How much physical activity is optimal for health? Methodological considerations

Exercise and Experiments of Nature

In this article, we highlight the contributions of passive experiments that address important exercise-related questions in integrative physiology and medicine. Passive experiments differ from active experiments in that passive experiments involve limited or no active intervention to generate observations and test hypotheses. Experiments of nature and natural experiments are two types of passive experiments. Experiments of nature include research participants with rare genetic or acquired conditions that facilitate exploration of specific physiological mechanisms. In this way, experiments of nature are parallel to classical "knockout" animal models among human research participants. Natural experiments are gleaned from data sets that allow population-based questions to be addressed. An advantage of both types of passive experiments is that more extreme and/or prolonged exposures to physiological and behavioral stimuli are possible in humans. In this article, we discuss a number of key passive experiments that have generated foundational medical knowledge or mechanistic physiological insights related to exercise. Both natural experiments and experiments of nature will be essential to generate and test hypotheses about the limits of human adaptability to stressors like exercise. © 2023 American Physiological Society. Compr Physiol 13:4879-4907, 2023.

Impact of a Progressive Mobility Program on the Functional Status, Respiratory, and Muscular Systems of ICU Patients: A Randomized and Controlled Trial

OBJECTIVES

The aim was to investigate whether patients who participated in a mobility program in the ICU performed better on functional status, muscle, mobility, and respiratory assessments upon discharge than patients who received conventional physiotherapy.

DESIGN

Randomized controlled trial.

SETTING

Blind evaluation.

PATIENTS

Adults with previous functional independence and without contraindications for mobilization were eligible.

INTERVENTIONS

The intervention group participated in an early and progressive mobility program with five levels of activity. The control group underwent the conventional treatment without a preestablished routine. We evaluated functional status, level of activity, respiratory status, muscle strength, and mobility at ICU discharge.

MEASUREMENTS AND MAIN RESULTS

We analyzed 49 patients in the control group and 50 patients in the intervention group. Our data showed patients with better functional status and more functionally independent patients in the intervention group compared with those in the control group (96% vs 44%; p < 0.001). The results of the sit-to-stand and 2-minute walk tests, as well as the results of the maximum voluntary ventilation tests, also varied between the groups. The intervention group had shorter ICU stays than the control group. Higher Barthel index scores were associated with the amount of activity and participation in the protocol. The benefits to functional status remained during follow-up.

CONCLUSIONS

Patients who participated in an ICU mobility program had better functional status at discharge from the ICU. The other benefits of the program included better performance in the mobility tests and improved maximum voluntary ventilation performance.

C-reactive protein mediates the association between leisure-time physical activity and lung function in middle-aged and older adults

Background

Although previous studies have reported the benefits of physical activity (PA) to lung function in middle-aged and older adults, the biological mechanisms are still unclear. This study aimed to assess the extent to which C-reactive protein (CRP) mediates the association between leisure-time PA and lung function.

Methods

A population-based sample was recruited from English Longitudinal Study of Ageing (ELSA), Wave 6 (2012–2013). PA was self-reported by questionnaires. CRP was analyzed from peripheral blood. Lung function parameters including forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) were measured by using a spirometer. Baron and Kenny’s causal steps method and multiple linear regression models based on the Karlson/Holm/Bree (KHB) method were used to assess the mediating effect.

Results

Among 6875 participants, 28.4% were classified into low PA, 49.8% into moderate PA, and 21.8% into high PA. Multiple linear regression models suggested that higher PA was associated with lower levels of CRP (β = − 0.048, P = 0.002 for moderate PA; β = − 0.108, P < 0.001 for high PA). CRP negatively correlated with FEV1 (β = − 0.180, P < 0.001) and FVC (β = − 0.181, P < 0.001). Higher levels of PA were associated with better FEV1 (β = 0.085, P < 0.001 for moderate PA; β = 0.150, P < 0.001 for high PA) and FVC (β = 0.131, P < 0.001 for moderate PA; β = 0.211, P < 0.001 for high PA). After introducing the CRP into the models, regression coefficients of PA with FEV1 (β = 0.077, P < 0.001 for moderated PA; β = 0.130, P < 0.001 for high PA) and FVC (β = 0.123, P < 0.001 for moderated PA; β = 0.188, P < 0.001 for high PA) decreased. The indirect effect of high PA on lung function via CRP was significant, with 9.42–12.99% of the total effect being mediated.

