Effectiveness of an intervention to reduce sedentary behaviour as a personalised secondary prevention strategy for patients with coronary artery disease: main outcomes of the SIT LESS randomised clinical trial.

BACKGROUND: A high sedentary time is associated with increased mortality risk. Previous studies indicate that replacement of sedentary time with light- and moderate-to-vigorous physical activity attenuates the risk for adverse outcomes and improves cardiovascular risk factors. Patients with cardiovascular disease are more sedentary compared to the general population, while daily time spent sedentary remains high following contemporary cardiac rehabilitation programmes. This clinical trial investigated the effectiveness of a sedentary behaviour intervention as a personalised secondary prevention strategy (SIT LESS) on changes in sedentary time among patients with coronary artery disease participating in cardiac rehabilitation. METHODS: Patients were randomised to usual care (n = 104) or SIT LESS (n = 108). Both groups received a comprehensive 12-week centre-based cardiac rehabilitation programme with face-to-face consultations and supervised exercise sessions, whereas SIT LESS participants additionally received a 12-week, nurse-delivered, hybrid behaviour change intervention in combination with a pocket-worn activity tracker connected to a smartphone application to continuously monitor sedentary time. Primary outcome was the change in device-based sedentary time between pre- to post-rehabilitation. Changes in sedentary time characteristics (prevalence of prolonged sedentary bouts and proportion of patients with sedentary time ≥ 9.5 h/day); time spent in light-intensity and moderate-to-vigorous physical activity; step count; quality of life; competencies for self-management; and cardiovascular risk score were assessed as secondary outcomes. RESULTS: Patients (77% male) were 63 ± 10 years and primarily diagnosed with myocardial infarction (78%). Sedentary time decreased in SIT LESS (- 1.6 [- 2.1 to - 1.1] hours/day) and controls (- 1.2 [ ─1.7 to - 0.8]), but between group differences did not reach statistical significance (─0.4 [─1.0 to 0.3]) hours/day). The post-rehabilitation proportion of patients with a sedentary time above the upper limit of normal (≥ 9.5 h/day) was significantly lower in SIT LESS versus controls (48% versus 72%, baseline-adjusted odds-ratio 0.4 (0.2-0.8)). No differences were observed in the other predefined secondary outcomes. CONCLUSIONS: Among patients with coronary artery disease participating in cardiac rehabilitation, SIT LESS did not induce significantly greater reductions in sedentary time compared to controls, but delivery was feasible and a reduced odds of a sedentary time ≥ 9.5 h/day was observed. TRIAL REGISTRATION: Netherlands Trial Register: NL9263. Outcomes of the SIT LESS trial: changes in device-based sedentary time from pre-to post-cardiac rehabilitation (control group) and cardiac rehabilitation + SIT LESS (intervention group). SIT LESS reduced the odds of patients having a sedentary time >9.5 hours/day (upper limit of normal), although the absolute decrease in sedentary time did not significantly differ from controls. SIT LESS appears to be feasible, acceptable and potentially beneficial, but a larger cluster randomised trial is warranted to provide a more accurate estimate of its effects on sedentary time and clinical outcomes. CR: cardiac rehabilitation.

Sedentary Behaviour Intervention as a Personalised Secondary Prevention Strategy (SIT LESS) for patients with coronary artery disease participating in cardiac rehabilitation: rationale and design of the SIT LESS randomised clinical trial.

Patients with coronary artery disease (CAD) are more sedentary compared with the general population, but contemporary cardiac rehabilitation (CR) programmes do not specifically target sedentary behaviour (SB). We developed a 12-week, hybrid (centre-based+home-based) Sedentary behaviour IntervenTion as a personaLisEd Secondary prevention Strategy (SIT LESS). The SIT LESS programme is tailored to the needs of patients with CAD, using evidence-based behavioural change methods and an activity tracker connected to an online dashboard to enable self-monitoring and remote coaching. Following the intervention mapping principles, we first identified determinants of SB from literature to adapt theory-based methods and practical applications to target SB and then evaluated the intervention in advisory board meetings with patients and nurse specialists. This resulted in four core components of SIT LESS: (1) patient education, (2) goal setting, (3) motivational interviewing with coping planning, and (4) (tele)monitoring using a pocket-worn activity tracker connected to a smartphone application and providing vibrotactile feedback after prolonged sedentary bouts. We hypothesise that adding SIT LESS to contemporary CR will reduce SB in patients with CAD to a greater extent compared with usual care. Therefore, 212 patients with CAD will be recruited from two Dutch hospitals and randomised to CR (control) or CR+SIT LESS (intervention). Patients will be assessed prior to, immediately after and 3 months after CR. The primary comparison relates to the pre-CR versus post-CR difference in SB (objectively assessed in min/day) between the control and intervention groups. Secondary outcomes include between-group differences in SB characteristics (eg, number of sedentary bouts); change in SB 3 months after CR; changes in light-intensity and moderate-to-vigorous-intensity physical activity; quality of life; and patients' competencies for self-management. Outcomes of the SIT LESS randomised clinical trial will provide novel insight into the effectiveness of a structured, hybrid and personalised behaviour change intervention to attenuate SB in patients with CAD participating in CR. Trial registration number NL9263.

