A breath-hold hypoxic training app called Redplus Performance is being trialled by professional cyclists across several WorldTour and ProTeam squads, according to internal records seen by Velora alongside an extended interview with the founder.
The system, marketed as "Altitude Training@Home," guides users through repeated empty-lung breath holds, while a Bluetooth-connected finger pulse oximeter tracks blood oxygen saturation (SpO₂) in real time.
Its founder, Danish entrepreneur and active competitive cyclist Niels Kristian Andersen, has been reaching out directly to coaches and team staff to introduce the system, and a growing list of riders are now actively testing it.
Velora has seen records confirming that the app is being used or trialled by riders across the WorldTour, ProTeam, Continental, junior and masters levels – though the identities of most individuals remain confidential. Redplus says beta testers include WorldTour cyclists, under-23 endurance athletes, elite endurance athletes and masters competitors, and that "one of our World Tour Cyclists was victorious in the early Spring of 2026."
The appeal for riders and coaches is an alternative to expensive and time-consuming altitude camps. A pocket-sized pulse oximeter and a phone app that can be used in a hotel room, an airport or at home offers a more convenient and lower cost alternative with measurable session data.
The system did not emerge from a marketing exercise. Andersen, a former and still-active competitive cyclist, developed the protocol through nine months of structured self-testing, logging breath-hold sessions alongside blood tests taken on 18 December 2024, 21 January, 26 February and 18 March 2025. He told Velora those tests showed his haematocrit rising from 42.5 to 46.9 over the period, a result that prompted him to formalise the method, file patent applications and build the app around it. The work has since been scientifically reviewed by sports scientist and former pro cycling team coach Daniel Healey, although that review remains internal to the company.
Andersen described his route into professional cycling as direct and informal. He first contacted one WorldTour coach after seeing a social media post from an altitude camp, and sent a message. After an initial silence, a meeting followed and the team were soon testing the system. The same pattern followed for other teams. Redplus is open that as a system it still has limited blood & performance data validation.
The method has a documented founder case, a named junior case study, and structured internal testing behind it. But the jump from short-term biomarker signals and individual observations to durable performance gains in elite endurance athletes, demonstrated through controlled, published research, remains incomplete.
A public case study
The most developed external example Andersen offered is Magnus Haagensen, a Danish national junior who has completed the full Redplus protocol – roughly 12 weeks of build phase, four weeks of peak with twice-daily sessions, then a deacclimatisation period. Andersen said Haagensen finished his deacclimatisation last week and reported being able to hold 450 watts seated for 30-by-15 intervals, where he had previously struggled to sustain 420 watts, even while standing. Haagensen's coach, Martin Mortensen, has since asked to put additional riders onto the programme as the team prepares to move up to Continental level next year. Both Haagensen and Mortensen have agreed to discuss the work directly with Velora.
A single rider's training-block improvement does not isolate the breath-hold work from the rest of his preparation, and Andersen did not present blood data for Haagensen alongside the power numbers. The case sits as a concrete example of a form gain seen alongside the training protocol, albeit falling short of controlled environment evidence of the system's benefits.
The protocol used by Haagensen and other pros centres on exhaling fully, then holding one's breath for as long as comfortably tolerable, followed by a recovery period of normal breathing. This cycle is repeated 10 to 20 or more times per session, with each session lasting 15 to 30 minutes. The pulse oximeter feeds SpO₂ data to the app, which records hold duration, depth of desaturation and recovery speed.
Redplus claims that empty-lung breath holds force a rapid drop in arterial oxygen, reaching 70–80% SpO₂ in some users - far deeper than the 88–92% typically achieved by altitude masks or simulated-altitude rooms. The company says this deep, brief desaturation directly targets HIF-1α, the hypoxia-inducible factor at the centre of the body's oxygen-sensing pathway. When oxygen drops low enough, HIF-1α avoids its normal degradation cycle and triggers erythropoietin (EPO) production, the hormone that stimulates new red blood cell creation. More red blood cells means more oxygen-carrying capacity, which, in theory, means better endurance.