Conclusions

The association between PA and lung function is mediated by CRP, suggesting that this association may be partially explained by an inflammation-related biological mechanism. This finding highlights the possible importance of PA in systemic inflammation and lung function, thus, middle-aged and older adults should be encouraged to enhance PA levels.

The association between leisure-time physical activity and lung function in older adults: The English longitudinal study of ageing

The longitudinal association between physical activity and lung function is unclear. Therefore, we examined said association over eight years. This study included data from 2966 participants in English Longitudinal Study of Ageing (63±7years [mean±SD]), a prospective study of initially healthy, community dwelling adults. Physical activity was assessed using an interview and lung function using a spirometer at baseline (2004-5) and follow-up (2012-13). General linear regression was used to assess associations between activity and lung function. Logistic regression was used to assess the odds of new cases of abnormal lung function. Some 14% of participants were defined as physically inactive at baseline, 50% were classified into the moderate group, and 36% into the vigorous group. In comparison with remaining inactive at follow-up, remaining active was positively associated with forced vital capacity (FVC) (β=0.09, 95% confidence interval [CI]: 0.01, 0.17; p=0.02) and forced expiratory volume in one second (FEV-1) (β=0.09, 95% CI: 0.02, 0.15; p=0.01) after adjustment for baseline lung function score and other covariates. Using the fifth centile to define the lower limit of normal (that is, -1.64 z scores), there were lower odds of incident abnormal lung function in participants who remained physically active compared to those who remained inactive (FVC odds ratio=0.31, 95% CI: 0.17, 0.55. FEV-1 odds ratio=0.43, 95% CI: 0.26, 0.72). Similar associations were observed in those who became active. This study suggests that remaining physically active or becoming active in older age is positively associated with lung function and reduced odds of abnormal lung function.

Predictors of functional shoulder recovery at 1 and 12 months after breast cancer surgery

The objective of this study are (1) to determine if upper extremity function, as represented by shoulder ROM, self-reported symptoms and upper extremity functional limitations in activities of daily living could be predictively related to demographic and cancer characteristics post-surgery for breast cancer. And (2) to examine if variables related to early onset impairment contribute to late onset impairments in women after breast cancer surgery. Subjects were assessed preoperatively and 1, 3, 6, 9, and 12+ months post breast cancer surgery for impairments and symptoms and at 12+ months for shoulder functional limitations using a physical therapy surveillance model. Body weight, shoulder ROM, manual muscle testing, and upper limb volume were recorded. At 12+ months, the Harvard Alumni Health Study Physical Activity Questionnaire, and an Upper Limb Disability Questionnaire were administered. Symptoms and ROM impairments were compared by functional limitations. Characteristics significantly associated with early ROM impairment (but not later impairment) were axillary lymph node dissection, removal of ≥15 nodes, mastectomy surgery and stage II breast cancer. Positive nodes, older age, and BMI≥25 were significantly associated with reduced shoulder ROM at 12+ months. At 12+ months, only 10 % of the patients experienced ROM impairments while rates of self-reported symptoms in the affected upper extremity at 12+ months were as follows: pain-49%, weakness-47.1%, numbness-55.9%, feeling tired-42.5%. The majority of patients used the affected upper extremity for reaching without limitation, but ≥35% reported limitation with household chores, carrying and lifting. Difficulty carrying and lifting could be predicted by BMI≥25 and use of the dominant affected upper limb. Different factors are associated with early versus later ROM loss. Symptoms reported by breast cancer survivors are frequently associated with functional limitations in upper extremity tasks and warrant intervention. Physical therapy using a prospective surveillance model of care may reduce severity of ROM loss, symptoms and functional upper extremity limitations 1 year after breast cancer surgery.

Prevalence and risk factors of urinary incontinence in Chinese women: a population-based study

To estimate the current prevalence rate of urinary incontinence (UI) and to identify risk factors in Chinese women, we conducted a population-based survey in 3058 women in Beijing, China, in 2009. The prevalence rate of UI was estimated to be 22.1%, with stress UI (12.9%) being more prevalent than urgency UI (1.7%) and mixed UI (7.5%). The prevalence rates of UI, urgency UI, and mixed UI increased with age, with the highest recorded in participants aged ≥70 years. However, stress UI was most commonly seen in participants aged 50 to 69 years. Risk factors for UI included aging, lower education background, older age of menarche, menstrual disorder, pregnancy history, episiotomy, chronic pelvic pain, gynecological disease, other chronic diseases, constipation, fecal incontinence, lower daily water intake, and frequency of high protein intake. UI is a common disorder in Chinese women, and many risk factors are able to affect the development of UI.