Comparison between myocardial function assessed by echocardiography during hospitalization for COVID-19 and at 4 months follow-up.

In patients hospitalized for corona virus infectious disease 19 (COVID-19) it is currently unknown whether myocardial function changes after recovery and whether this is related to elevated cardiac biomarkers. In this single center, prospective cohort study we consecutively enrolled hospitalized COVID-19 patients between 1 April and 12 May 2020. All patients underwent transthoracic echocardiography (TTE) evaluation during hospitalization and at a median of 131 days (IQR; 116-136) follow-up. Of the 51 patients included at baseline, 40 (age: 62 years (IQR; 54-68), 78% male) were available for follow-up TTE. At baseline, 68% of the patients had a normal TTE, regarding left ventricular (LV) and right ventricular (RV) volumes and function, compared to 83% at follow-up (p = 0.07). Median LV ejection fraction (60% vs. 58%, p = 0.54) and tricuspid annular plane systolic excursion (23 vs 22 mm, p = 0.18) were comparable between hospitalization and follow-up, but a significantly lower RV diameter (39 vs. 34 mm, p = 0.002) and trend towards better global longitudinal strain (GLS) (- 18.5% vs - 19.1%, p = 0.07) was found at follow-up. Subgroup analysis showed no relation between patients with and without elevated TroponinT and/or NT-proBNP during hospitalization and myocardial function at follow-up. Although there were no significant differences in individual myocardial function parameters at 4 months follow-up compared to hospitalisation for COVID-19, there was an overall trend towards normalization in myocardial function, predominantly due to a higher rate of normal GLS at follow-up.

Impact of COVID-19 lockdown on physical activity and sedentary behaviour in Dutch cardiovascular disease patients.

BACKGROUND: Coronavirus disease 2019 (COVID-19) lockdown restrictions may impact lifestyle and therefore also physical (in)activity patterns in patients with cardiovascular disease (CVD). This study aimed to evaluate the effect of lockdown on physical activity and sedentary behaviour. METHODS: A total of 1565 Dutch CVD patients participated in this prospective cohort study, in which we compared physical activity and sedentary behaviour before and during the COVID-19 lockdown period. Baseline measures were assessed in 2018 and data on follow-up measures were collected between 17 and 24 April 2020 (5 weeks after the introduction of COVID-19 lockdown restrictions). Validated questionnaires were used to assess physical activity and sedentary behaviour. RESULTS: Moderate-to-vigorous physical activities increased from 1.6 (0.9, 2.8) to 2.0 (1.0, 3.5) h/day [median (interquartile range)] (p < 0.001) during the COVID-19 lockdown, mainly due to an increase in time spent walking and doing odd jobs. In contrast, time spent exercising significantly declined [1.0 (0.0, 2.3) to 0.0 (0.0, 0.6) h/week], whereas sedentary time increased from 7.8 (6.1, 10.4) to 8.9 (6.8, 11.4) h/day (p < 0.001). The absolute increase in physical activity was 13 (-36, 81) min/day, whereas sedentary behaviour increased by 55 (-72, 186) min/day. CONCLUSION: Despite a small increase in physical activities, the larger increase in sedentary time induced a net reduction in habitual physical activity levels in Dutch CVD patients during the first-wave COVID-19 lockdown. Since a more inactive lifestyle is strongly associated with disease progression and mortality, we encourage CVD patients and their caregivers to explore novel solutions to increase physical activity levels and reduce sedentary time during (and beyond) the COVID-19 pandemic.

Higher Levels of Physical Activity Are Associated with Greater Fruit and Vegetable intake in Older Adults.

