3.1. Baseline Characteristics
At baseline, none of the demographic variables were significantly different when comparing ILI with DSE and these demographics have been published previously [10
] on a larger sample (n
= 5145); however, the data for this paper are only on those for whom we could calculate HRR at Year 1 (n
= 4503). The reasons for missing data have been explained in an earlier report by Jakicic et al. [14
]. These included scheduling issues, refusal to participate, medical reasons, and other reasons not specified.
3.2. Heart Rate Recovery Variables at Baseline and Year 1
The data at baseline and at Year 1 are presented for the heart rate variables in . Separate analyses were done for those with and without β-blocker usage. At baseline, none of the heart rate variables were significantly different between ILI versus DSE; this was true for both those with and without β-blocker usage. As expected, all resting, exercise, and recovery heart rate variables were lower for those on β-blockers and therefore subsequent bivariate and multivariate analyses were done only on those individuals who were not on β-blocker since the groups could not be combined in further HRR analyses.
Heart rate variables at baseline (a) and Year 1 (b) for participants with and without β-blocker use. Values are mean (SD).
At the Year 1 fitness assessment, which used a submaximal test [14
], all heart rate variables improved more (P
< 0.0001) in ILI versus DSE (), that is, resting heart rate was lower (72.8 ± 11.4 versus 77.7 ± 11.7
b/min), heart rate range increased (57.7 ± 12.1 versus 53.1 ± 12.4
b/min), heart rate at 2 minutes of recovery was lower (89.3 ± 21.8 versus 93.0 ± 12.1
b/min), and heart rate recovery was greater (41.25 ± 22.0 versus 37.8 ± 12.5
b/min) for ILI versus DSE, respectively. Nevertheless, ILI and DSE reached the same peak heart rate (130.5 ± 6.2 versus 130.8 ± 6.6
b/min for ILI versus DSE, resp.) confirming that both groups exercised to the same peak level during the exercise test. A similar trend was observed at Year 1 for those on β
-blockers with ILI exhibiting greater improvement in all heart rate variables yet still reaching the same peak heart rate during exercise.
3.3. Correlates of Heart Rate Recovery at Year 1
lists the Spearman correlation coefficients of 1-year Heart Rate Recovery with selected baseline measures, including age, duration of diabetes, waist circumference, BMI, HbA1c, and Triglycerides, and 1-year changes in weight and fitness. In this analysis, only those participants without β-blocker usage were included, and we used this analysis to determine which variables to include in the model used in . Not surprisingly, age was the strongest predictor of HRR (r = −0.22; P < .0001) since the key heart rate variables influencing the HRR also are lower with greater age, that is, lower peak HR with exercise and slower recovery after exercise with greater age. The second strongest predictor of faster HRR was the percentage of weight change (r = −0.18; P < .0001). Other variables that were associated with HRR were self-reported duration of diabetes (r = −0.11; P < .0001); hemoglobin A1c (r = −0.10; P < .0001); waist circumference (r = −0.10; P < .0001); percent fitness change (r = −0.09; P < .0001).
Correlations with Year 1 heart rate recoverya.
(a) Association of Year 1 Heart Rate Recovery with treatment group. (b) Association of Year 1 Heart Rate Recovery with combined weight and fitness changes.
Once these HRR predictor variables were identified, all participants (ILI and DSE) were divided into groups based upon (1) treatment group (); (2) age, gender, diabetes medication usage, CVD history, hypertension, waist circumference (); and (3) weight losses and/or fitness gains (). In every comparison, significant, or borderline significant relationships were demonstrated.
HRR according to treatment, select variables, weight loss, fitness gain, and combined effects of weight loss/fitness gain.
3.4. Influence of Weight Change and Fitness Change Gain upon Heart Rate Recovery at Year 1
Based on their one-year weight loss and fitness changes, participants who were not on a β-blocker were divided into four separate weight loss groups and four separate fitness gain groups, revealing that HRR improved with greater weight losses as well as with greater fitness gains (). Next, to examine the combined influences of weight loss and fitness gain on HRR, the participants were divided into 16 paired subgroups, based upon their combined weight and fitness losses and or gains (pairings noted in footnote in ). These groupings were used to form five separate groups, ranging from “Low” success in which participants either gained weight, lost fitness, or both to “High” success in which the participants achieved a 10% weight loss and 15% fitness gain at Year 1. This combined fitness/weight loss variable was significantly related to HRR at Year 1 and is illustrated in , where there is a marked improvement in those in the “High Success” group compared to all other groups with lesser weight loss and/or fitness gain.
Figure 1 Combined influence of weight loss and fitness gain on Heart Rate Recovery (left) and Comparison of DSE versus ILI (right). (Levels of success were determined by combinations of weight loss and fitness gain in the 8 subgroups as described in (more ...)
3.5. Multiple Regression Analysis for Heart Rate Recovery at Year 1
As a consequence of the intervention, ILI achieved a greater HRR than did DSE at Year 1 (). Even after adjusting for significant influencing variables (i.e., age, gender, duration of diabetes, HbA1c, BMI, waist circumference, etc.), the treatment group effect remained highly significant. Results for the multiple linear regression models are presented in . The least square means for HRR were 41.48 for the ILI and 37.94 for the DSE, resulting in a highly significant between group difference (P < .0001) (). A separate multiple linear regression model was fit to examine the differences in HRR among the five success groups (low, moderate low, moderate, moderate high, and high success). (). The least square means for HRR were 44.92, and 40.60 for the high and moderate high success groups, and 38.64, 38.34, and 37.79 for the moderate, moderate low, and low success groups, respectively. Adjusted pairwise group comparisons revealed that HRR for the high success and moderate high success groups were significantly higher than all lower success groups (P < .05). The moderate, moderate low, and low groups were not significantly different from each other.