Although the health benefits of exercise are indisputable, the cellular and molecular mechanisms are not fully understood. In addition, the extent to which these mechanisms differ among different types of exercise and in different populations (e.g., younger and older) remains unclear. A recent study by Robinson and others in Cell Metabolism examined the molecular changes taking place in young and older adults after conducting different forms of exercise: Resistance Training, High Intensity Interval Training, and Combined Training.
The Takehome: The different training modalities all improved markers for health and fitness, but in slightly different ways. High Intensity Training yielded the greatest changes, improving cardio-respiratory fitness, insulin sensitivity, mitochondrial respiration and fat-free mass in both young and older groups. Resistance Training improved fat-free mass, leg strength and insulin sensitivity in both age groups. This is an important point as most people believe metabolic parameters cannot be improved without metabolic conditioning (aerobic/anaerobic training). Here we see that in both young and older individuals, insulin sensitivity can be improved with resistance training. Combined training (which was actually aerobic training and lower volume strength training) improved cardio-respiratory fitness, fat-free mass and leg strength in both age groups, but only improved insulin sensitivity and mitochondrial respiration in the younger age group. Since this “combined group” was not a simple combination of the two other groups, it is unclear if this decrease in effectiveness in the older group resulted from a switch to aerobic training, the reduction in resistance training volume or a combination of the two. At the molecular level, High Intensity Training resulted in the greatest changes of gene and protein expression in both young and older individuals, particularly for genes associated with mitochondrial function (the energy powerhouse of the cell). Gene expression differences resulting from Resistance Training and Combined training were less numerous than for High Intensity Training and were more prominent in older adults than younger adults. Further studies will be needed to explain the significance of these different gene expression changes in the two age groups, particularly given that one or more changes at the molecular level seldom lead to straight-forward cause and effect behaviors.
- Two age groups were studied. Young (18-30 years) and Older (65-80).
- Both groups were relatively evenly balanced with males and females.
- Three exercise modalities were assessed: High Intensity Interval Training (HIIT), Resistance Training (RT) and Combined Training (CT).
- HIIT consisted of 3 days/week on a cycle ergometer with 4 cycles of 4 min high intensity (>90%) and 3 min active rest (light pedaling).
- RT consisted of numerous machine and free weight exercises performed within 60 minutes 4 days/week. Mon and Thurs were the lower body days. Tues and Fri were the upper body days. Total sets increased in number from 2 to 4 over the course of the study and repetitions were in the 8-12 range.
- CT was actually not a combination of the two prior modalities. It consisted of 30 minutes of cycling at 70% of each participant’s VO2max 5 days a week and a RT program similar to the RT group above, but with fewer exercises.
- The exercise/training period was 12 weeks and measurements were taken 72 hours after the last training session.
- HIIT training improved cardio-respiratory fitness, insulin sensitivity, mitochondrial respiration and fat-free mass in both young and older groups.
- RT improved fat-free mass, leg strength and insulin sensitivity in both age groups.
- CT improved cardio-respiratory fitness, fat-free mass and leg strength in both age groups, but only improved insulin sensitivity and mitochondrial respiration in the younger age group.
- Only HIIT improved aerobic capacity.
- HIIT resulted in the largest gene expression changes regardless of age.
- In older adults, HIIT resulted in greater gene expression changes than RT and CT.
- 11 genes that were down regulated with age were upregulated after HIIT training in older adults.
- Only HIIT increased mitochondrial protein synthesis in both younger and older participants.
- RT and CT produced increases in mitochondrial protein levels in older groups only.
- Training history of the participants was not assessed.
- Combined training was actually a different type of training. Instead of combining HIIT training with RT, the authors directed participants to perform aerobic training 5 days per week and the resistance training they did in combination was of a lower volume than found in the RT group.
- Because the CT group was a different stimulus althogether, we cannot say if the reduced effectiveness of this modality (particularly in older adults) is due to the switch to aerobic training, the reduction in resistance training volume or the combination of the two.
- Just because genes are upregulated, doesn’t mean that the upregulation of those genes has beneficial effects on health.