Methods

(Summary)

This study was a 16-week randomized controlled trial. Sedentary prediabetic women were recruited from the Harrisonburg, VA area and randomly divided into two groups: Running-Sprint Interval Training (R-SIT) or Moderate Intensity Training (MIT).  Additionally, all participants attended 16 weeks of Diabetes Prevention Program (DPP) education with trained lifestyle coaches. Data was collected at baseline, midline, and post intervention and included: Framingham Risk Score (FRS), Vascular Age (VA), Blood Pressure (BP), Total Cholesterol (TC), High Density Lipoprotein Cholesterol (HDL-C), Low Density Lipoprotein Cholesterol (LDL-C), Very Low Density Lipoprotein Cholesterol (VLDL-C), Triglycerides (TG), body weight, height, and cardiovascular fitness level (VO2max). 

Participants were screened to ensure that they met the requirements to participate in the study. They were classified as “low” or “moderate” risk according to American College of Sports Medicine (ACSM) risk categories and had to be able to perform all-out efforts on a treadmill. Additionally, they had to be in overall good health with no previous CVD, pulmonary, or metabolic syndrome diagnosis. This study was approved by The Institutional Review Board at James Madison University. 

Participants attended two or three preliminary meetings prior to randomization: familiarization, fitness and anthropometric testing, and clinical testing. During the familiarization meeting participants discussed procedures, risks, and questions as well as completed an Informed Consent form and received a Three Day Food Intake Records (to be completed at home during two weekdays and one weekend day). The researchers provided participants with detailed verbal and written instructions on how to accurately collect Three Day Food Intake Records. A follow-up meeting with the participants was scheduled for a later date to review recorded food intake data. Records were analyzed using University of Minnesota Nutrition Data System for Research 2012 (Minneapolis, MN). 

For the clinical testing, participants were instructed to fast for 8-10 hours and report to a clinical lab for a blood draw administered by a certified phlebotomists. FRS was calculated using a calculator downloaded from www.framinghamheartstudy.org and the results from the blood draws. The CVD risk calculator uses age, gender, total cholesterol, HDL-C, smoking habits, and systolic BP to estimate the risk of non-diabetics between the ages of 30-74 who have no previous heart disease diagnosis.

General Training Protocol: 

Participants met three times per week for 34-84 minutes of supervised trainings. Both training protocols were broken up into four progressing blocks consisting of four weeks per block (see Table 1). Prior to all exercise resting BP and resting HR were recorded in the seated position. Participants began each training with a warm-up that consisted of five minutes of dynamic stretching plus five minutes of walking on the treadmill at a self-selected speed with no incline (0% grade). Total warm-up time was 10 minutes. Participants ended each session with a five minute treadmill cool down at a self-selected speed and 0% grade. Immediately following treadmill cool down, final HR and RPE were recorded.  Participants then completed five minutes of dynamic stretching. Total cool down time was 10 minutes. After cool down and a brief period of rest, resting BP was measured and recorded. Every four weeks, training progressed for both groups.  

Details on Training Protocols: 

R-SIT Group: Immediately following warm-up, participants began interval training. An interval was defined as 30-seconds of all-out sprint at a self-selected speed and grade, followed by four minutes of active recovery at self-selected speed and 0% grade. Participants received encouragement from the researchers to sprint as fast as possible to ensure that maximal effort and heart rate was achieved. HR was recorded at the end of each active recovery and at the end of each sprint. RPE was recorded at the end of each sprint. Every four weeks the training progressed as follows: weeks 1-4, four intervals; weeks 5-8, six intervals; weeks 9-12, eight intervals; and weeks 13-16, 10 intervals. 

MIT Group:  Immediately following warm-up, participants began moderate intensity training at 45-55% Heart Rate Reserve (HRR). HRR was calculated by subtracting resting HR and maximal heart rate. The result was then multiplied by 45-55% and added to resting HR to ensure target HR. HR was recorded every five minutes. Every four weeks the training progressed as follows: weeks 1-4, 30 minutes; weeks 5-8, 40 minutes; weeks 9-12, 50 minutes; and weeks 13-16, 60 minutes.

All statistical data was analyzed using SPSS 21.0 statistical software package. Paired sample and independent sample t-test were used to compare the relationship of the variables. Significance level was set a priori at p < 0.05.