Fleur Poelkens

Impact of physical fitness and daily energy expenditure on sleep efficiency in young and older humans

Background: Physical activity is known to influence sleep efficiency. Relatively little is known about the relationship between physical activity and sleep efficiency in young and older humans and the impact of exercise training on sleep efficiency in healthy older individuals. Objectives: To determine the relationship between physical fitness and daily energy expenditure with sleep efficiency in young and older subjects, and assess the effect of 12-month exercise training on sleep efficiency in healthy older participants. Methods: The relationship between physical fitness (maximal cycling test) and daily energy expenditure (accelerometry) with sleep efficiency (accelerometry) was examined cross-sectionally in 12 healthy young adults (27 ± 5 years) and 21 healthy older participants (69 ± 3 years). Subsequently, the effect of 12-month exercise training (n = 11) or control period (n = 10) on sleep efficiency in older participants was examined using a randomized controlled trial. Results: Daily energy expenditure and sleep efficiency did not differ between young and older subjects. A significant correlation was found between energy expenditure and sleep efficiency (r = 0.627, p = 0.029) in young adults, but not in older participants (r = –0.158, p = 0.49). Physical fitness did not correlate with sleep efficiency in either group. Exercise training significantly improved physical fitness (15.0%, p < 0.001), but failed to alter sleep characteristics such as sleep efficiency, sleep onset latency and awakenings. Conclusions: We found that young adults with higher daily energy expenditure have greater sleep efficiency, whilst this relationship is diminished with advanced age. In contrast, we found no correlation between physical fitness and sleep characteristics in healthy young or older participants, which may explain the lack of improvement in sleep characteristics in older participants with 12-month exercise training. Exercise training may be more successful in subjects with existing sleep disturbances to improve sleep characteristics rather than in healthy older subjects.

Leg intravenous pressure during head-up tilt

Leg vascular resistance is calculated as the arterial-venous pressure gradient divided by blood flow. During orthostatic challenges it is assumed that the hydrostatic pressure contributes equally to leg arterial, as well as to leg venous pressure. Because of venous valves, one may question whether, during orthostatic challenges, a continuous hydrostatic column is formed and if leg venous pressure is equal to the hydrostatic pressure. The purpose of this study was, therefore, to measure intravenous pressure in the great saphenous vein of 12 healthy individuals during 30 degrees and 70 degrees head-up tilt and compare this with the calculated hydrostatic pressure. The height difference between the heart and the right medial malleolus level represented the hydrostatic column. The results demonstrate that there were no differences between the measured intravenous pressure and the calculated hydrostatic pressure during 30 degrees (47.2 +/- 1.0 and 46.9 +/- 1.5 mmHg, respectively) and 70 degrees head-up tilt (83.9 +/- 0.9 and 85.1 +/- 1.2 mmHg, respectively). Steady-state levels of intravenous pressure were reached after 95 +/- 12 s during 30 degrees and 161 +/- 15 s during 70 degrees head-up tilt. In conclusion, the measured leg venous pressure is similar to the calculated hydrostatic pressure during orthostatic challenges. Therefore, the assumption that hydrostatic pressure contributes equally to leg arterial as well as to leg venous pressure during orthostatic challenges can be made.

Counteracting venous stasis during acute lower leg immobilization

Aim:  During lower limb immobilization, patients are at risk to develop deep venous thrombosis. Recently, a water‐pad was developed that should counteract venous stasis. The water‐pad, located under the plaster, mobilizes water from the foot to the calf during weight bearing and, thereby, imitates muscle pump function. The purpose of this study was to assess the effect of the water‐pad on venous pump function in healthy individuals.