The ABC of Physical Activity for Health: a consensus statement from the British Association of Sport and Exercise Sciences

Our understanding of the relationship between physical activity and health is constantly evolving. Therefore, the British Association of Sport and Exercise Sciences convened a panel of experts to review the literature and produce guidelines that health professionals might use. In the ABC of Physical Activity for Health, A is for All healthy adults, B is for Beginners, and C is for Conditioned individuals. All healthy adults aged 18-65 years should aim to take part in at least 150 min of moderate-intensity aerobic activity each week, or at least 75 min of vigorous-intensity aerobic activity per week, or equivalent combinations of moderate- and vigorous-intensity activities. Moderate-intensity activities are those in which heart rate and breathing are raised, but it is possible to speak comfortably. Vigorous-intensity activities are those in which heart rate is higher, breathing is heavier, and conversation is harder. Aerobic activities should be undertaken in bouts of at least 10 min and, ideally, should be performed on five or more days a week. All healthy adults should also perform muscle-strengthening activities on two or more days a week. Weight training, circuit classes, yoga, and other muscle-strengthening activities offer additional health benefits and may help older adults to maintain physical independence. Beginners should work steadily towards meeting the physical activity levels recommended for all healthy adults. Even small increases in activity will bring some health benefits in the early stages and it is important to set achievable goals that provide success, build confidence, and increase motivation. For example, a beginner might be asked to walk an extra 10 min every other day for several weeks to slowly reach the recommended levels of activity for all healthy adults. It is also critical that beginners find activities they enjoy and gain support in becoming more active from family and friends. Conditioned individuals who have met the physical activity levels recommended for all healthy adults for at least 6 months may obtain additional health benefits by engaging in 300 min or more of moderate-intensity aerobic activity per week, or 150 min or more of vigorous-intensity aerobic activity each week, or equivalent combinations of moderate- and vigorous-intensity aerobic activities. Adults who find it difficult to maintain a normal weight and adults with increased risk of cardiovascular disease or type 2 diabetes may in particular benefit from going beyond the levels of activity recommended for all healthy adults and gradually progressing towards meeting the recommendations for conditioned individuals. Physical activity is beneficial to health with or without weight loss, but adults who find it difficult to maintain a normal weight should probably be encouraged to reduce energy intake and minimize time spent in sedentary behaviours to prevent further weight gain. Children and young people aged 5-16 years should accumulate at least 60 min of moderate-to-vigorous-intensity aerobic activity per day, including vigorous-intensity aerobic activities that improve bone density and muscle strength.

Nível de atividade física como estimador da aptidão física de estudantes universitários: explorando a adoção de questionário através de modelagem linear

A classificação do nível de atividade física (NAF) tem-se revelado aspecto controvertido em Ciência do Esporte. Nesta perspectiva, o objetivo da presente investigação foi verificar a utilização de instrumento adaptado para classificação do NAF. Para tanto, foi desenvolvido estudo transversal seriado, considerando NAF como variável independente e a aptidão física como dependente. Identificaram-se como população de estudo calouros do curso de Medicina, em total de 290 pessoas. Foram coletados durante três anos subseqüentes, através de anamnese dirigida, informações a respeito do NAF e testes de capacidade aeróbia e muscular, para conhecer as variáveis de aptidão física (AF). A análise estatística foi realizada através do modelo Linear, sendo aplicado o teste F para avaliar o efeito das variáveis independentes, bem como a prova de Tukey para comparar as respectivas médias e o modelo de Poisson para verificar o efeito das variáveis dependentes, segundo nível de atividade física e sexo. Como principal resultado, destaca-se o fato de as pessoas que referiram maior NAF também apresentaram os melhores escores de AF indicando que a utilização do instrumento revelou-se coerente e compatível.

Physical activity of moderate intensity in leisure time and the risk of all cause mortality

BACKGROUND

There are conflicting data about the health benefits of moderately intense physical activity.

