In a recent study published in the journal Cellular metabolism, scientists examined physiological responses to exercise. They reviewed the adaptations that occur in tissues due to chronic exercise and their cumulative role in improving cardiometabolic health.
Review: Exercise induces tissue-specific adaptations to improve cardiometabolic health. Image credit: PeopleImages.com – Yuri A / Shutterstock
Health benefits of exercise
Studies show that people who exercise regularly and achieve recommended levels of physical activity have a lower risk of a wide range of diseases, including diabetes, cardiovascular disease, various cancers, and all-cause mortality. Current health recommendations suggest about 150 to 300 minutes of moderate-intensity exercise or 75 to 150 minutes of vigorous exercise, such as jogging, per week for adults. Additionally, an ideal workout routine should consist of muscle strengthening and activities to improve balance and endurance.
While factors such as resistance, number of sets, rest intervals, and repetitions can be modulated, the general principle of exercise regimens is progressive overload, where the load is increased progressively to enhance the adaptive response. The subsequent increase in energy demand also leads to changes in systemic metabolic homeostasis. The review examines the adaptive changes that occur in various tissues in response to chronic exercise. The review focuses on resistance and endurance exercise with studies involving human intervention.
Energy requirements and metabolic responses to exercise
Exercise generates intense energy demands, with an almost 100-fold increase in adenosine triphosphate (ATP) demands supplied by the activation of both aerobic and anaerobic pathways. Short but intense exercise results in increased utilization of anaerobic pathways and glycogen stores. However, longer duration exercise depends on aerobic metabolism for ATP production, resulting in increased oxygen consumption, muscle blood flow redistribution and cardiac output.
Furthermore, various signal transduction networks and transcriptional programs that respond to muscle contractions, energy availability, hormones, ions, oxygen availability, and redox state are activated during acute exercise. Transcriptional programs are activated by intense exercise in a tissue-specific manner through the involvement of various transcription factors, corepressors and coactivators.
The role of exerkinins in the exercise response
The review also discussed exerkinins, a term coined to describe exercise-induced signaling molecules that exert effects on various tissues through autocrine, paracrine and endocrine pathways. Exerkines include proteins such as cytokines, lipids, peptides, metabolites, and various types of nucleic acids such as mitochondrial ribonucleic acid (mRNA), micro-RNA, and mitochondrial deoxyribonucleic acid (DNA). The studies reviewed in the review discuss exerkines and their effects on various tissues and organs, including muscle, brain, liver, heart, intestine, adipose tissue, and pancreas.
Interleukin-6 (IL-6) has been the most extensively studied exerkin, and researchers have discussed the secretion of IL-6 as well as the metabolic effects of IL-6 on processes such as adipose tissue lipolysis, glucose uptake in resting skeletal muscle, glucose metabolism, exercise-related, and various other processes.
Multi-tissue coordination of acute exercise metabolism
Adaptations in different body systems
The review also examines various adaptations that occur as a result of chronic exercise and affect skeletal muscle, the cardiovascular system, pancreas, brain, gut and adipose tissue. Some of the adaptations related to cardiovascular fitness that have been discussed include those associated with increases in maximal oxygen consumption, such as higher hemoglobin mass, red blood cell volume, and cardiac output. In addition, adaptations such as increased mitochondrial function and capillary density that occur within the musculature were also discussed.
Other adaptations included in the review are the expansion and remodeling of the heart after long-term intense exercise and changes in the peripheral vasculature. The review also covered variations in cardiac hypertrophy patterns based on whether exercise training consisted of more endurance or resistance training.
Adaptations associated with skeletal muscle include increased capacity for aerobic energy production, capacity for carbohydrate oxidation, and higher mitochondrial biogenesis. A higher capacity for force generation, an increase in the cross-sectional area of muscle fibers through the accumulation of myofibrillar protein, and a greater capacity for non-oxidative energy production are some of the other adaptations in skeletal muscle associated with resistance exercise.
The review also extensively discussed resistance and endurance exercise adaptations in adipose tissue metabolism, liver function and pancreatic metabolism involving β cells. Changes in gut microbiota and brain function due to chronic exercise and their impact on overall health and reducing the risk of various diseases were also addressed in the review.
Final insights
Overall, the review comprehensively summarizes current knowledge on different types of chronic exercise regimens, such as endurance and resistance training, and the physiological and biochemical adaptations to exercise training that contribute to improved health and reduced disease risk.