The impact of obesity on physiological responses during prolonged exercise

Background:Prolonged, moderate-intensity exercise training is routinely prescribed to subjects with obesity. In the general population, this type of exercise can lead to fluid and sodium imbalance. However, little is known whether obesity alters the risk of fluid and sodium imbalances.Objective:This study examined physiological responses, such as core body temperature, fluid and sodium balance, in lean (BMI<25), overweight (25<BMI<30) and obese (BMI>30) subjects during prolonged moderate-intensity exercise.Subjects:A total of 93 volunteers (24–80 years), stratified for BMI, participated in the Nijmegen Marches and walked 30–50 km at a self-selected pace. Heart rate and core body temperature were recorded every 5 km. Subjects reported fluid intake, while urine output was measured and sweat rate was calculated. Baseline and post-exercise plasma sodium levels were determined, and urinary specific gravity levels were assessed before and after exercise.Results:BMI groups did not differ in training status preceding the experiment. Exercise duration (8 h 41±1 h 36 min) and intensity (72±9% HRmax) were comparable across groups, whereas obese subjects tended to have a higher maximum core body temperature than lean controls (P=0.06). Obese subjects demonstrated a significantly higher fluid intake (P<0.001) and sweat rate (P<0.001), but lower urine output (P<0.05) compared with lean subjects. In addition, higher urine specific gravity levels were observed in obese versus lean subjects after exercise (P<0.05). Furthermore, plasma-sodium concentration did not change in lean subjects after exercise, whereas plasma-sodium levels increased significantly (P<0.001) in overweight and obese subjects. Also, overweight and obese subjects demonstrated a significantly larger decrease in body mass after exercise than lean controls (P<0.05).Conclusion:Obese subjects demonstrate a larger deviation in markers of fluid and sodium balance than their lean counterparts during prolonged moderate-intensity exercise. These findings suggest that overweight and obese subjects, especially under strenuous environmental conditions, have an increased risk to develop fluid and sodium imbalances.

Physical Fitness can Partly Explain the Metabolically Healthy Obese Phenotype in Women

To investigate whether physical fitness and/or fat distribution and inflammation profile may explain why approximately 30% of the women with obesity are protected against obesity-related disorders.10 metabolically healthy obese women and 10 age- and weight-matched women with the metabolic syndrome were enrolled. Physical fitness (VO2max), daily physical activity levels (METs, steps per day), insulin sensitivity (clamp), body fat distribution (DXA scan) and, inflammation markers and adipokines were determined.The metabolically healthy obese women had a 17% higher VO2max (25.1±3.9 vs. 21.5±3.1 ml ∙ min-1 ∙ kg-1, p=0.04) and tended to take more steps per day (7 388±1 440 vs. 5 927±1 301, p=0.06) than women with the metabolic syndrome. Despite equivalent levels of fat mass, metabolically healthy obese women had significantly lower circulating TNF-α levels compared to women with the metabolic syndrome (3.55±3.83 vs. 0.43±0.97 ng/ml, p=0.03). No differences were seen in insulin sensitivity, adipokines, and inflammatory markers between both groups.Metabolically healthy obese women have a higher cardio-respiratory fitness and lower TNF-α levels, which may partly explain why these women are protected from the detrimental effects of obesity compared to obese women with the metabolic syndrome.

Upregulation of skeletal muscle inflammatory genes links inflammation with insulin resistance in women with the metabolic syndrome

•  What is the central question of this study? There is a close relationship between insulin resistance and inflammation, but it is largely unknown how these processes are linked in skeletal muscle tissue. •  What is the main finding and its importance? Gene expression microarray analysis identified three inflammatory genes the expression level of which was highly correlated with insulin resistance in women with the metabolic syndrome. This suggests an important role for these genes in the development of skeletal muscle insulin resistance.

Letter by Poelkens et al Regarding Article, “Aerobic Interval Training Versus Continuous Moderate Exercise as a Treatment for the Metabolic Syndrome: A Pilot Study”

To the Editor: We read with great interest the article by Tjonna et al1 that addressed the efficacy of different modes of exercise training to reverse features of the metabolic syndrome. The metabolic syndrome, considered an ailment of the 20th century, consists of a clustering of risk factors, with insulin resistance still viewed as the common pathophysiological pathway.2 We …

Improvements in fitness are not obligatory for exercise training-induced improvements in CV risk factors

