Individual physiological and mitochondrial responses during 12 weeks of intensified exercise, 2021, Jacques et al

Abstract

Aim
Observed effects of exercise are highly variable between individuals, and subject-by-training interaction (i.e., individual response variability) is often not estimated. Here, we measured mitochondrial (citrate synthetase, cytochrome-c oxidase, succinate dehydrogenase, and mitochondrial copy-number), performance markers (Wpeak, lactate threshold [LT], and VO2peak), and fiber type proportions/expression (type I, type IIa, and type IIx) in multiple time points during 12-week of high-intensity interval training (HIIT) to investigate effects of exercise at the individual level.

Methods
Sixteen young (age: 33.1 ± 9.0 years), healthy men (VO2peak 35–60 ml/min/kg and BMI: 26.4 ± 4.2) from the Gene SMART study completed 12-week of progressive HIIT. Performance markers and muscle biopsies were collected every 4 weeks. We used mixed-models and bivariate growth models to quantify individual response and to estimate correlations between variables.

Results
All performance markers exhibited significant (Wpeak 0.56 ± 0.33 p = 0.003, LT 0.37 ± 0.35 p = 0.007, VO2peak 3.81 ± 6.13 p = 0.02) increases overtime, with subject-by-training interaction being present (95% CI: Wpeak 0.09–0.24, LT 0.06–0.18, VO2peak 0.27–2.32). All other measurements did not exhibit significant changes. Fiber type IIa proportions at baseline was significantly associated with all physiological variables (p < 0.05), and citrate synthetase and cytochrome-c oxidase levels at baseline and overtime (i.e., intercept and slope) presented significant covariance (p < 0.05). Finally, low correlations between performance and mitochondrial markers were observed.

Conclusion
We identified a significant subject-by-training interaction for the performance markers. While for all other measures within-subject variability was too large and interindividual differences in training efficacy could not be verified. Changes in measurements in response to exercise were not correlated, and such disconnection should be further investigated by future studies.

Open access, https://physoc.onlinelibrary.wiley.com/doi/10.14814/phy2.14962

 

Notably, of the ~8% increase in VO2Peak, most of it was in the first 4 weeks.

The lack of a clear effect on mitochondrial or muscle fibre composition should not be too surprising. VO2Peak is rate-limited by the cardiovascular system - it is about how much oxygen can be delivered to the muscles. On the contrary to popular belief, there is still mitochondrial oxidative capacity left in the muscle, even at VO2Max.

It is disappointing that they didn't report blood pressure and heart rate during the test, so we could see how much of the increased VO2Peak is due to changes in those parameters.

I am more interested in changes in blood flow / capacity of the capillary system in the muscles over time, as VO2Peak increases, but they didn't measure that.

 

It also seems to say that we are not born equal when it comes to exercise so the gym teacher should have not been so sarcastic to those of us who tried but failed

 

didn't read the study, but did any of the subjects have their variables worsened by exercise? that would be interesting

 

All of the data was pooled into means, so we don't know. The SDs didn't really increase, so probably not in most participants, which is to be expected of healthy people.

 

With modern day computers you'd think it would not be difficult to make a graph of actual data points. Pooled data can give a shorthand answer but unless you see the spread of responses it is impossible to truly understand findings.

 

In the olden days they were worried about taking up too much space in the journal. These days that does not matter at all and researchers that don't provide basic data visualisations are simply inferior scientists...