It has been suggested that exercise intensity is of importance in the regulation of increase in pro-inflammatory molecules, but there is still a debate about the effect of duration on these molecules. Therefore, the effect of exercise duration on the serum concentrations of interleukin-6 (IL-6), tumour necrosis factor-α (TNF-α), soluble form of intercellular adhesion molecule-1 (sICAM-1), and matrix metalloproteinase-9 (MMP-9) was studied in 22 half-marathon (HM) and 18 marathon (M) male amateur runners who completed their exercise task in 1.8 ± 0.2 (mean ± standard deviation) and 3.6 ± 0.4 h, respectively (thus, average speed was 11.7 ± 1.5 and 11.9 ± 1.8 km h(-1), respectively). Blood was sampled 2 days before, 15 min after, and 28 h after the race. IL-6, TNF-α, and MMP-9 always increased immediately after exercise, but the increase was larger (P < 0.05) in M versus HM (∆IL-6: 31 ± 24 vs. 5 ± 4 pg ml(-1); ∆TNF-α: 1.7 ± 1.9 vs. 0.5 ± 0.8 pg ml(-1); MMP-9: 288 ± 216 vs. 145 ± 128 ng ml(-1), respectively). sICAM-1 also increased with exercise, but similarly in M and HM (20 ± 40 vs. 23 ± 32 ng ml(-1), respectively). Only sICAM-1 remained elevated 28 h post-exercise in both HM and M, while IL-6, TNF-α, and MMP-9 returned to pre-exercise levels. Competitive HM and M races induce significant increases in IL-6, TNF-α, sICAM-1, and MMP-9 concentrations. As HM and M runners performed the competition with similar absolute intensity, the difference in response between the groups suggests that exercise duration is of importance in the regulation of IL-6, TNF-α, and MMP-9, but not sICAM-1 concentrations in response to prolonged running.

Interleukin-6 (IL-6) is a multifunctional cytokine that exerts its modulatory effects on cells that express membrane bound IL-6 receptors; however, IL-6 in a complex with soluble IL-6R can bind to any cell that express glycoprotein 130 (gp130). Thus, all cell types may respond to the pro- as well as anti-inflammatory properties of IL-6. Since the first report of acute exercise-induced increase in plasma IL-6 in the early 1990s, scientists have tried to elucidate the factors that influence the magnitude of change of plasma IL-6, as well as the possible biological roles of this cytokine. Evidence suggests that exercise intensity and duration as well as the form of contraction (e.g., eccentric or concentric) and muscle damage all influence IL-6 response to acute exercise. However, data on training status and performance on plasma IL-6 concentration changes during exercise are more inconclusive, as discussed in this review. In the last decade, most of the studies have focused on IL-6 as an 'energy sensor' possibly secreted by skeletal muscle that activates glycogenolysis in the liver and lipolysis in fat tissue in order to provide muscle with the growing energy demands during exercise.

The aim of this study was to test the hypothesis that exercise would induce inflammatory response characterized by increased pro‐inflammatory cytokines – interleukin‐6 (IL‐6) and tumour necrosis factor‐α (TNF‐α), adhesion molecule, matrix metalloprotease‐9 (MMP‐9) and myeloperoxidase (MPO) levels. Additional aim was to elucidate the possible source of maximal exercise‐induced increase in MMP‐9 concentration. To examine our hypothesis, 26 professional male ice hockey players [age 25 ± 1 (mean ± SEM) years; BMI 25.8 ± 0.4 kg/m2] performed an incremental bicycle test until exhaustion, when maximal oxygen consumption was recorded. Venous blood samples were collected 30 min before and 2 min after exercise. There was an increase in the count of leucocytes (8.7 ± 1.8 versus 5.7 ± 1.3 × 109 cells per l) and IL‐6 (1.24 ± 0.17 versus 0.69 ± 0.13 pg/ml), MPO (72 ± 7 versus 50 ± 4 ng/ml) and MPP‐9 (139 ± 9 versus 110 ± 6 ng/ml) concentrations (P < 0.05) comparing post‐ and pre‐exercise levels. Maximal exercise‐induced increase in MPO correlated with the increases in IL‐6 (P < 0.05, R = 0.54) and MMP‐9 (P < 0.01, R = 0.62) concentrations. Furthermore, increase in IL‐6 correlated with the increase in MMP‐9 concentrations (P < 0.05, R = 0.60). Maximal exercise induces an inflammatory response characterized by leucocytosis and increased IL‐6, MPO and MMP‐9 concentrations. Correlations between increased MPO (marker of neutrophils degranulation) and both increased IL‐6 and MMP‐9 concentrations may suggest that neutrophils could be the main source of these inflammatory biomarkers during maximal exercise. Furthermore, correlation between increases in serum IL‐6 and MMP‐9 concentrations may suggest that IL‐6 could exert modulatory effects on MMP‐9 release during maximal exercise.

