Accumulated and continuous physical activity
Accumulated and Continuous Physical Activity, Which is better for you?Introduction
Physical activity (PA) is becoming increasingly important to our health and the effects it can have on our daily lives, yet most adults report not to be physically active (MMWR, 2005). The sedentary lifestyle being led by the public is having a detrimental effect on general health. The decline in PA over the years could be due to modern technology such as cars and computers (Haskell et al, 2007) which stops people from doing the simplest of things such as walking to the shops. Inactivity can cause major health problems and increases the risk of chronic illness such as cardiovascular disease (Booth et al, 2000) it leads to obesity, hypertension, thromboemlic stroke, type 2 diabetes, cancer (Kesaniemi, et al, 2001) and psychological impairments such as stress and depression. Even with these heightened risks people are still not changing their lifestyles, in 2005 23.7% of the American population were reported as undertaking no leisure time activity (MMWR, 2005). PA is beneficial to health having positive effects on cardiovascular and musculoskeletal systems and brings improvements in the metabolic and immune systems (Vuori, 1998).
Prior to the 1990s it was strongly believed that the way to improve health and fitness was to do 15-60mins of continuous moderate-vigorous exercise up to 3-5 days a week (Hardman, 1999). The problem with this amount and intensity of exercise is people are less likely to adhere to it and in essence end up doing none at all (Osei-tutu & Campagna, 2005). More recently the American College of Sports Medicine (ACSM) (Pate et al, 1995) have updated their recommendation to suggest that the general public should accumulate ?30mins of moderate exercise, on most, if not all days of the week. Exercise can be accumulated through small periods of activity (<10mins) such as walking to work or even gardening. Regular periods of PA can promote and maintain health thus preventing chronic disease and early death (Haskell et al, 2007). There is a vast amount of literature supporting both of these suggestions; however both cannot be right. The following sections will investigate whether continuous or accumulated exercise is better, or whether neither has a more beneficial effect.
Continuous Exercise
Multiple studies have provided evidence that continuous exercise is the best way to keep healthy, however these results are in direct contradiction to those for accumulated exercise. Fulton et al (2001) showed that continuous was better than accumulated exercise through a field evaluation of energy expenditure (EE). A total of 31 females were tested over 3 days; walking continuously for 30mins on one day, walking for three 10min sessions on another and refraining from PA all together on a third. The order of walking was set to meet participant’s preference. Participants wore a TRITRAC-R3D® accelerometer to estimate their daily EE and kept a diary to record the time, duration, mode and intensity of any PA in their lives lasting for ?5 minutes.
Results showed that EE differed significantly between the exercising groups and a control group. EE was significantly greater in continuous exercise compared to the accumulated exercise, with the difference being attributed to differences in trunk movement, movement intensity or duration. Therefore for the purpose of EE continuously walking gave a greater weight loss, by 60kcals, compared to accumulated walking.
However there are several limitations to this study that may have impacted the validity of the results. The study was based on self reporting measures and the measurements from the use of an accelerometer. Accelerometers are known to give inherent errors in estimation of EE and could therefore give inaccuracy in the level of energy actually being expended, if this was the case though, errors would have applied to all trials. Self reporting measures could quite easily have lead to participants making up diary extracts in attempt to please the experimenters or to appear to be sticking to the walking regime. Additionally monetary incentives were also given for completing the study, which could affect protocol adherence.
All sessions were completely unsupervised and pace was determined mainly by the participants themselves, supervision could have influenced the intensity and duration of the exercise leading to different estimates of EE. Additionally participants were not randomised to the 3 walking conditions, so EE may have been influenced as to which condition was performed first. Participants should have been randomised into conditions or should have done the sessions at the same time of day and in the same sequence, whilst being supervised. Unless these factors are controlled the conclusion that EE is better in continuous exercise cannot be drawn.
Osei-Tutu et al (2005) compared the effects of the new ACSM PA recommendation to the traditional recommendation, aiming to see how both impacted mood, VO2max and body fat percentage. In the study 40 sedentary individuals were randomly assigned to one of three groups (Control Group, short bout (SB) or long bout (LB) group). The exercise groups trained for 8 weeks, doing 30mins of walking/day for at least 5 days/week. Participants walked at 60-79% of their maximum heart rate (HR) which was established in pre-testing. The SB group accumulated 30mins of exercise in three 10min bouts, separated by at least 2 hours. The LB group performed one continuous bout of walking at a time of their choice, both groups were self monitored and told to schedule walking into their daily lives. They were taught how to monitor their HR to ensure they were working in their target zone, and where possible were allocated Polar Vantage XL HR monitors. Each group totalled 1110mins of walking and had psychological assessments taken pre-, mid- and post-testing as well as physiological assessments pre- and post-testing. The control group remained sedentary.
