The data from the study confirmed that a moderate intensity aerobic exercise-training programme performed 4 times a week could be successfully implemented within the workplace during working hours. Furthermore, it was demonstrated that it was effective at reducing risk factors associated with cardiovascular disease, and at improving physiological capacity within previously sedentary individuals. Specifically, significant improvements were found in peak oxygen consumption (VO2 peak
), economy of absolute oxygen utilization at both 2 minutes (2minVO2
) and 4 minutes (4minVO2
), and C-reactive protein (CRP) concentration. These results confirm previous reports showing that improved cardiovascular fitness, or physical activity level reduces cardiovascular risk, with a particular association with lower CRP levels [9
]. This is the first report combining objective physiological outcome measures with objective monitoring of the training programme to demonstrate the type of exercise that can be effectively carried out during working hours, while still providing health related benefits.
At the end of the 8-week intervention period absolute VO2 peak increased significantly by 5 % in the exercise group, while it decreased significantly by 6 % in the control group. There was no significant change in peak heart rate in the exercise group, but there was a significant reduction in peak heart rate in the control group, suggesting that a decline in effort contributed to the observed fall in VO2 peak. Absolute 2minVO2 and 4minVO2 decreased significantly by 17 % and 11 % respectively in the exercise group, while there was no significant change in the control group. Furthermore, as the exercise group averaged the completion of 81 % and 84 % of the prescribed exercise sessions between week 1 and week 4, and week 4 and week 8 respectively, it can be concluded that the progressive aerobic exercise training programme was not only effective at improving the physical fitness of a sedentary group of adults, but was also successful at increasing physical activity levels.
However although cardiovascular fitness and physical activity are positively related, research indicates that it is the former that is more closely linked to cardiovascular disease risk factors and disease, than actual physical activity level [25
]. As a consequence it has been shown that it is only those individuals who increase their VO2 max
, rather than their actual physical activity level that reduce their relative risk of cardiovascular disease risk factors [27
]. This has been attributed to a reduction in large artery stiffness, which may be mediated by concomitant changes in high-density lipoprotein (HDL) cholesterol and body weight [28
This holds relevance for the present study: after 8 weeks when the exercise group were not provided with any further progression or instruction to the exercise training programme VO2 peak
decreased by 2 %. In view of the 70 % completion of the 16 sessions, and the significant improvement in absolute 4minVO2
(-7 %), it appears probable that the intensity of the exercise performed within this time period was too low to challenge VO2 peak
. This is supported by evidence that indicates that VO2 max
has a modest association with physical activity, but a much stronger association with the mean intensity of the exercise [29
]. In view of this, and the cardio protective benefit of an increase in VO2 max
future research should evaluate the implication of a higher intensity workplace exercise training programme on the modification of cardiovascular risk profile, while assessing whether it remains successful at ensuring exercise adherence.
It appears that supervision and progression of the exercise programme may influence adherence [30
]. In the present study, at 8 weeks when no further progression or supervision to the exercise training programme was provided a reduction in the adherence of the training sessions occurred; 81 % and 84 % were completed in week 1 to week 4 and week 4 to week 8, while only 70 % were completed in week 8 to week 12. This could further highlight the need for employers to ensure the provision of additional support and progression to the original training programme for optimal participation of employees, and success of the programme.