New Findings r What is the central question of this study?Does physical inactivity influence the exercise-induced release of tumour necrosis factor-α and interleukin-6 in healthy humans? In young, healthy subjects, we immobilized one leg for 2 weeks, followed by 45 min two-legged exercise where one leg served as the control and the other was the previously inactive leg. r What is the main finding and its importance?We found that prior physical inactivity enhances interleukin-6 release during exercise, and it is released in the blood from the legs during exercise much faster than previously known. However, tumour necrosis factor-α is not released in the blood with exercise, even from a previously inactive leg.Data on interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α) release during acute exercise are not conclusive, and information is lacking about the impact of physical inactivity. Some studies have shown an increase, but others report no changes in IL-6 and TNF-α release during exercise. We have now studied the temporal relationship of leg IL-6 and TNF-α release before and during isolated two-legged exercise after 14 days of one-leg immobilization (IM) while the other leg served as the control (CON) leg. Fifteen healthy male subjects (mean ± SEM age, 23 ± 1 years; body mass index, 23.6 ± 0.7 kg m −2 ; and maximal oxygen uptake, 46.8 ± 1.4 ml kg −1 min −1 ) performed 45 min of two-legged dynamic knee-extensor exercise at 19.6 ± 0.8 W. Arterial and femoral venous blood samples from the CON and the IM leg were collected every 15 min during exercise, and leg blood flow was measured with Doppler ultrasound. The arterial plasma IL-6 concentration increased (P < 0.05) with exercise (rest, 1.3 ± 0.1 pg ml −1 ; 15 min, 1.9 ± 0.2 pg ml −1 ; 30 min, 2.4 ± 0.2 pg ml −1 ; and 45 min, 3.1 ± 0.3 pg ml −1 ). Interleukin-6 release occurred after 15 min of exercise, and the release from the IM leg was significantly greater compared with the CON leg after 45 min (1114 ± 152 versus 606 ± 14 pg min −1 , respectively, P < 0.05). Tumour necrosis factor-α release did not differ between the CON and the IM leg, and arterial concentrations remained unchanged during exercise (P > 0.05). In conclusion, prior immobilization enhances release of IL-6 from the leg during exercise at a moderate workload, and the release is already present in the early phase of exercise. Neither immobilization nor exercise had an effect on TNF-α release in the working legs.

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Physical inactivity is a major contributor to low-grade systemic inflammation. Most of the studies characterizing interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α) release from exercising legs have been done in young, healthy men, but studies on inactivity in older people are lacking. The impact of 14 days of one-leg immobilization (IM) on IL-6 and TNF-α release during exercise in comparison to the contralateral control (CON) leg was investigated. Fifteen healthy men (age 68.1 ± 1.1 year (mean ± SEM); BMI 27.0 ± 0.4 kg·m(2); VO2max 33.3 ± 1.6 ml·kg(‒1)·min(‒1)) performed 45 min of two-leg dynamic knee extensor exercise at 19.5 ± 0.9 W. Arterial and femoral venous blood samples from the CON and the IM legs were collected every 15 min during exercise, and thigh blood flow was measured with ultrasound Doppler. Arterial plasma IL-6 concentration increased with exercise (rest vs. 45 min, main effect p < .05). IL-6 release increased with exercise (rest vs. 30 min, main effect p < .05). Furthermore, IL-6 release was borderline (main effect, p = .085, effect size 0.28) higher in the IM leg compared to the CON leg (288 (95% CI: 213-373) vs. 220 (95% CI: 152-299) pg·min(‒1), respectively). There was no release of TNF-α in either leg and arterial concentrations remained unchanged during exercise (p > .05). In conclusion, exercise induces more pronounced IL-6 secretion in healthy older men. Two weeks of unilateral immobilization on the other hand had only a minor influence on IL-6 release. Neither immobilization nor exercise had an effect on TNF-α release across the working legs in older men.

Growing incidence of obesity and related diseases in children poses new challenges and calls for a review of lifestyle habits. This study aimed to assess daily eating habits (EH) and physical activity (PA) levels and identify their association with obesity in 8–10-year-old children. Children’s EH and time spent in moderate-to-vigorous physical intensity (MVPA) was estimated from questionnaires (N = 1788). Weight, height, and waist circumference (WC) were collected, and body mass index (BMI) calculated. Girls consumed more fruits and vegetables, drank more water, and ate smaller portions of carbohydrate and protein rich foods but spent less time in MVPA compared to boys (p < 0.05). Obese children skipped breakfast more often and consumed less fruits and vegetables. Children who chose to eat in front of the screen had higher WC (62.88 ± 8.70 vs 60.59 ± 7.40 cm, p < 0.001) and higher BMI, and chose smaller vegetable portions and more calorie dense snacks (p < 0.001). 15.4% of pupils covered weekly MVPA recommendations with structured PA on weekdays. Increasing MVPA was related to a smaller number of unhealthy EH (p < 0.001). In conclusion, EH and PA levels differ between sexes and obese children have unhealthier EH. Higher levels of MVPA are related to healthier food choices, while pupils having meals in front of the screen have unhealthier EH and anthropometric measures. The majority of pupils did not reach the WHO recommendations of MVPA through structured PA on weekdays. Association between factors (EH and time spent in PA) and BMI was not found in this study.