OBJECTIVE: High levels of physical activity (PA) and optimal nutrition independently improve healthy aging, but few data are available about how PA may influence food preferences in older populations. Therefore, the aim of our study was to establish if there is an association between habitual PA and intake of nutrient-dense foods (i.e. fruits and vegetables). DESIGN: A cross-sectional survey was conducted. SETTING: The Netherlands. PARTICIPANTS: 2466 older adults (56% male, age 62±9 yr). MEASUREMENTS: PA was assessed using the short questionnaire to assess health (SQUASH) and participants were classified into quintiles of weekly PA (MET-h/wk). Total fruit and vegetable intake was assessed using a validated food frequency questionnaire (FFQ) and were corrected for energy intake (g/kcal/d) in the analyses. Multiple regression analyses were performed to determine the association between PA and fruit and vegetable intake, including covariates. RESULTS: Being in the higher quintiles of PA (Q3, Q4 and Q5) was positively associated with more daily fruit and vegetable consumption, even after correction for total energy intake (Q3; ß=0.089, P<0.001, Q4; ß=0.047, P=0.024, Q5; ß=0.098, P<0.001). CONCLUSIONS: Older adults who are moderately to highly physically active tend to consume more fruit and vegetable compared to less active peers, when corrected for total energy intake. Female gender, under- and overreporting dietary intake (Goldberg score), non-smoking, high level of education, less alcohol consumption and a lower body mass index positivity affected this relationship. Our data will help health-care professionals to accelerate their efforts to treat and prevent chronic diseases.

Ionized and Total Magnesium Levels Change during Repeated Exercise in Older Adults.

BACKGROUND: Magnesium is essential for health and performance. Sub-optimal levels have been reported for older persons. In addition, physical exercise is known to temporally decrease magnesium blood concentrations. OBJECTIVE: To investigate these observations in conjunction we assessed total (tMg) and ionized magnesium (iMg) concentrations in plasma and whole blood, respectively, during 4 consecutive days of exercise in very old vital adults. DESIGN: 68 participants (age 83.7±1.9 years) were monitored on 4 consecutive days at which they walked 30-40km (average ~8 hours) per day at a self-determined pace. Blood samples were collected one or two days prior to the start of exercise (baseline) and every walking day immediately post-exercise. Samples were analysed for tMg and iMg levels. RESULTS: Baseline tMg and iMg levels were 0.85±0.07 and 0.47±0.07 mmol/L, respectively. iMg decreased after the first walking day (-0.10±0.09 mmol/L, p<.001), increased after the second (+0.11±0.07 mmol/L, p<.001), was unchanged after the third and decreased on the final walking day, all compared to the previous day. tMg was only higher after the third walking day compared to the second walking day (p=.012). In 88% of the participants, iMg levels reached values considered to be sub-optimal at day 1, in 16% of the participants values were sub-optimal for tMg at day 2. CONCLUSION: Prolonged moderate intensity exercise caused acute effects on iMg levels in a degree comparable to that after a bout of intensive exercise. These effects were not associated with drop-out or health problems. After the second consecutive day of exercise, levels were returned to baseline values, suggesting rapid adaptation/resilience in this population.

The impact of feedback during formative testing on study behaviour and performance of (bio)medical students: a randomised controlled study.

BACKGROUND: A potential concern of formative testing using web-based applications ("apps") is provision of limited feedback. Adopting a randomised controlled trial in 463 first year (bio) medical students, we explored if providing immediate, detailed feedback during "app"-based formative testing can further improve study behaviour and study performance of (bio)medical students. METHODS: Students had access to a formative testing "app", which involved 7 formative test modules throughout the 4-week course. In a randomised order, subjects received the "app" with (n = 231, intervention) or without (n = 232, control) detailed feedback during the formative test modules. RESULTS: No differences in app-use was found between groups (P = 0.15), whereas the intervention group more frequently reviewed information compared to controls (P = 0.007). Exam scores differed between non-/moderate-/intensive- users of the "app" (P < 0.001). No differences in exam scores were found between intervention (6.6 ± 1.1) versus control (6.6 ± 1.1, P = 0.18). Time spent studying was significantly higher compared to previous courses in moderate- and intensive-users (P = 0.006 and < 0.001, respectively), but not in non-users (P = 0.55). Time spent studying did not differ between groups (P > 0.05). CONCLUSIONS: Providing detailed feedback did not further enhance the effect of a web-based application of formative testing on study behaviour or study performance in (bio)medical students, possibly because of a ceiling-effect.

Determinants of vitamin D status in physically active elderly in the Netherlands.