Results showed that VO2max significantly increased (P ? 0.05) in both exercising groups and decreased in the control group, the exercise groups did not differ from each other. The LB group showed a significant decrease (P ? 0.05) in percent body fat after 8 weeks compared to the SB and control group. Mood was affected in both exercising groups, with vigour activity significantly increasing and total mood disturbance significantly decreasing. Levels of depression-dejection decreased significantly in the LB group. Overall LB exercise was seen as a better way to improve VO2max and mood and decrease percent body fat.
Psychological assessments show that participants who receive positive effects from exercise have an increased chance of maintaining exercise. In the LB group one factor affected another; when more body fat was lost, mood improved and this led to better adherence to the program. Perhaps the 10min threshold is not sufficient enough to allow for significant mood benefits. Due to the positive effects of exercise on mood and therefore adherence, improving the results cannot be isolated to exercise on its own. If mood was to be studied in all experiments continuous exercise may always be perceived as the better option.
Osei-Tutu et al (2005) used a field based study, not dissimilar to that of Fulton et al (2001). Measures are mainly self-reported and not monitored by an investigator. Adherence to the exercise regime may have been affected and it is therefore unclear whether continuous exercise actually yields greater effects on health to that of accumulated exercise, which was the case in this study.
Accumulation of Exercise
Accumulation of ?30mins of PA is the currently accepted option for improving health. Altena et al (2004) compared postprandial triglyceride (TG) responses in subjects who performed a single session of continuous exercise versus accumulated SBs of exercise. In the study, 18 inactive normolipidemic individuals, performed three separate trials (one continuous 30min run, three 10min runs or no exercise at all) along with eating high fat meals (HFM) in a randomised order, separated by 7-10 days. Excluding a 9min warm up, both trials totalled 30mins of running at 60% of subjects VO2max and were conducted in the evening, 12 hours before HFM. Blood samples were taken in the fasted state, then every 2 hours for a total of 8 hours after the HFM. Samples were used to analysis plasma TG, total cholesterol and HDL-C.
Results showed plasma TG to be significantly lower in accumulated exercise compared to the control group, but continuous exercise was not different from accumulated or control group. With no food being consumed between accumulated exercise sessions, results indicate that SBs of exercise attenuate the effects of a HFM more so than continuous exercise and SB exercise is therefore better at lowering postprandial lipemia. Altena et al (2004) concludes that the public should exercise in short but more frequent bouts. Again, however, there are a number of limitations within this experiment that could impact the validity of the results.
There were no dietary restrictions, the study allowing participants to be “free-living” prior to consuming the HFM. Participants were not consuming the same amount of calories as one another and though asked to replicate their diet before each additional trial there is no certainty they did. Therefore the calories they consumed before the continuous exercise may have been of a greater amount compared to those consumed before the accumulated exercise. Blood samples taken after the HFM and the level of lipid within the blood cannot be isolated to exercise alone. Participants may have eaten less/more fat prior to the different trials and this could potentially alter the level of lipid within the blood, giving inaccurate results of postprandial lipemia.
During the accumulated trials, all exercise was performed over a short period of time and guidelines say that exercise should be accumulated throughout the day. In this study the 3 SBs were separated by 20mins of rest, with the next bout starting straight after. A 20min rest period is not sufficient enough to allow the body to recover and be in a non-exercised state so the benefits of accumulated exercise are more likely to replicate those of continuous exercise. Results given for postprandial lipemia to accumulated exercise are therefore similar to that of continuous exercise.
Park et al (2006) looked at the effect of accumulated and continuous exercise on blood pressure (BP) reduction in 20 pre-hypertensive adults. A randomised cross over design was conducted with ambulatory BP and HR variability being taken for 12 hours after either; accumulated exercise (4 sessions of 10mins) or one 40min continuous session of exercise. A control group also attended the lab but did no exercise. Trials were separated by 7 days to avoid any training effects. Exercise (walking on a treadmill) was performed at 50% of each participant’s VO2maxpeak; VO2 was measured in mins 2-4 and 6-8 of each session to confirm exercise intensity. HR, measured via ECG and BP via auscultation was used to monitor participants throughout. An accelerometer was also used to measure EE to allow control for variation in activities in participant’s daily life.
