Physical inactivity is the fourth largest risk factor for mortality and a major risk factor for non-communicable diseases (World Health Organization, 2009). The worldwide prevalence of non-communicable diseases, including diabetes, cardiovascular disease, and cancer, is increasing and they are estimated to account for 63% of global deaths (World Health Organization, 2011). Combined evidence from 76 countries suggests that approximately 25% (range 2.6%-62.3%) of people are currently sedentary (Dumith et al., 2011). Thus, one of the leading targets in the prevention of non-communicable diseases is to enhance the overall intensity and volume of physical activity. The prevention of physical inactivity and related diseases pertains all professionals working in health care, especially exercise physiologists and physiotherapists who have expertise in exercise prescription.
Physical exercises are often prescribed as a first line of defence against inactivity. Such interventions, however may result in compensatory decrease in nonexercise physical activity (King et al., 2007). Nonexercise physical activity has been shown to decrease with cycling (Goran and Poehlman, 1992, Morio et al., 1998, Manthou et al., 2010), walking (Colley et al., 2010), or combined resistance and aerobic training (Meijer et al., 1999) exercise interventions. However, the current evidence regarding the compensatory response is inconsistent (Hollowell et al., 2009, Turner et al., 2010). In previous studies physical activity measurements have accounted only for a small portion of the intervention and focusing mainly on the change in total energy expenditure. Thus, the effect of exercise on non-exercise physical activity during the whole intervention remains to be determined, especially in the sense of intensity and volume. Better understanding of compensatory behavior, could enable more personalized and effective dosage of exercise for different impairments and medical conditions.
The purpose of this study was to measure total physical activity during an exercise intervention and to investigate the effects of a 12-week structured aerobic training (Nordic walking) and power-type resistance training on the intensity and volume of total physical activity and its subcategories. An additional aim was to define the correlates for changes in physical activity.
Twenty-three (n = 23) male volunteers from a larger (n = 144) randomized controlled trial (ISRCTN97931118), who had completed physical activity questionnaires were included in this study. The inclusion criteria for the trial were: male, 40-65 years of age, body mass index 25.1-34.9 kg * [m.sup.-2], over 12 points in the Finnish diabetes risk test (Lindstrom and Tuomilehto, 2003), impaired glucose regulation (impaired fasting glucose 5.6-6.9 mmol * [L.sup.-1] and/or impaired glucose tolerance 7.0-11.0 mmol * [L.sup.-1]), no other metabolic diseases, and a successfully passed medical examination. Criteria of exclusion were as follows: previously detected IGR and engagement in any customized diet or exercise program, engagement in very vigorous habitual physical activities, or usage of medication that affects glucose balance. Participants that fulfilled the criteria and gave their written informed consents were initially randomly assigned (1:1:1) to a Nordic walking (NW, n = 48) group, a power type resistance training (RT, n = 49) group, and a non-exercise control (C, n = 47) group. Of that initial sample of subjects, twenty-three subjects returned the completed physical activity questionnaires at least from a 1-week period before the intervention and from a 10-week period during the intervention, and formed the sample for the present study. Altogether, the present study included seven (n =7) subjects from the NW-group, eight (n = 8) from the RT-group, and eight (n = 8) from the C-group. The baseline characteristics of these subjects compared to the other who completed the initial trial have been shown in Table 1. As shown in Table 1, there were no significant differences in the baseline characteristics between those who were included in this study (n = 23) and those who completed the trial but were excluded from this study due to the insufficient physical activity data (n=93). This study was approved by the Coordinating Ethical Committee of the Hospital District of Helsinki Finland. The funding organisations had no role in the collection, analysis, or interpretation of the data of this study, nor did they have the right to approve or disapprove the publication of this manuscript.
A detailed description of the exercise programs has been previously reported (Venojarvi et al., 2013; Wasenius et al., 2014). In brief, both exercise groups completed a 12-week structured physical exercise program, which included 3 training sessions per week (non-consecutive days) each lasting approximately 60 minutes. The NW-group performed progressive endurance training at 5060% of heart rate reserve (HRR) in weeks 1-4, 60-70% of HRR in weeks 5-8, and 70-80% of HRR in weeks 9-12. At the beginning of each session walking (5 min) and stretching of the main muscle groups were performed to warm-up the body. For cool-down, stretching activities were repeated at the end of each session. The RT-group performed power-type resistance training exercises for main muscle groups with a maximal contraction velocity and an external load from 50% to 80% of the estimated exercise specific maximal strength capacity. The load (from 50% up to 80% of 1-repetition maximum) and number of sets increased (from 1 to 4) while the number of repetition decreased (from 10 to 3) progressively throughout the intervention. Before and after the intervention exercise session cycling or rowing with the ergometer (5 min) and stretches of the main muscle groups were performed to warm-up and cool-down the muscles. The adherence and dose of structured exercise interventions (NW and RT) compared to the other subjects who completed the initial trial (excluded from this study) are shown in Table 2. In the RT-group the intensity was slightly lower for those who were included while there was no significant difference in the NW-group. The dose of the NW-group was significantly greater compared to the RT-group for those who were included, which is consistent with a previous report (Wasenius et al., 2014).
All participants in all three groups were advised not to change their habitual physical activity or lifestyle during the intervention. The C-group participated in the general lectures given to all participants before the intervention, but received no other exercise, diet, or any other kind of intervention.
Body height was determined to the nearest 0.5 cm and body weight (kg) with calibrated weighing scales to the nearest 0.1 kg. BMI was calculated by dividing body weight (kg) with height in meters squared (kg * [m.sup.-2]). Body fat (kg) and fat per cent (%) were measured with electrical bioimpedance (Korea Inbody 3.0, Biospace Co., Seoul, South Korea). Maximum oxygen uptake ([VO.sub.2peak]) was estimated directly during a continuous incremental cycle ergometry until volitional exhaustion or subjective maximum.
Physical activity was measured weekly with specific questionnaires before (4 weeks) and during (12 weeks) the intervention. The questionnaires were completed in sets of 4 weeks. For week 1 participants were instructed to complete the questionnaire accurately in a diary manner and complete the following 3 weekly questionnaires retrospectively while using the first questionnaire as a guiding rule. The questionnaire measured physical activity throughout the day (24 h per day, 7 days a week) and it was divided into the following...