Effect of Exercise Training Intensity on Abdominal Visceral Fat and Body Composition

Results

Pretraining Characteristics and Exercise Adherence

Table 1 , Table 2 and Table 3 present the mean ± SD pre- and posttraining values for the metabolic syndrome parameters, body composition, cardiorespiratory fitness, physical activity, and BMR by treatment condition. There were no significant differences among the three conditions at baseline for any outcome measure (all P > 0.1; Table 1 , Table 2 and Table 3 ). Table 4 presents the summary data for exercise adherence, volume, and intensity. Both the LIET and the HIET groups had similar exercise adherence, with ~79 ± 3% and ~83 ± 3% of the assigned exercise sessions completed within each exercise condition, respectively. We did not observe a differential rate in dropouts among the three conditions (Fig. 1). During LIET exercise sessions, the mean RPE was ~11; for HIET, the mean RPE was ~15 during the HIET sessions and ~12 during the LIET sessions. By design, the mean velocity per session and the mean RPE per session were significantly higher in the HIET group during their HIET days compared with the LIET group. There were no statistically significant differences between the two training groups for the total estimated caloric energy expenditure.

Metabolic Syndrome Parameters

By design, all participants had elevated waist circumference and at least two of the following: had elevated fasting blood glucose, had low HDL-C, had hypertriglyceridemia, and were normotensive to mildly hypertensive at baseline ( Table 1 ). HIET significantly reduced waist circumference (P = 0.001), which was significantly greater than the reductions observed in response to Control and LIET (P = 0.039 and P= 0.035, respectively; Table 1 ) after adjusting for the baseline values. LIET significantly reduced systolic blood pressure (P = 0.002), which was significantly greater than the reduction observed in response to Control (P = 0.023; Table 1 ) after adjusting for the baseline values. However, the remaining metabolic syndrome parameters remained unchanged.

Body Composition

HIET significantly reduced total abdominal fat (P < 0.001, Table 2 ), AVF (P = 0.010; Table 2 and Fig. 2C), and abdominal subcutaneous fat (P = 0.034; Table 2 and Fig. 2D) after adjusting for the baseline values. There were no significant changes observed in any of these parameters within the Control or the LIET conditions. The reductions in total abdominal fat and abdominal subcutaneous fat cross-sectional areas in the HIET condition were significantly greater than those observed in the LIET condition (P = 0.017 and P = 0.033, respectively) after adjusting for the baseline values. Although the reduction in AVF within HIET condition (-24 cm²) was much greater than that observed within the Control condition (-2 cm²) and the LIET condition (-7 cm²), these differences did not reach the level of statistical significance across conditions (P = 0.098 and P = 0.153, respectively). HIET also significantly reduced total midthigh fat (P = 0.001; Table 2 and Fig. 2E). We did not observe a significant change in total midthigh skeletal muscle among the three treatment conditions (P > 0.1; Table 2 and Fig. 2D). HIET significantly reduced total body weight (P = 0.013), body mass index (BMI; P = 0.009), and fat mass (P = 0.011; Table 2 ).

(Enlarge Image)

Figure 2. Effects of 16 wk of no-exercise training (Control, n = 7), low-intensity exercise training (LIET, n = 11), and high-intensity exercise training (HIET, n = 9) on abdominal subcutaneous abdominal fat (B), visceral fat (A), total midthigh skeletal muscle (C), and total midthigh fat (D) cross-sectional area. The values shown represent the individual percent change (%Δ) values (open circles), the mean %Δ values (solid square), the median %Δ values (box split), the lower (bottom of the box) and upper quartiles (top of the box), and the minimum and maximum %Δ values (lines) by condition. Two-way, mixed-effects ANCOVA with repeated measures was used to examine mean differences in pre- to posttraining values, with the baseline values serving as the covariate (for details, see Methodology section). For all analyses, linear contrasts of the means were constructed to test our a priori hypotheses. Fisher's restricted least significant differences criterion was used to maintain the a priori type I error rate of 0.05.

Cardiorespiratory Fitness

LIET and HIET significantly elevated V˙O_2peak (P = 0.047 and P = 0.004, respectively; Table 3 ). The increase in V˙O_2peak in the HIET condition exceeded that for Control and LIET conditions (P= 0.016 and P = 0.078, respectively; Table 3 ). V˙O₂ LT was unchanged after training in all three conditions (all P > 0.1; Table 3 ). LIET and HIET resulted in significant elevations in peak treadmill velocity (P = 0.006 and P < 0.001, respectively; Table 3 ). HIET induced a greater elevation in peak treadmill velocity than Control and LIET (P = 0.005 and P = 0.056, respectively; Table 3 ).

BMR, Physical Activity, and Diet

We did not observe any significant changes in the BMR ( Table 3 ) or substrate oxidation assessed using the basal RER (data not shown). We also did not observe any significant changes in total physical activity in response to the three treatment conditions ( Table 3 ). A limitation of the present study isthat due to incomplete dietary data, we were unable to adequately analyze the dietary records for pre- to posttraining changes in caloric intake.

Spearman Correlation Analyses

Pooled Spearman correlation analyses (N = 27) were conducted to examine the relationships among pre- to posttraining changes weight, percent fat, AVF, and the metabolic syndrome parameters. Weight loss was positively associated with reductions in triglycerides (r = 0.56, P = 0.002) and SBP (r = 0.44, P = 0.022). Fat mass loss was also positively associated with (r= 0.49, P = 0.009) triglycerides.

Med Sci Sports Exerc. 2008;40(11):1863-1872. © 2008  American College of Sports Medicine

The results of the present study do not constitute endorsement by the ACSM.