Electrically induced quadriceps fatigue in the contralateral leg impairs ipsilateral knee extensors performance.

Muscle fatigue induced by voluntary exercise, which requires central motor drive, causes central fatigue that impairs endurance performance of a different, nonfatigued muscle. This study investigated the impact of quadriceps fatigue induced by electrically induced (no central motor drive) contractions on single-leg knee-extension (KE) performance of the subsequently exercising ipsilateral quadriceps. On two separate occasions, eight males completed constant-load (85% of maximal power-output) KE exercise to exhaustion. In a counterbalanced manner, subjects performed the KE exercise with no pre-existing quadriceps fatigue in the contralateral leg on one day (No-PreF), whereas on the other day, the same KE exercise was repeated following electrically induced quadriceps fatigue in the contralateral leg (PreF). Quadriceps fatigue was assessed by evaluating pre- to postexercise changes in potentiated twitch force (ΔQtw,pot; peripheral fatigue), and voluntary muscle activation (ΔVA; central fatigue). As reflected by the 57 ± 11% reduction in electrically evoked pulse force, the electrically induced fatigue protocol caused significant knee-extensors fatigue. KE endurance time to exhaustion was shorter during PreF compared with No-PreF (4.6 ± 1.2 vs 7.7 ± 2.4 min; P < 0.01). Although ΔQtw,pot was significantly larger in No-PreF compared with PreF (-60% vs -52%, P < 0.05), ΔVA was greater in PreF (-14% vs -10%, P < 0.05). Taken together, electrically induced quadriceps fatigue in the contralateral leg limits KE endurance performance and the development of peripheral fatigue in the ipsilateral leg. These findings support the hypothesis that the crossover effect of central fatigue is mainly mediated by group III/IV muscle afferent feedback and suggest that impairments associated with central motor drive may only play a minor role in this phenomenon.

The Vascular Side of Chronic Bed Rest: When a Therapeutic Approach Becomes Deleterious.

The interplay between chronic constraint and advanced aging on blood flow, shear-rate, vascular function, nitric oxide (NO)-bioavailability, microcirculation, and vascular inflammation factors is still a matter of debate. Ninety-eight individuals (Young, n=28, 23±3yrs; Old, n=36, 85±7yrs; Bedridden, n=34, 88±6yrs) were included in the study. The bedridden group included old individuals chronically confined to bed (3.8±2.3yrs). A blood sample was collected and analyzed for plasma nitrate, and vascular inflammatory markers. Hyperemic response (∆peak) during the single passive leg movement (sPLM) test was used to measure vascular function. Skeletal muscle total hemoglobin was measured at the vastus lateralis during the sPLM test, by means of near infrared spectroscopy (NIRS). Bedridden subjects revealed a depletion of plasma nitrates compared with Old (-23.8%) and Young (-31.1%). Blood flow was lower in the Bedridden in comparison to Old (-20.1%) and Young (-31.7%). Bedridden presented lower sPLM ∆peak compared Old (-72.5%) and the Young (-83.3%). ∆peak of NIRS total hemoglobin was lower in the Bedridden compared to that in the Young (-133%). All vascular inflammatory markers except IL-6 were significantly worse in the Bedridden compared to Old and Young. No differences were found between the Old and Young in inflammatory markers. Results of this study confirm that chronic physical constraint induces an exacerbation of vascular disfunction and differential regulation of vascular-related inflammatory markers. The mechanisms involved in these negative adaptations seems to be associated with endothelial dysfunction and consequent diminished NO-bioavailability likely caused by the reduced shear-rate consequential to long-term reduction of physical activity.

Role of Exercise in Vascular Function and Inflammatory Profile in Age-Related Obesity.

In western countries, aging is often accompanied by obesity and age-related obesity is characterized by vascular dysfunction and a low-grade inflammatory profile. Exercise is a nonpharmacological strategy able to decrease the development and incidence of risk factors for several health-threatening diseases. Nonetheless, its long-term effect on vascular function and inflammation in age-related obesity is still unclear. The aim of this study was to investigate the effect of regular, supervised exercise on inflammatory profile and vascular function in age-related obesity. We also hypothesized that vascular function and inflammatory profile would have been correlated in overweight and obese individuals. Thirty normal weight (NW; 70 ± 5 years, 23.9 ± 2.6 BMI) and forty overweight and obese elderly (OW&OB; 69 ± 5 years, 30.1 ± 2.3 BMI) regularly taking part in a structured, supervised exercise program were enrolled in the study and evaluated for vascular function (flow-mediated dilation; FMD) and inflammatory profile (plasma CRP, IL-1ß, IL-1ra, IL-6, IL-8, IL-10, TNF-α, and MCP-1). Although no differences between groups were found concerning performance and the weekly amount of physical activity, the OW&OB group compared with the NW group demonstrated higher systolic and diastolic blood pressure (+10%, p = 0.001; +9%, p = 0.005, respectively); lower FMD% (-36%, p < 0.001) and FMD/shear rate (-40%, p = 0.001); and higher levels of CRP (+33%, p = 0.005), IL-6 (+36%, p = 0.048), MCP-1 (+17%, p = 0.004), and TNF-α (+16%, p = 0.031). No correlations between vascular function and inflammation were found in OW&OB or NW. Although exercising regularly, overweight and obese elderly exhibited poorer vascular function and higher proinflammatory markers compared with the leaner group. These results support the idea that exercise alone cannot counteract the negative effect of adiposity on vascular function and inflammatory profile in elderly individuals and these two processes are not necessarily related.