The purpose of this study was to assess whether changes in physical fitness relate to changes in cardiovascular risk factors following standardized, center‐based and supervised exercise training programs in subjects with increased cardiovascular risk. We pooled data from exercise training studies of subjects with increased cardiovascular risk (n = 166) who underwent 8–52 weeks endurance training. We determined fitness (i.e., peak oxygen uptake) and traditional cardiovascular risk factors (body mass index, blood pressure, total cholesterol, high‐density lipoprotein cholesterol), before and after training. We divided subjects into quartiles based on improvement in fitness, and examined whether these groups differed in terms of risk factors. Associations between changes in fitness and in cardiovascular risk factors were further tested using Pearson correlations. Significant heterogeneity was apparent in the improvement of fitness and individual risk factors, with nonresponder rates of 17% for fitness, 44% for body mass index, 33% for mean arterial pressure, 49% for total cholesterol, and 49% for high‐density lipoprotein cholesterol. Neither the number, nor the magnitude, of change in cardiovascular risk factors differed significantly between quartiles of fitness change. Changes in fitness were not correlated with changes in cardiovascular risk factors (all P > 0.05). Our data suggest that significant heterogeneity exists in changes in peak oxygen uptake after training, while improvement in fitness did not relate to improvement in cardiovascular risk factors. In subjects with increased cardiovascular risk, improvements in fitness are not obligatory for training‐induced improvements in cardiovascular risk factors.

Exercise Improves Insulin Sensitivity in the Absence of Changes in Cytokines.

PURPOSE The benefits of aerobic exercise training on insulin sensitivity in subjects with metabolic syndrome (MetS) are, at least in part, associated with changes in cytokines. Recent studies identified novel cytokines (e.g., fractalkine, omentin, and osteopontin) that are strongly involved in glucose homeostasis and therefore potentially contribute in the exercise-induced changes in insulin sensitivity. Therefore, we aim to examine changes in skeletal muscle RNA expression and plasma levels of novel cytokines after exercise training and correlate these changes to the exercise-induced changes in insulin sensitivity. METHODS Women with metabolic syndrome (MetS, n = 11) and healthy women (n = 10) participated in a 6-month aerobic exercise training intervention (three times a week, 45 min per session at 65%-85% of individual heart rate reserve). Before and after training, we examined insulin sensitivity (M value during hyperinsulinemic euglycemic clamp) and circulating blood levels of cytokines (venous blood sample; leptin, adiponectin, omentin, fraktalkin, and osteopontin). The skeletal muscle RNA expression of these cytokines (muscle biopsy) was examined in two subgroups (MetS, n = 6; healthy women, n = 6). RESULTS At baseline, plasma levels of omentin (85.8 ± 26.2 ng·mL) and adiponectin (5.0 ± 1.7 μg·mL) levels were significantly higher in controls compared with MetS (51.1 ± 27.1; 3.6 ± 1.1 respectively), and leptin levels were lower in controls (18.7 ± 11.5 vs 53.0 ± 23.5 ng·mL). M value was significantly higher in controls (8.1 ± 1.9 mg·kg·min) than in MetS (4.0 ± 1.7). Exercise training significantly improved M values in both groups (P < 0.01). Exercise training did not alter plasma and skeletal muscle RNA expression levels of cytokines, but no correlation was observed between changes in cytokine level/RNA expression and M values (P > 0.05). CONCLUSION Although exercise training successfully improves insulin sensitivity in MetS and healthy women, we found no change in plasma and mRNA expression levels of novel cytokines.

Fysieke inactiviteit en training beïnvloeden de expressie van genen betrokken bij vetzuurtransport en insulinesignaaltransductie in skeletspier bij mensen

SamenvattingFysieke inactiviteit is geassocieerd met het ontstaan van chronische aandoeningen, zoals type 2 diabetes mellitus en cardiovasculaire ziekten. Regelmatig bewegen is een effectieve manier om deze nadelige gevolgen tegen te gaan, maar de onderliggende mechanismen zijn grotendeels onbekend. Om meer inzicht in deze mechanismen te krijgen, hebben wij met behulp van genexpressie-microarrays het expressieniveau van alle bekende genen in de spier bepaald bij mensen, na fysieke deconditionering versus training van de benen.