PURPOSE: Vitamin D deficiencies are common in elderly, which increases the risk for, e.g., bone fractures. Identification of determinants of vitamin D status may provide leads for specific deficiency prevention strategies. Although determinants of vitamin D status have been studied in various populations, this has not been examined in elderly that have a physically active lifestyle. METHODS: Vitamin D status of 450 physically active elderly who do not use vitamin D supplements was determined and information on possible determinants (demographic, dietary intake and physical activity) was collected around a prolonged four day walking event in July and analyzed in linear regression models. RESULTS: The average summertime serum 25(OH)D concentration was 88.8 ± 22.4 nmol/L. Only 2% of the participants had a 25(OH)D concentration below 50 nmol/L. Dietary intake of vitamin D was 4.0 ± 1.9 µg/day, and the participants spent 12.4 ± 8.6 h/week on outdoor activities. In the multivariate model, lower age (= - 0.48, 95% CI - 0.80 to - 0.16), lower BMI (= - 0.86, 95% CI - 1.62 to - 0.10), being a moderate to high drinker versus a non-drinker (= 7.97, 95% CI 0.43-15.51) and more outdoor physical activity (= 0.25, 95% CI 0.01-0.50) were significantly associated with higher 25(OH)D concentrations. CONCLUSIONS: In physically active elderly, vitamin D status was very high in summertime, with few deficiencies, suggesting that elderly with a physical active lifestyle might not necessarily need supplements during the summer period. Lower age, lower BMI, higher alcohol intake and more outdoor physical activity had a significant association with vitamin D status.

Insufficient Protein Intakes is Highly Prevalent among Physically Active Elderly.

OBJECTIVES: Sufficient protein intake and habitual physical activity are key factors in the prevention and treatment of sarcopenia. In the present study, we assessed habitual dietary protein intake and the contribution of animal proteins in male versus female physically active elderly and identified determinants of protein intake. DESIGN: a cross-sectional study. SETTING: the study was performed within the Nijmegen Exercise Study. PARTICIPANTS: physically active elderly ≥ 65 yrs. MEASUREMENTS: Physical activity was assessed using the SQUASH questionnaire and expressed in Metabolic Equivalent of Task hours per week (METhr/wk). Dietary protein intake was determined using a validated food frequency questionnaire (FFQ). Multivariate linear regression analysis was used to determine whether age, sex, educational level, smoking, alcohol intake and physical activity were associated with protein intake (g/kg/d). RESULTS: A total of 910 participants (70±4 yrs, 70% male) were included and reported a habitual physical activity level of 85.0±53.5 METhr/wk. Protein intake was 1.1±0.3 g/kg/d with 57% animal-based proteins for males, and 1.2±0.3 g/kg/d with 59% animalbased proteins for females (both P<0.05). In total, 16%, 42% and 67% of the male elderly and 10%, 34% and 56% of the female elderly did not meet the recommended protein intake of 0.8, 1.0 and 1.2 g/kg/d, respectively. Female sex (ß=0.055, P=0.036) and more physical activity (ß=0.001, P=0.001) were associated with a higher daily protein intake (g/kg/d). CONCLUSION: The majority of physically active elderly and in particular males (i.e. 67%) does not reach a protein intake of 1.2 g/kg/d, which may offset the health benefits of an active lifestyle on muscle synthesis and prevention of sarcopenia. Intervention studies are warranted to assess whether protein supplementation may enhance muscle mass and strength in physically active elderly.

Changes in iron metabolism during prolonged repeated walking exercise in middle-aged men and women.

PURPOSE: The aim of the present study was to assess the effect of prolonged and repeated exercise on iron metabolism in middle-aged adults and to compare differences between sexes. METHODS: 50 male (58.9 ± 9.9 year) and 48 female (50.9 ± 11.2 year) individuals were monitored on 4 consecutive days at which they walked on average 8 h and 44 min per day at a self-determined pace. Blood samples were collected 1 or 2 days prior to the start of the exercise (baseline) and every day immediately post-exercise. Samples were analysed for iron, ferritin, haemoglobin, and haptoglobin concentrations. RESULTS: Plasma iron decreased across days, while ferritin increased across days (both p < 0.001). Haptoglobin showed a decrease (p < 0.001) after the first day and increased over subsequent days (p < 0.001). Haemoglobin did not change after the first day, but increased during subsequent days (p < 0.05). At baseline, 8% of the participants had iron concentrations below minimum reference value (10 µmol/L), this increased to 43% at day 4. There was an interaction between sex and exercise days on iron (p = 0.028), ferritin (p < 0.001) and haemoglobin levels (p = 0.004), but not on haptoglobin levels. CONCLUSION: This study showed decreases in iron, increases in ferritin, a decrease followed by increases in haptoglobin and no change followed by increases in haemoglobin. This is most likely explained by (foot strike) haemolysis, inflammation, and sweat and urine losses. These processes resulted in iron levels below minimum reference value in a large number of our participants.