OBJECTIVES

To examine the effect of such activity on all cause mortality in a German sample of men and women.

METHODS

Physical activity during leisure time of 3742 men and 3445 women aged 30 to 69 was assessed in a baseline questionnaire from 1984 to 1986. The participants were observed during the follow up period until 1998 when a mortality follow up was conducted.

RESULTS

During the follow up period, 300 women and 643 men had died. The multivariate rate ratios (RR) for the volume of lifestyle activities of moderate intensity (for example, gardening, walking, cycling) compared with sedentary lifestyle showed a clearly protective dose-response relation (p for trend <0.001) in women but not in men (p for trend 0.20). Following the recommendation for health enhancing physical activity a second analysis was conducted; 2.5 hours per week taking part in physical activity of moderate intensity decreased the relative risk of overall mortality (0.65 (95% confidence interval, 0.51 to 0.82) and 0.90 (0.77 to 1.01) for women and men, respectively).

CONCLUSIONS

The volume of lifestyle activities of moderate intensity in leisure time was inversely associated with all cause mortality in women but not in men. With regard to the health enhancing physical activity recommendation as a threshold, there were favourable findings only in women.

Health and physical activity research as represented in RQES

In the past 75 years, articles in Research Quarterly for Exercise and Sport (RQES) have contributed to the understanding of the role physical activity plays in the health of individuals and populations. Articles have described laboratory and community research studies in humans and animals, presented reviews of topics and conference proceedings, and presented forums for discussion about current topics in physical activity and health. The articles reflect the growth of the profession from basic inquiry, about physiological responses to exercise (and the development of physical fitness methods and standards), to studies of the effects of exercise on physical fitness and health in various population subgroups. This evolution in RQES reflects the well recognized paradigm shift toward public health concerns for physical activity and health outcomes.

Accumulating aerobic exercise for effective weight control

PURPOSE

To compare the effects of different patterns of regular treadmill walking and cycle ergometry on body weight, body composition, waist and hip circumferences in overweight adult Singaporean females.

METHODS

Thirty overweight (BMI > 23 kg/m2) Singaporean females, aged 42.2 +/- 5.4 yr (mean +/- SD), all spasmodically physically active, were randomly assigned to two different eight-week programmes of aerobic exercise. One programme involved walking and cycling on indoor exercise machines at a moderate, comfortable intensity until 400 kcals had been expended, five times a week, thus giving a total weekly energy expenditure of 2,000 kcal. The other programme involved the same type of exercise but expending 1,000 kcal per session on two days a week, thereby giving the same weekly energy expenditure. Body weight, body mass index, body composition, waist and hip circumferences were measured before and after each programme. Prior to commencement of the study all subjects attended a one hour seminar on nutrition, health and fitness where the project structure was explained. They were asked not to change their eating habits during the intervention period and food diaries were kept and monitored weekly.

RESULTS

All subjects completed the eight-week programmes of exercise. Both programmes significantly reduced body weight, body mass index, percentage body fat and waist circumference (all p < 0.05). These reductions were identical in both the short-bout and long-bout programmes. No changes were observed in either group for hip circumference or lean body mass.

CONCLUSION

These findings demonstrated the effectiveness of moderate aerobic exercise in reducing body weight, body fat percentage and waist circumference whilst maintaining lean body mass in moderately overweight Singaporean females. The study also demonstrated that whether the exercise is performed in a series of short bouts five times a week or in longer bouts twice a week, the results are identical, providing that the total weekly energy expenditure remains the same.

