Relationship Between BMI & HRR After 4 Weeks of Aerobic Training
Condition: Overweight
MeSH terms: Overweight
Study type: Interventional

Summary: 
      World Health Organization (WHO) defined body mass index (BMI) as the ratio of weight in
      kilograms to the square of the height in meters (kg/m2). BMI has been used widely to diagnose
      obesity as it is a simple method to be carried out and is also inexpensive. According to WHO,
      there were 1.9 billion overweight individuals in 2014 with the age of 18 years old or above.
      Of 1.9 billion overweight individuals, there were 600 million obese adults. The prevalence of
      cardiovascular disease is higher among the overweight and obese individuals compared to
      individuals with normal body mass index. This probably is due to altered cardiovascular
      autonomic regulation. The risk of getting cardiovascular diseases is also higher among
      physically inactive individuals. As much as 60% of American adults are not regularly active
      and 25% of them are not active at all. Obese and overweight individuals tend to be physically
      inactive and it has been shown that there is a negative relationship between BMI and heart
      rate recovery (HRR). HRR is defined as difference in heart rate between maximum exercise and
      1 minute later during recovery period after stopping of exercise. HRR after exercise stress
      is due to withdrawal of sympathetic nervous system and the reactivation of parasympathetic
      nervous system. Parasympathetic nervous system is altered in obese individuals therefore
      leading to poor HRR after exercise. Aerobic training not only can reduce the body composition
      but also improves the autonomic cardiovascular control. There is limited literature support
      for any study which shows that potential of 4 weeks aerobic training can influence the heart
      rate recovery in sedentary healthy adults. Most of studies conducted were using minimum of 6
      to 8 weeks of aerobic training. The potential of 4 weeks of aerobic training in improving the
      autonomic nervous system among sedentary adults is still unclear. Therefore, we hypothesized
      in our study that there will be effect of 4 weeks of aerobic training on vagal modulation.
    

Detailed description: 
      Obesity is a complex health issue that results from various causes and contributing factors.
      Individual factors like genetics and behavior may contribute to overweight and obesity.
      Genetics played an important role in increasing hunger and food intake of individuals. A few
      examples of common diseases that are related to obesity are type-2 diabetes, stroke, coronary
      heart disease and some types of cancer. All these obesity related diseases may not be fully
      reversible even after weight loss . Body mass index (BMI) is used widely as a screening tool
      to assess overweight and obesity. Based on the World Health Organization (WHO) international
      classification of BMI, individuals are considered as obese if their BMI value is equal to 30
      kg/m2 or higher and overweight if BMI is 25-29.9 kg/m2. A study was conducted in USA to find
      the prevalence of obesity among children and adults. Researchers attempted to predict the
      childhood obesity and analyse the obesity trend among adults in United States. The results of
      the study showed that the prevalence of obesity among children were 16.9% and adults were
      34.9%. There were no obvious changes in prevalence of obesity among children and adults in
      between 2003-2012 in United States (1). It cannot be denied that there is a link between
      increasing rate of obesity and increasing medical spending. Medical spending for obese
      individuals was 42% higher compared to those with normal body weight (2). The researchers
      reported in their study that obesity was one of the factors that became an economic burden
      for both public and private payers. South East Asia and Western Pacific countries suffer from
      diseases associated with obesity such as cardiovascular diseases and diabetes. Malaysia is
      the country the highest rate of obesity in South East Asia (3). Studies have showed that
      autonomic nervous system is associated with obesity. In 2001, a study was conducted to
      identify the effect of weight loss on autonomic nervous system. The findings showed that the
      activity of parasympathetic nervous system increased with weight loss and cardiac vagal tone
      improved significantly after weight loss (4). Cardiac vagal tone is controlled mainly by
      parasympathetic nervous system and this helps to improve the heart rate recovery (HRR). There
      are two phase of heart rate recovery, fast and slow phase. The fast phase is due to cardiac
      parasympathetic reactivation while the slow phase is because of cardiac sympathetic
      withdrawal. If there is any disturbance of the autonomic nervous system then the HRR will
      slow down (5). Therefore, HRR can be used to assess the cardiac autonomic function and as a
      marker of cardiac vagal tone. Abnormal heart rate recovery after exercise stress can be
      considered as dysfunction of autonomic nervous system. It has been suggested in several
      studies that heart rate recovery after exercise stress is slower among obese individuals
      compared to BMI individuals. A study was conducted to identify the relationship between heart
      rate recovery and body mass index. The finding showed that there was a negative association
      between heart rate recovery and body mass index. 3.5% of 2443 individuals presented with
      delayed decrease heart rate recovery. The prevalence of decreased heart rate recovery was
      higher among overweight and obese groups (6). In another study similar findings were
      observed. Researchers concluded that obese individuals are more likely to have an impaired
      heart rate recovery during the recovery phase after exercise (7). Aerobic training improves
      the autonomic cardiovascular control. A study on 4 weeks of aerobic training was done to
      identify its effects on cardiac vagal tone. Authors reported that 4 weeks of treadmill
      aerobic training was able to improve the autonomic nervous system among pre-hypertension
      individuals (8). The aerobic training consisted of 30 minutes treadmill exercise at 65% of
      maximum oxygen consumption. Another study showed the similar results in which the autonomic
      nervous system was improved after 6 months of moderate intensity aerobic training (9). The
      aerobic training was carried out 1 hour each session with 2 sessions in one week for 6
      months. The present systematic review shows that aerobic training has been proven to be
      effective in increasing the heart rate recovery among subjects with established heart disease
      (10). The effects of 4 weeks of aerobic training in improving the cardiac vagal tone among
      sedentary healthy adults are still unclear. Therefore, we aim to study the effects of 4 weeks
      of aerobic training on vagal modulation.
    

Intervention name(s): 4 weeks of Aerobic Training
Intervention type(s): Procedure
Intervention description(s): The duration of aerobic training was 40 minutes for each session and 3 days per week with the intensity of 75-80% of their maximum heart rate. The participants were needed to walk or jog on treadmill during the first 10 minutes at the intensity of 50-60% of maximal heart rate (HR max). The aerobic training was followed by 4 x 4 minutes intervals at 75-80% HR max. The participants were given 3 minutes active breaks in between the intervals in which they can either walk or jog at 50-60% of maximal heart rate.
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Intervention model description: Same intervention (4 weeks of aerobic training) was given to 2 different groups (Normal BMI group & Overweight BMI group).
Masking: Single (Outcomes Assessor)
Primary purpose: Treatment
Keywords: Overweight BMI Individuals; Normal BMI Individuals; Recovery Heart Rate