No significant difference (P = 0.894) in EE for the 12 hours post treatment were found for the three groups. Systolic BP (SBP) was reduced for 11 and 7 hours post exercise and diastolic BP (DBP) was reduced for 10 and 7 hours post exercise in the accumulated and continuous group respectively. The reduction in SPB was significantly greater (P = 0.045) after accumulated exercise compared to that of continuous exercise. The conclusions drawn state that accumulated PA appears to be more effective than continuous PA in the management of BP in pre-hypertensives.
In conclusion Park et al (2006) leans towards the use of accumulated PA to improve health. This controlled laboratory study can be seen as reliable and the effects of accumulated PA on BP are impressive. All recorded data was quantitative and not reliant on self-reporting which could lead to participant bias. The study also recorded baseline and post exercise measurements allowing comparison of the two. The drawback to this study is the use of one off bouts of PA. To make the results more reliable and respectable to the public the study should have been undertaken over a longer period of time. This would allow us to see if the effects of accumulated exercise are acute or sustained on reducing BP in pre-hypertensives.
No differences between continuous and accumulated exercise
It was originally thought that continuous exercise was the best way to improve health, so why has it now been assumed accumulated exercise is better? Many studies have compared the two and found no difference. Macfarlane et al (2006) found that the effects of accumulative exercise were not too dissimilar to those from continuous exercise on fitness levels. In the study 50 participants were randomly assigned to one of two gender matched groups; either a life style activity group (SB) or an exercise prescription model group (LB). Both groups were to accumulate 10-11 MET hours/week for the duration of the study. The LB group performed 30mins of light- moderate continuous exercise 3-4 days/week, while the SB group did 5 daily 6min sessions on 5 days/week. Adherence was assessed using a daily log, recording the time, duration, mode and rate of perceived exertion for each session, HR was also measured in sessions. Participants attended pre- and post-testing sessions, were phoned weekly and visited twice during the study.
Results show no difference between either group in EE and VO2max. Both groups accumulated more MET hours than they had been prescribed to do, but for the same duration the LB group managed to accumulate more EE than the SB group. VO2max significantly improved by 7.4% and 5.3% in the LB and SB groups respectively. Overall findings show that the effects of SB exercise can provide short-term improvements in cardiovascular fitness which is comparable to that of LB exercise.
Results suggest that either type of PA would enable the same benefits; however poor control of variables within the study lead to invalid results especially the non use of a control group, not allowing any comparisons. Without a comparison we cannot be certain that there are not any other variables effecting results.
Like many studies on PA, recording the amount of PA performed was self reported; participants could quite easily have done more exercise than prescribed and not reported doing so. This would lead to results which do not represent what is actually being investigated, and therefore not answering the question of which type of PA is better. The study does not provide any strong quantitative physiological data either. HR monitors were used but some data was not fit for analysis, and without strong data the conclusion cannot be seen as reliable. Additionally participants were not all working at the same intensity when exercising, which could have greatly affected results. A final problem is the number of sessions the SB group were required to perform; fitting 5 sessions of 6mins may have become impractical and allowed adherence to decline. If all sessions had been completed, accumulated exercise may have been seen as the better option compared with continuous exercise.
Murphy and Hardman (1998) also concluded that there was no difference between accumulated and continuous brisk walking. In the study 34 women participated in a 10 week brisk walking program and were split into one of three groups (SB walkers, LB walkers and control group). Walking pace was set at 70-80% of maximal HR based on baseline testing. Participants were asked to walk briskly and keep their HR in their designated zone using a HR monitor. Walking took place on 5 days/week for a duration of 30mins; women in the LB group did one 30min walk whereas women in the SB group did three 10min walks with a gap of ?4 hours. Walking was performed outside the laboratory with one day out of five being supervised, participants also filled in training diaries throughout. BP, blood lactate and anthropometry measures were taken at baseline and at the end of the study.
Results show that all measures of endurance fitness improved in the walking group, VO2max and VO2 at blood lactate concentration of 2mmol.L-1 increased significantly in the walkers relative to the control, but a significant difference was found between the LB and SB groups respectively. Body mass decreased in both walking groups, but only the SB were significantly different from the control group skin fold thickness decreased in both walking groups but again did not differ between LB and SB groups.
