ elevations. On the other hand, NHF produced a large reduction in minute ventilation and WOB with a concomitant fall in CO₂ levels. Our data indicate that NHF improves alveolar ventilation during sleep compared to oxygen and room-air in patients with COPD and therefore can decrease their cost of breathing.

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