Comparison of two telemetric intestinal temperature devices with rectal temperature during exercise.

OBJECTIVE: The discomfort caused by rectal probes and esophageal probes for the estimation of body core temperature has triggered the development of gastrointestinal (GI) capsules that are easily accepted by athletes and workers due to their non-invasive characteristics. We compare two new GI capsule devices with rectal temperature during cycle ergometer exercise and rest. APPROACH: Eight participants followed a protocol of (i) 30 min exercise with a power output of 130 W, (ii) 5 min rest, (iii) 10 min self-paced maximum exercise, and (iv) 15 min rest. Core temperature was measured using two GI-capsule devices (e-Celsius and myTemp) and rectal temperature. MAIN RESULTS: The myTemp system provided only slightly different temperatures to the rectal temperature probe during rest and exercise. However, the factory-calibrated e-Celsius system showed a systematic rectal temperature underestimation of 0.2 °C that is corrected in the 2018 versions. Both GI capsules reacted faster to temperature changes in the body compared to the rectal temperature probe during the rest period following maximum exercise. SIGNIFICANCE: The GI-capsules react faster to temperature changes in the body compared to the rectal temperature probe, in particular during the rest period following exercise.

Within-subject Variation of Thermoregulatory Responses during Repeated Exercise Bouts.

AIM: To assess the within-subject variation of thermoregulatory responses during 2 consecutive 15-km road races. Secondly, we explored whether gastrointestinal temperature (TGI) data from the first race could improve our previously established predictive model for finish TGI in the second race. METHODS: We measured TGI before and immediately after both races in 58 participants and determined correlation coefficients. Finish TGI in the second race was predicted using a linear regression analysis including age, BMI, pre-race fluid intake, TGI increase between baseline and the start of the race and finish TGI in the first race. RESULTS: Under cool conditions (WBGT 11-12°C), TGI was comparable between both races at baseline (37.6±0.4°C vs. 37.9±0.4°C; p=0.24) and finish (39.4±0.6°C vs. 39.4±0.6°C; p=0.83). Finish TGI correlated significantly between both races (r=0.50; p<0.001). The predictive model (p<0.001) could predict 32.2% of the finish TGI in the second race (vs. 17.1% without finish TGI in race 1). CONCLUSION: Our findings demonstrate that the use of previously obtained thermoregulatory responses results in higher predictability of finish core body temperatures in future races, enabling better risk assessment for those athletes that are most likely to benefit from preventive measures.

Cooling during exercise in temperate conditions: impact on performance and thermoregulation.

Exercise-induced increase in core body temperature may lead to the development of hyperthermia (>40.0°C) and/or decreased performance levels. This study examined the effects of wearing a cooling vest during a 5-km time trial on thermoregulatory responses and performance. 10 male masters athletes (42±10 years) performed a 5-km time trial on a motorized treadmill in a climate chamber (25°C, 55% relative humidity) with and without a cooling vest. Split times, heart rate, core-, skin- and cooling vest temperature were measured every 500 m. Subjects also rated thermal comfort and level of perceived exertion. The cooling vest significantly decreased heart rate (p<0.05), decreased skin temperature (p<0.001) and improved thermal comfort (p<0.005) during the time trial. Time to finish the 5-km time trial and pacing strategy did not differ between the control (1 246±96 s) and cooling vest condition (1 254±98 s, p=0.85). Additionally, thermoregulatory responses, maximum core body temperature and level of perceived exertion were not different across conditions (p=0.85, p=0.49, p=0.11, respectively). In conclusion, we demonstrated that wearing a cooling vest during exercise improves thermal comfort but does not enhance performance or decrease core body temperature in male masters athletes under temperate ambient conditions.

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.

Sex difference in fluid balance responses during prolonged exercise.

