The Salzburg 10/7 HIIT shock cycle study: the effects of a 7-day high-intensity interval training shock microcycle with or without additional low-intensity training on endurance performance, well-being, stress and recovery in endurance trained athletes-study protocol of a randomized controlled trial

Abstract

Background: Performing multiple high-intensity interval training (HIIT) sessions in a compressed period of time (approximately 7-14 days) is called a HIIT shock microcycle (SM) and promises a rapid increase in endurance performance. However, the efficacy of HIIT-SM, as well as knowledge about optimal training volumes during a SM in the endurance-trained population have not been adequately investigated. This study aims to examine the effects of two different types of HIIT-SM (with or without additional low-intensity training (LIT)) compared to a control group (CG) on key endurance performance variables. Moreover, participants are closely monitored for stress, fatigue, recovery, and sleep before, during and after the intervention using innovative biomarkers, questionnaires, and wearable devices.

Methods: This is a study protocol of a randomized controlled trial that includes the results of a pilot participant. Thirty-six endurance trained athletes will be recruited and randomly assigned to either a HIIT-SM (HSM) group, HIIT-SM with additional LIT (HSM + LIT) group or a CG. All participants will be monitored before (9 days), during (7 days), and after (14 days) a 7-day intervention, for a total of 30 days. Participants in both intervention groups will complete 10 HIIT sessions over 7 consecutive days, with an additional 30 min of LIT in the HSM + LIT group. HIIT sessions consist of aerobic HIIT, i.e., 5 × 4 min at 90-95% of maximal heart rate interspersed by recovery periods of 2.5 min. To determine the effects of the intervention, physiological exercise testing, and a 5 km time trial will be conducted before and after the intervention.

Results: The feasibility study indicates good adherence and performance improvement of the pilot participant. Load monitoring tools, i.e., biomarkers and questionnaires showed increased values during the intervention period, indicating sensitive variables.

Conclusion: This study will be the first to examine the effects of different total training volumes of HIIT-SM, especially the combination of LIT and HIIT in the HSM + LIT group. In addition, different assessments to monitor the athletes' load during such an exhaustive training period will allow the identification of load monitoring tools such as innovative biomarkers, questionnaires, and wearable technology.

Trial registration: clinicaltrials.gov, NCT05067426. Registered 05 October 2021-Retrospectively registered, https://ichgcp.net/clinical-trials-registry/NCT05067426 . Protocol Version Issue date: 1 Dec 2021. Original protocol. Authors: TLS, NH.

Keywords: Block training; HIIT; HIT; Interval exercise; LIT; Load monitoring.

Conflict of interest statement

All authors declare no competing interests. Based on the scientific cooperation with no commercial interest, the study has received funding from the Red Bull Athlete Performance Center. The funding body has not peer-reviewed the manuscript. This sponsor was not involved in the study design, the writing of the manuscript, or the decision to submit the manuscript for publication.

© 2022. The Author(s).

Figures

Fig. 1

Study flowchart. The study is divided into a baseline period of 8–9 days (from T0 to T1), an intervention period of 7 days, and a post-intervention period of 14 days. Time points T0-T6 are face-to-face appointments for participants of all groups, with the HIIT sessions at T2 and T3 completed by the intervention groups, only

Fig. 2

Outline of the 7-day intervention period and an exemplary training session. Outline of the 7-day intervention period (above) and an exemplary training session (below). Red bars represent intense runs and intervals at 90–95% HRmax. Green bars represent warm-up, active recovery and 30 min LIT at a velocity at 1.5 mmol/L blood lactate. HIIT = high-intensity interval training, LIT = low-intensity training, HSM = high-intensity interval training shock microcycle, HSM + LIT = high-intensity interval training shock microcycle with additional low-intensity training, R = Rest, AM = morning, PM = afternoon, black runner = self-directed HIIT session, blue runner = supervised HIIT session

Fig. 3

Illustration of the incremental, sub-maximal test (above) and ramp test (below) including completion criteria of phase 1 and phase 2 characteristics. Bars represent the duration, running velocity, and treadmill grade of each stage. Blood drop = capillary blood collection, ♀ = starting velocity for female participants, ♂ = starting velocity for male participants, green circle = determined velocity for phase 2 determined in phase 1, RER = respiratory exchange rate, min = minutes. During the incremental test, stages are three minutes each with an increment of 1.5 km/h per step. The ramp test stages last 1 min with a 1.5% increase in slope after each stage

Fig. 4

Lactate threshold determination. An example of how LT (lactate threshold) is determined based on the results of the incremental test. v, treadmill running velocity in km/h; f = best fit regression function of blood lactate over treadmill velocity; La(v), blood lactate values at the treadmill velocity v in mmol/L

Fig. 5

Overview of selected monitoring variables. An overview of selected variables (y-axis; neuromuscular performance, well-being, CK, cfDNA) at time points (x-axis) at rest. The VAS (well-being) scores should be understood such that a higher score indicates a decrease in well-being. Biomarker monitoring in the present case was measured at selected time points during the intervention phase and will be extended to a daily assessment in the upcoming study