The exercise group demonstrated a significant decrease in CRP of -0.4 ± 0.6 mg/L between week 1 and week 4, and -1.0 ± 0.4 mg/L between week 4 and week 8. However while this is in accordance with previous research [24
], it should be noted that due to a mean baseline value indicating high risk for CVD (> 3.0 mg/L), that the reduction would still result in a mean value indicating average risk of CVD (2.2 mg/L) [33
]. The mechanism behind such action remains unclear. It has been postulated that a reduction in CRP is attained via the positive benefit of exercise on BMI via modulation of the percentage of visceral fat and insulin receptor sensitivity [24
]. However, within the present study there was no such positive effect on body composition, or fasting glucose. Another potential explanation is that among unfit individuals there is a greater generation of reactive oxygen species via normal metabolic processes, and unaccustomed muscle stretching. This leads to subliminal injury of the myocytes, that causes both cell and tissue oxidative damage, leading to an inflammatory response [34
]. Evidence confirms that chronic exercise induces a mechanical resistance of the myocytes to stretching, and elevates endogenous antioxidant enzyme activity, which prevents excessive local inflammatory response [35
]. As there were significant gains in aerobic capacity within the exercise group it is plausible that this explanation provides a mechanism of action for the observed results.
No significant change was observed in IL-6 at any time point during the study. However there was a significant reduction in TNF-α between week 1 and week 4 in the exercise group. As TNF-α directly impairs glucose uptake and metabolism via a direct effect on insulin signal transduction, a reduction holds positive benefit for prevention of CVD [10
]. Thus despite the lack of a significant change in fasting glucose, there is still suggestive evidence that the training programme may accrue positive benefit for this specific risk factor.
Although the present study was successful at improving maximal and submaximal aerobic exercise capacity, it had no significant effect on fasting glucose or cholesterol, blood pressure or BMI. It is likely that the small sample size is responsible for such null findings. However it is also unsurprising for a number of reasons.
Firstly, although physical activity and exercise improves insulin sensitivity through a direct effect on the muscle (enhancement of insulin receptor autophsophorylation [36
], increase in GLUT-4 content [37
] and glucose transport-phosphorylation [38
], and a reduction in visceral obesity [39
], neither the exercise nor the control group exhibited impaired glucose tolerance (exercise = 5.04 ± 0.50; control = 5.11 ± 0.52 mmol/L) at baseline that would have required intervention modification. The same can be said for blood pressure, with all participants classified as normotensive (exercise = 118 ± 12/73 ± 10; control = 106 ± 10/69 ± 9) at baseline. Nevertheless, in view of the beneficial effect that exercise has on glucose tolerance, and evidence that those with low levels of physical fitness are shown to be at a relative risk of 1.52 for developing hypertension, when compared to highly fit individuals [6
], the use of exercise in aiding glycemic control, and the maintenance of healthy blood pressure should still be encouraged.
Secondly, regarding BMI, it should be considered that the aim of the training programme was not to directly target weight loss for a reduction of cardiovascular risk, but instead to improve physiological capacity, and biomarkers of cardiovascular profile. In accordance with this, and in the absence of dietary modification, it would have been unlikely that the 4 × 30 minute sessions per week would have provided the necessary negative energy balance stimulus of 500 – 1000 kcal·d-1
to achieve gradual weight loss (ACSM, 2006). Given that a BMI ≥ 30 kg·m-2
classifies obesity, concomitantly increasing the risk of hypertension, poor total cholesterol/HDL cholesterol ratio, coronary disease and mortality rate [40
], there is a need for future work place health promotion programmes to evaluate whether an aerobic exercise training programme specifically targeting weight loss and management as its primary outcome can be successfully implemented within the workforce.
A limitation of the present study was the failure to examine lipoprotein subfractions; small low-density lipoproteins (LDLs), high-density lipoproteins (HDLs), high-density lipoprotein subfractions (HDL3
), very low-density lipoproteins (VLDLs), and respective particle size, that better reflect CVD risk than absolute measures of cholesterol concentrations [41
]. In a recent study, Halverstadt et al (2007) concluded that an aerobic exercise training program consisting of 20 minutes, 3 days a week, progressively building up to a duration of 40 minutes and an intensity of 70 % VO2 max
for a period of 24 weeks, plus a weekend walk was successful at improving lipid subfraction profile and cardiovascular risk independent of diet and change in body fat. This is supported by several other studies, which also indicate an improved plasma lipoprotein profile with exercise training, exclusive of weight loss [5