# Blood Lactate Concentration Is Not Related to the Increase in Cardiorespiratory Fitness Induced by High Intensity Interval Training

PMID: 31395812
Journal: International journal of environmental research and public health
Published: 2019 Aug 9
Authors: Astorino TA, DeRevere JL, Anderson T, Kellogg E, Holstrom P, Ring S, Ghaseb N

## Question

Are blood lactate response, sleep duration, energy intake, or training heart rate associated with VO2max improvement after a brief HIIT program?

## Summary

In 14 already active adults, 3 weeks of cycling HIIT improved VO2max by about 6%. Blood lactate response, energy intake, and sleep duration did not predict the VO2max change, but higher training heart rate was associated with larger improvements.

## Population

- Recreationally active adults recruited by convenience sampling
- Sample size: 14
- Age: 27 +/- 8 years
- Sex: 3 men, 11 women
- Fitness level: Performed >150 min/week of exercise in the last 12 months; VO2max 38 +/- 4 mL/kg/min
- Health status: Apparently healthy adults based on health-history questionnaire

## Methodology

- Single-group pre-post training study
- 3 weeks
- Laboratory cycle ergometer training and testing

## Protocol

- Ventilatory-threshold based HIIT.
- Modality: Electrically braked cycle ergometer.
- Work intervals: 1 min at 130% ventilatory threshold.
- Recovery: 75 s active recovery at 10% peak power output.
- Sets or repetitions: 8 intervals in sessions 1-3, 9 in sessions 4-6, 10 in sessions 7-9.
- Intensity: 130% ventilatory threshold, equal to about 70% peak power output; elicited about 90% +/- 5% PPO and 95% +/- 3% HRmax.
- Session duration: 5 min warm-up plus intervals and recoveries.
- Frequency: 3 sessions/week.
- Program length: 3 weeks.
- Progression: Intervals increased from 8 to 9 to 10 across each 3-session block.
- No comparator.

## Outcomes

### VO2max
Status: improved
VO2max increased after nine HIIT sessions.

p = 0.007; +6%; +0.15 +/- 0.13 L/min and +2.4 +/- 1.8 mL/kg/min

### Blood lactate
Status: no clear change
Blood lactate response did not predict VO2max improvement.

Delta VO2max vs BLa r = 0.44, p = 0.10; mean BLa day 1 r = 0.17, p = 0.57; day 9 r = 0.48, p = 0.08

### Sleep
Status: no clear change
Sleep duration was not associated with VO2max change.

r = 0.14, p = 0.62

### Energy intake
Status: no clear change
Energy intake was not associated with VO2max change.

r = 0.38, p = 0.18; intake 2050 +/- 686 to 2074 +/- 639 kcal, p = 0.39

### Heart rate
Status: improved
Higher training heart rate was associated with larger VO2max improvement.

r = 0.62, p = 0.02; mean training HR 95% +/- 3% HRmax

## Practical Insights

- A brief 3-week HIIT block can improve VO2max even in already active adults.
- Heart-rate response may be a more useful training signal than lactate for predicting VO2max response in this protocol.
- The study is not evidence that lactate is irrelevant in all HIIT programs; it used threshold-based cycling in a small sample.

## Limitations

- No control group
- Small sample
- Active participants rather than sedentary users
- Self-reported diet and sleep
- Brief training duration
- Underpowered for sex-specific effects

## Safety And Adherence

- No adverse-event reporting was identified in the extracted text; participants were apparently healthy and exercised in the lab.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/31395812/) (pubmed)
- [DOI](https://doi.org/10.3390/ijerph16162845) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6720831/) (full text)

## Agent Guidance

Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.