Reported frequency of physical activity, fitness, and fatness in Kuwait

We studied reported frequency of physical activity (PA), body composition, and fitness in Kuwaiti females (n = 84) and males (n = 72), urban office government employees, or students. A sedentary (SED) group reported no or occasional participation in self-directed PA of 30 minutes or more during the week for the last 6 months; group LOF (low frequency) participated in 1-2 sessions/week (walking, jogging, sports such as volleyball, soccer, or gym); group HIF (higher frequency) reported three or more sessions/week. Aerobic fitness was measured using Bruce's treadmill protocol. Body fat and fat-free mass (FFM) were estimated from seven skinfolds and body weight (BW). Grip strength and trunk flexibility were also measured. Maximal O(2) consumption (VO(2)max)/BW was proportional to reported frequency of PA in males and females, indicating reliability of the reported PA frequencies. SED males (%fat > 25), SED and LOF females (%fat > 30) were overweight. In males, LOF PA was associated with lower %fat and higher flexibility than SED, and in females with higher VO(2)max/FFM than SED. LOF females, in contrast to males, were resilient to or exercised at levels insufficient for fat loss but sufficient for aerobic conditioning of the FFM, likely related to the low VO(2)max of females in which PA would have the most effect. HIF PA (>/=3/week) was associated in females with significantly lower %fat and higher flexibility than SED females and no further aerobic conditioning of the FFM, and in males with no further differences in study variables compared with LOF males. Grip strength was higher in males than females but was unrelated to frequency of PA, likely reflecting lack of strength training in the activities of most participants. Thus, low-frequency PA was associated with health benefits both in males (lower %fat) and females (higher VO(2)max/FFM). Probably due to the generally low fitness level of females and, hence, the high aerobic effort (%VO(2)max) required for exercise sufficient to impinge on fat stores, this was only achieved in females participating in higher weekly frequency (>/=3) of PA.

Absolute versus relative intensity of physical activity in a dose-response context

PURPOSE

To examine the importance of relative versus absolute intensities of physical activity in the context of population health.

METHODS

A standard computer-search of the literature was supplemented by review of extensive personal files.

RESULTS

Consensus reports (Category D Evidence) have commonly recommended moderate rather than hard physical activity in the context of population health. Much of the available literature provides Category C Evidence. It has often confounded issues of relative intensity with absolute intensity or total weekly dose of exercise. In terms of cardiovascular health, there is some evidence for a threshold intensity of effort, perhaps as high as 6 METs, in addition to a minimum volume of physical activity. Decreases in blood pressure and prevention of stroke seem best achieved by moderate rather than high relative intensities of physical activity. Many aspects of metabolic health depend on the total volume of activity; moderate relative intensities of effort are more effective in mobilizing body fat, but harder relative intensities may help to increase energy expenditures postexercise. Hard relative intensities seem needed to augment bone density, but this may reflect an associated increase in volume of activity. Hard relative intensities of exercise induce a transient immunosuppression. The optimal intensity of effort, relative or absolute, for protection against various types of cancer remains unresolved. Acute effects of exercise on mood state also require further study; long-term benefits seem associated with a moderate rather than a hard relative intensity of effort.

CONCLUSIONS

The importance of relative versus absolute intensity of effort depends on the desired health outcome, and many issues remain to be resolved. Progress will depend on more precise epidemiological methods of assessing energy expenditures and studies that equate total energy expenditures between differing relative intensities. There is a need to focus on gains in quality-adjusted life expectancy.

Low-frequency physical activity insufficient for aerobic conditioning is associated with lower body fat than sedentary conditions

We aimed to show the relationships between reported physical activity, fitness level, and body composition in healthy adult office-working Kuwaiti males (n = 45). Reported level of physical activity (group 0 = no routine exercise, n = 10; group 1 = routine exercise once per wk, n = 19; group 2 = routine exercise two or more times per wk, n = 16) was determined from recall questionnaires. Aerobic fitness levels were assessed from resting exercise heart rates and measurement of maximal oxygen uptake (treadmill exercise, Bruce protocol). Body composition was estimated from measurements of body weight, body height, and seven skin-folds. None of the subjects reported dieting to reduce or maintain their body weight. Despite minimal and not statistically significant differences in resting heart rates, VO(2)max, VO(2)max/kg body weight, and VO(2)max/kg lean body mass, the sedentary group (group 0) had a much higher (12--14 kg) average body weight, higher (12--13 kg) body fat, and thicker skin folds than the more physically active groups 1 and 2. Groups 1 and 2 did not differ significantly from each other with regard to fitness and body composition parameters. Thus, routine physical activities insufficient to result in aerobic conditioning were found to be associated with lower body weight and lower body fat compared to those present in subjects reporting the total absence of any routine physical activity. These data are consistent with the hypothesis that even mild levels of routine physical activity are associated with levels of energy turnover that allow less intense and/or frequent periods of positive energy balance, resulting in maintenance of lower body fat than in totally sedentary people. Frequency of participation in routine physical activities may also reflect the level of non-exercise related physical activities and thus relate to the ability to minimize weight gain.