by Sara Thompson and Fiona Callender
We extended our visit in Copenhagen to visit Professor Kristian Karstoft, thanks to a recommendation by his colleague Dr. Jonathan Little. Dr. Karstoft is a medical doctor at the University of Copenhagen who has focused on clinical research over the past five years. He does research on various chronic diseases; however, his bread and butter is using exercise training as treatment for patients with type 2 diabetes (T2D). 
Karstoft has developed what he believes is an optimal exercise training protocol for the management of T2D. Similar to Dr. Little at the University of British Columbia, Karstoft has found that “interval walking” elicits tremendous physical and health benefits for individuals with this disease. Individuals perform a 60-minute training session, in which they alternate between “fast-paced” and “slow-paced” walking every three minutes. Karstoft has done extensive testing on numerous protocols in which the length and ratio of walking intensity differs, however, he has found that the 60-minute 3-minute fast/slow protocol is ideal for physical fitness, body composition and glycemic control.
In one particular study, individuals were randomized into a control group (in which they continued their normal lifestyle), a continuous walking group, and an interval walking group (Karstoft et al., 2013). The continuous walking group performed 60 minutes of walking at a consistent intensity (approximately 55% of their peak energy-expenditure rate based on their baseline testing). The interval walking group also performed 60 minutes, however these individuals alternated between 3 minutes of high-intensity and 3 minutes of low-intensity walking. Participants performed this five times per week for four weeks. In order to monitor adherence and intensity, participants wore accelerometers and heart rate monitors during each training session.
Results of the study revealed that participants in the interval walking group had significant improvements in physical fitness, as measured by a 16.1% increase in maximal oxygen consumption (VO2max). This is significant as lower VO2max is a predictor for all-cause mortality and cardiovascular disease (Kodama et al., 2009). Additionally, individuals in the interval walking group had significantly lower body mass and adiposity following the 4-week intervention. This is particularly promising as T2D is associated with being overweight and obese. Interval walking also improved glycemic control. As discussed in a previous FTG article, T2D is characterized by insulin insensitivity and altered glucose regulation. To test the effects of training on glycemic control, participants wore a continuous glucose monitoring (CGM) system, a device inserted into abdominal subcutaneous fat tissue to continually monitor changes in glucose throughout the day. Results of this study revealed that participants in the interval training group had decreased mean and maximal glucose levels following the training period.
Karstoft discussed that one of the most surprising findings was that participants in the continuous walking group did not improve their health measures following the four-week study. Their VO2max, body mass and composition, and glycemic control was unchanged from the beginning to the end of the study. This is alarming as society encourages people to “just get out and walk”. However, Karstoft doesn’t want people to get the wrong message that physical activity doesn’t work. In fact, continuous walking seems to at least offset the deterioration in glycemic control that occurs in the control group. Instead, Karstoft aims to disseminate that individuals need to incorporate some form of intensity into their walking. He says that in general people select a pace that is too slow, so breaking up the workout into three minutes of fast walking followed by three minutes of easy walking facilitates that increase in exercise intensity.
One of the most fascinating observations by Karstoft and colleagues is that interval walking seems to be a superior training stimulus compared to continuous walking even after a single session! Karstoft and colleagues had ten T2D patients perform interval and continuous walking on separate study visits (Karstoft et al., 2014). Interval walking elicited improved glycemic control compared to the control session, however there were no differences between continuous walking and the control session.
Karstoft discussed how interval walking works for this population – the biggest hurdle is having people do it. During a recent study, adherence was around 89% (Karstoft et al., 2013), however patients tend to stop exercising once the study is over. Karstoft admits that this is likely because their training is no longer supervised, and having them come back for follow up testing is one possible solution to this problem. This would be kind of like giving someone a prescription for medicine and having them come back to test if it’s working. Karstoft’s lab is currently working on a smartphone app that helps some individuals adhere to a training program. He says that some people need to have something telling them when to exercise and what to do.
We had a great visit to the University of Copenhagen and we look forward to making a trip back there someday! Karstoft and his team of researchers have developed an “interval walking” protocol that improves various health markers in patients with T2D. This protocol is optimal for this population as most participants are in their 50’s and 60’s and can manage walking. This protocol is even practicable for individuals who have various complications of T2D such as obesity, hypertension and cardiopathy. Most importantly, this training program can be performed with minimal or no supervision, and can be done anywhere. You just need to grab a friend and go walk!
Sources:
Karstoft, K., Winding, K., Knudsen, S. H., Nielsen, J. S., Thomsen, C., Pedersen, B. K., & Solomom, T. P. (2013). The Effects of Free-Living Interval- Walking Training on Glycemic Control, Body Composition, and Physical Fitness in Type 2 Diabetic Patients. Diabetes care, 36(July 2012), 228-236.
Kodama, S., Saito, K., Tanaka, S., Maki, M., Yachi, Y., Asumi, M., Sugawara, A., et al. (2009). Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis. JAMA : the journal of the American Medical Association, 301(19), 2024-2035.
Karstoft, K., Christensen, C. S., Pedersen, B. K., & Solomon, T. P. J. (2014). The acute effects of interval- vs. continuous-walking exercise on glycemic control in subjects with type 2 diabetes: a cross-over, controlled study. The Journal of clinical endocrinology and metabolism, 99(July), jc20141837.
Karstoft, K., Winding, K., Knudsen, S. H., James, N. G., Scheel, M. M., Olesen, J., Holst, J. J., et al. (2014b). Mechanisms behind the superior effects of interval vs continuous training on glycaemic control in individuals with type 2 diabetes: a randomised controlled trial. Diabetologia, 57(10), 2081-2093.