Maintaining a proper fluid balance is important during exercise as athletes are prone to develop dehydration during exercise. Although several factors may regulate the fluid balance, little is known about the role of sex during prolonged moderate-intensity exercise. Therefore, we compared body mass changes and fluid balance parameters in men vs women in a large heterogeneous group of participants during prolonged exercise. Ninety-eight volunteers walked 30-50 km at a self-selected pace. Exercise duration (8 h, 32 min) and intensity (69% HRmax) were comparable between groups. Men demonstrated a significantly larger change in body mass than women (-1.6% vs -0.9%, respectively, P < 0.001) and a higher incidence of dehydration (defined as ≥ 2% body mass loss) compared with women (34% vs 12%, respectively, odds ratio = 4.2, 95% CI = 1.1-16.7). Changes in blood sodium levels were significantly different between men (+1.5 mmol/L) and women (-0.4 mmol/L), while 27% of the men vs 0% of the women showed postexercise hypernatremia (sodium levels ≥ 145 mmol/L). Moreover, men demonstrated a significantly lower fluid intake (2.9 mL/kg/h) and higher fluid loss (5.0 mL/kg/h) compared with women (3.7 and 4.8 mL/kg/h, respectively). Taken together, our data suggest that men and women demonstrate different changes in fluid balance in response to a similar bout of exercise.

Exercise-induced cardiac troponin release: real-life clinical confusion.

Exercise training represents a successful and powerful strategy to prevent future cardiovascular disease. Paradoxically, performance of exercise is also associated with an increased risk of acute cardiac events. Accordingly, patients may present to hospital with cardiac symptoms following a bout of unaccustomed physical effort (e.g. exercise). Current guidelines for the identification of an acute myocardial infarction (AMI) importantly depend on the presence of cardiac troponin as a highly sensitive marker of cardiac damage. However, a number of studies have reported elevated cardiac troponin levels in asymptomatic, healthy subjects after endurance exercise (such as a marathon, prolonged cycling or prolonged walking). These observations indicate that elevated cardiac troponin levels can be the result of cardiac ischemia, and subsequent necrosis, but also may be related to strenuous exercise. In this paper, we present three different clinical cases of post-exercise elevations in cardiac troponins, each with a distinct clinical presentation. These case studies emphasize that a detailed assessment of all symptoms and a thorough patient-history are prerequisite for accurate interpretation of a positive cardiac troponin test following exercise.

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 (2530) 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% HR(max)) 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 risks whilst walking the Nijmegen Four Days Marches in 2007: electrolyte imbalance in 1 in 5 walkers]. / Fysieke risico's tijdens het lopen van de Nijmeegse Vierdaagse in 2007: elektrolytendisbalans bij 1 op de 5 wandelaars.

OBJECTIVE: To determine the physiological impact and health risks for walkers during the Nijmegen (the Netherlands) Four Days Marches in 2007, the largest walking event in the world with more than 45,000 participants. DESIGN: Observational study. METHODS: 66 volunteers were randomly selected and counterbalanced for distance walked and gender in this observational study. Subjects walked 30 km (n = 20; 10 men), 40 km (n = 25; 14 men) or 50 km (n = 21; 10 men) per day, for 4 consecutive days. Core body temperature, fluid intake, changes in body weight, plasma sodium concentrations and energy usage were measured before and after the marches. RESULTS: During this event, ambient temperatures ranged from 11.0 degrees C to a maximum 25.4 degrees C expressed as 'wet bulb globe temperature' (WBGT). Heart rate (+38 beats per minute) and core body temperature (+0.8 degree C) significantly increased in all subjects during each day (about 9 hours walking per day at an average of 4.6 km/h), but hyperthermia was not diagnosed (definition: > 39.0 degrees C). Average fluid intake varied between 2.6 and 3.3 l/d with a range of 0.3-12 l/d. The relative change in body weight associated with this was -3.1 to +4.3%. Mean plasma sodium concentration decreased from 142.4 to 140.6 mmol/l over each walking day. The plasma sodium correlated negatively with fluid intake (r = -0.32; p < o.001), change in body weight (r = -0.13; p < 0.05), and walking time (r = -0.37; p < 0.001). A high prevalence of hyponatraemia (5%) and hypernatraemia (16%) was observed; extrapolating these findings to the entire field a large group (about 10,000) would have been at risk with this electrolyte imbalance. CONCLUSION: This study showed that walking the Four Days Marches in Nijmegen with mild ambient conditions led to one in five participants incurring disturbances in fluid and electrolyte balance. Nonetheless, the participants were well able to keep their increasing core temperature within safe limits. Apart from the frequent electrolyte imbalance, the fluid intake varied strongly between individuals.