The app structures training into build, peak and deacclimatisation phases, estimates weekly red blood cell yield using an algorithm, and displays progress over time. Andersen argues that one of the app's practical advantages over earlier breath-hold research is that it allows repetition-by-repetition logging – SpO₂ depth, hold duration, session structure and compliance – to be tracked in real time, in a way that previous study designs have struggled with.
A coach-facing admin panel is still under development, something Andersen described as a "critical step" before wider release. He said one of the WorldTour coaches he speaks with had specifically raised the lack of coach-side data access as the main barrier to deeper team integration.
The science, and its limits
The physiological chain Redplus describes – from deep desaturation to HIF stabilisation to EPO release – draws on research recognised by the Nobel committee, Andersen explains. William Kaelin Jr., Peter Ratcliffe and Gregg Semenza shared the 2019 Nobel Prize in Physiology or Medicine for demonstrating how cells sense and adapt to oxygen availability.
A 2025 review in the European Journal of Applied Physiology confirmed that serial breath-holding interspersed with recovery to normal SpO₂ levels "has been shown to transiently elevate EPO concentrations" and noted favourable cardiorespiratory and cerebrovascular adaptations.
However, the same review identified remaining uncertainties. It called for "further placebo-controlled studies" and said the optimal protocol and duration remain unclear. An earlier meta-analysis from 2023 found intermittent hypoxic training did increase VO₂max and haemoglobin, but noted limited study quality.
The central evidence gap is on whether transient EPO spikes translate into race-relevant watts. Established altitude research suggests a 1% change in Hbmass is associated with a 0.6-0.7% change in VO₂max – according to a paper in the British Journal of Sports Medicine. Whether 15-30 minutes of daily breath holds can produce that 1% shift in a trained cyclist, and sustain it, is the question Redplus has not yet answered with published data.
Andersen acknowledged the evidence gap, but said the coaches he speaks with are willing to move ahead of formal validation. He quoted one of his contacts as telling him: "I believe in this and I don't have the time to wait for the science to be validated in two years."
Safety
The product remains in beta and coach oversight tools are incomplete but under development. Safety controls, including SpO₂ floor warnings, phone vibrations and session-stop triggers, are being built in, though Andersen acknowledged the SpO₂ low point often occurs after the breath hold ends, creating a lag between exposure and measurement.
Andersen also told Velora he has actively pushed back against riders treating sessions competitively. He recounted a conversation with one WorldTour rider who went particularly low in SpO₂ readings: "What do you feel when you do it?" Andersen recalled asking the rider. "And he said: 'I feel like I have drink 3 beers'. It was a very happy feeling. I said: 'okay. But I know that feeling – it is the altitude simulation in action you can feel. But it's not necessary to go down there, as it is equivalent to near to 10,000m of altitude'."
Andersen explained that he is now working on a stricter programme structure to discourage overreach.
Breath-hold practices carry inherent risk. Shallow-water blackout during underwater breath-holding has caused deaths, and Norwegian biathlete Sivert Bakken was found dead wearing a hypoxic training mask in 2025. Redplus's app-monitored protocol in a controlled setting does not carry the same specific dangers, but any practice that deliberately drops blood oxygen into the 70s carries risks.
Andersen said Redplus is in active discussions with at least one WorldTour team about deeper integration, and that the immediate development priority is the coach-facing admin panel. He said the company is also in talks with Vekta about a more integrated data pathway. The business model, he said, is a subscription-based app once the admin panel and safety mechanisms are complete.
As pro cycling continues through an era of exceptional and unprecedented physiological performances, Redplus may be among a number of novel training methods now being trialled by riders and teams.
Whether peer-reviewed validation ultimately follows remains uncertain, but among elite athletes the search for marginal gains rarely waits for scientific consensus.
Editorial note: Medical references reviewed by Dr Will Chaundy, MBBS BSc (Physiology and Pharmacology)
Cover image credit: Zac Williams/SWpix.com