The findings that fitness improved to a similar level with three brisk walks as it does to one continuous 30min walk, prove that perhaps it does not matter which type of PA we choose to do. This study was well controlled and had large amounts of data to substantiate the conclusions. Baseline and post-test measures were undertaken which included exercise tests, anthropometry and BP. In the case of BP duplicate results were taken by an observer who was blinded to the participants walking regime, stopping any experimenter bias. When participants were joined once a week, investigators concealed their HR monitors to make sure that they were correctly pacing themselves. This prevented participants walking at the incorrect speed if for any reason their HR monitors were to break
The only drawback to this study is the use of a field based design, if the same study had been carried out within a laboratory all factors would have been isolated and the results gained would have been entirely due to the exercise performed. Performing almost all sessions without supervision could have lead to participants not adhering fully to the protocol or walking at the incorrect speed and the weather may also have been a confounding variable. Overall the results are consistent and reliable and the improvements in health can be isolated to the exercise being undertaken.
A final study by Schmidt et al (2001) also found no differences between SB and LB exercise on fitness and weight loss. In the study 48 overweight females were assigned to one of 4 groups (a control group, one 30min bout, 30mins split into two 15min bouts and 30mins split into three 10min bouts) and completed a 12 week aerobic exercise program, exercising at 75% of their HR reserve. Participants reported to the same designated exercise room during specific hours where an undergraduate student was in charge of recording attendance and HR. Exercise length increased from 15mins/day in weeks 1-2 to 30mins/day in weeks 5-12. Participants in the multiple bout groups were required to have a gap of at least four hours between sessions, thus eliminating residual physiological effects from the previous bout. HR monitors were worn throughout the exercise and participants were asked to stick to a self-monitored calorie restricted diet, of 80% of their resting EE (REE) throughout the study. Participants were also asked to wear a pedometer during waking hours so that the number of miles walked when not exercising could be recorded. Participants attended pre and post assessments where height and weight, circumference of hips, waist, thighs and upper arms as well as skin fold thickness at seven sites were measured as well as oxygen uptake and REE.
The results from this study show that VO2max increased significantly in all 3 exercise groups compared to the control. There was a significant decline from baseline to post-treatment in mean weight loss, body mass index, sum of skin folds and sum of circumference measures in exercising groups. Therefore exercise which is accumulated in several SBs does not differ to one LB of exercise in the effects it has on aerobic fitness or weight loss.
The laboratory based design of this study means all variables were well controlled and therefore the conclusions drawn can be seen as reliable. All results were obtained through scientific measures and the data is quantitative rather than self-reported. Participants were continuously monitored throughout and were checked upon if they missed a session, causing adherence to be high. A drawback with this study is that participants were asked to self-monitor their calorie constricted diet, potentially leading to error in the actual amounts of calories consumed. Overall though, the study was well controlled and showed that exercise must be the factor effecting fitness and weight loss.
Conclusion
There is a vast array of literature available that leads to confusion over which type of PA (accumulated or continuous) we should perform to maintain our health. From the articles evaluated it would seem that both types of PA improve health and fitness levels. The majority of studies that are well controlled for indicate that both types of PA give the same effects and so doing either are beneficial. However, I would conclude that accumulated PA is better as it is much easier to fit into a busy lifestyle; it requires no changing of clothes or going to a designated workout area, and is therefore more achievable (Schmidt et al, 2004). Accumulated PA gives multiple health benefits such as attenuating postprandial lipemia (Altena, 2004), increasing high density lipoprotein cholesterol (Aldred et al, 1994) and helping with weight loss. It has also been shown to improve aerobic fitness (Murphy et al, 2002) and blood lactate response to sub-maximal exercise (Murphy and Hardman, 1998).
The drawback for accumulated PA is that it has been shown to give less overall EE then continuous PA (Fulton et al, 2001). Continuous PA has also been shown to improve VO2max and has a positive effect on personal mood (Osei-Tutu et al, 2005). That said continuous exercise is more likely to be of a higher intensity and therefore has negative effects such as getting sweaty or having to go to a required location to participate.
Both types of PA have pros and con, equally having positive effects on health, but as our lives are becoming increasingly busy it would be easy to count walking to work as one bout of PA rather than having to make the effort to go to the gym.
