Understanding the relationship between exercise intensity and glucose metabolism is crucial for providers managing metabolic function and exercise protocols. Different cardiovascular (cardio) zones, defined by exercise intensity, distinctly influence glucose utilization and insulin sensitivity. Continuous glucose monitors enable a more detailed view of how a client’s body responds to various forms of exercise and cardio zones, empowering an individually tailored care plan.
Cardio Zones and Energy Utilization
Cardio zones are typically defined as percentages of an individual’s maximum heart rate (MHR), which is often calculated as 220 minus age. Each zone reflects a range of exercise intensities:
- Zone 1 (50-60% MHR): Very Light Intensity
- Activities: Gentle walking, light stretching.
- Talk Test: Able to converse as normal
- Energy Source: Primarily fat oxidation.
- Impact on Glucose: Minimal immediate effect on blood glucose levels; however, regular engagement can enhance insulin sensitivity over time (Perry et al., 2008).
- Zone 2 (60-70% MHR): Light Intensity
- Activities: Brisk walking, light jogging.
- Talk Test: Able to hold a conversation.
- Energy Source: Increased fat utilization with some carbohydrate (glucose) involvement.
- Impact on Glucose: Increased glucose uptake by muscles; beneficial for improving insulin sensitivity and blood sugar control (Hawley & Gibala, 2009).
- Zone 3 (70-80% MHR): Moderate Intensity
- Activities: Steady-state running, cycling.
- Talk Test: Speaking reduced to sentences.
- Energy Source: Balanced use of carbohydrates and fats.
- Impact on Glucose: Increased glucose uptake to meet energy demands; beneficial for cardiovascular fitness, and blood sugar levels.
- Zone 4 (80-90% MHR): High Intensity
- Activities: Fast running, high-intensity interval training (HIIT).
- Talk Test: Speaking Reduced to words.
- Energy Source: Predominantly carbohydrates through anaerobic glycolysis.
- Impact on Glucose: Significant glucose utilization. Exercise performed at this level is likely to cause a temporary glucose spike (up to two hours) as glucose enters the bloodstream for immediate utilization. This spike is paired with enhanced insulin sensitivity for up to 72 hours after the workout is completed (Galbo, 1983)
- Zone 5 (90-100% MHR): Maximum Effort
- Activities: Sprinting, maximal effort exercises.
- Talk Test: Talking reduced to sounds.
- Energy Source: Almost exclusively carbohydrates.
- Impact on Glucose: Rapid glucose consumption; primarily used for short-duration, high-intensity efforts. Intense exercise of this nature often causes a temporary glucose spike as glucose enters the bloodstream for immediate utilization. Insulin sensitivity is heightened for up to three days following these workouts (Adams, 2013).
Implications for Glucose Management
Engaging in regular exercise across these zones can improve insulin sensitivity and glucose metabolism. In addition to each zone having a unique impact on glucose levels, High-Intensity Interval Training (HIIT) has been shown to improve blood sugar levels, contributing to a reduction in HbA1c over time.
To gain deeper insight into a client’s metabolic function, it’s helpful to monitor glucose responses to different exercise intensities. Continuous glucose monitors are a great tool for clients to better understand how their body is responding to various workouts, both in the moment and in the days following.
Recommendations for Providers
- Personalized Exercise Protocols: Tailor exercise programs to individual patient profiles, considering factors such as age, fitness level, and specific metabolic goals.
- Monitoring and Education: Incorporate continuous glucose monitoring technology so clients can see their glucose levels before, during, and after exercise sessions to understand their unique responses and adjust management strategies accordingly.
- Integration of Exercise Modalities: Incorporate a mix of aerobic and resistance training to optimize glucose metabolism and overall health outcomes.
Incorporating CGMs as part of care plans enables providers and their patients to comprehensively understand the effects of various exercise intensities on glucose dynamics. Using this data, healthcare providers can more effectively guide patients in managing their metabolic health through tailored physical activity care plans.
References
- Adams OP. The impact of brief high-intensity exercise on blood glucose levels. Diabetes Metab Syndr Obes. 2013;6:113-22. doi: 10.2147/DMSO.S29222. Epub 2013 Feb 27. PMID: 23467903; PMCID: PMC3587394.
- Galbo, H. (1983). Hormonal and metabolic adaptation to exercise. Thieme-Stratton Inc.
- Hawley, J. A., & Gibala, M. (2009). Exercise intensity and metabolic adaptations: Role of skeletal muscle fiber type recruitment. Current Opinion in Clinical Nutrition & Metabolic Care, 12(4), 366-372.
- Little, J. P., Safdar, A., Cermak, N., Tarnopolsky, M. A., & Gibala, M. J. (2011). Acute endurance exercise increases the nuclear abundance of PGC-1α in trained human skeletal muscle. American Journal of Physiology-Endocrinology and Metabolism, 300(1), E65-E71.
- Perry, C. G., Heigenhauser, G. J. F., Bonen, A., & Spriet, L. L. (2008). High-intensity aerobic interval training increases fat and carbohydrate metabolic capacities in human skeletal muscle. Applied Physiology, Nutrition, and Metabolism, 33(6), 1112-1123.
- Yardley, J. E., Kenny, G. P., Perkins, B. A., Riddell, M. C., Malcolm, J., & Boulay, P. (2013). Effects of performing resistance exercise before versus after aerobic exercise on glycemia in type 1 diabetes. Diabetes Care, 35(4), 669-675.