You are a strong cyclist. FTP is solid, you can ride four hours without fading, and your VO2max — tested or estimated — puts you in the upper tier for your age group. Then a friend talks you into a 5K. You finish with a heart rate of 155 and legs that feel like they have been beaten with sticks, at a pace that embarrasses you. A 13-year-old in cotton shorts beat you by two minutes.
What happened?
You just experienced the difference between central and peripheral fitness transfer — the most misunderstood aspect of cross-training in endurance sport. Your cardiovascular system transferred beautifully. Everything below the waist did not.
What the Menges review actually found
The 2026 systematic review by Menges et al., published in Frontiers in Sports and Active Living, synthesised the available research on cross-training between running and cycling. The central finding was clear: VO2max improvements gained through one modality transfer meaningfully to the other.
This was not a surprise to exercise physiologists — the concept of central cardiovascular adaptation being mode-independent has been established since the 1970s. But the Menges review provided a contemporary, systematic confirmation with a wider evidence base than previous reviews.
VO2max is determined primarily by three central factors: cardiac output (how much blood the heart pumps per minute), oxygen extraction (how efficiently the muscles pull oxygen from the blood), and plasma volume (the total blood volume available for circulation). All three respond to sustained elevated heart rate regardless of what movement pattern produces it. A cyclist doing 40 minutes at 75% of max heart rate and a runner doing 40 minutes at 75% of max heart rate are providing approximately the same stimulus to the central cardiovascular system.
The review also noted what does not transfer: peripheral, movement-specific adaptations. Running economy (how efficiently you convert oxygen into forward motion while running), eccentric force tolerance (the ability to absorb ground reaction forces without tissue damage), and the neuromuscular coordination patterns specific to running gait — none of these transfer from cycling. Similarly, pedalling economy, sustained power production in a fixed cycling position, and quadriceps-specific fatigue resistance do not transfer from running.
The practical summary: your aerobic engine is portable. Your movement skills and structural conditioning are not.
Central versus peripheral: the framework that explains everything
Understanding fitness transfer requires one distinction: central adaptations versus peripheral adaptations.
Central adaptations happen above the muscle. The heart gets bigger and stronger (increased stroke volume). The blood volume expands (more plasma, more haemoglobin). The capillary network in the muscles becomes denser. Mitochondrial density increases. These adaptations serve any activity that demands sustained oxygen delivery — cycling, running, swimming, rowing, cross-country skiing. They are the engine.
Peripheral adaptations happen within the specific muscles and connective tissues used by a particular movement. For cycling: quadriceps endurance, hamstring-to-quad force ratios optimised for the pedal stroke, tendon stiffness calibrated for concentric loading, neural drive patterns that coordinate 90-100 rpm pedalling. For running: Achilles tendon elasticity, plantar fascia resilience, calf force production during push-off, hip stabiliser activation during single-leg stance, and the stretch-shortening cycle that makes running metabolically efficient. These are the drivetrain — specific to each vehicle.
A strong cyclist has a powerful engine (high VO2max, large cardiac output, excellent oxygen extraction) bolted to a cycling-specific drivetrain (efficient pedalling, strong quads, adapted cycling tendons). When that cyclist starts running, the engine transfers — heart rate control, breathing patterns, aerobic efficiency are all present. The drivetrain does not. The running-specific muscles, tendons, and coordination patterns have to be built from scratch.
This is why fit cyclists get injured when they start running. The engine says "this pace is comfortable, let's go faster." The Achilles tendon, experiencing ground reaction forces of 6-8x body weight for the first time, says nothing — until it becomes inflamed three weeks later. The injury prevention guide exists specifically because of this central-peripheral gap.
The metabolic crossover
Beyond VO2max, there is a metabolic dimension to fitness transfer that is often overlooked.
Cyclists develop exceptional fat oxidation capacity — the ability to burn fat as fuel at moderate to moderately high intensities. This is a central metabolic adaptation driven by mitochondrial density and enzyme activity, and it transfers well to running. A cyclist who has trained their body to oxidise 0.8-1.0 g/min of fat during cycling will have similar fat oxidation rates during running at equivalent relative intensity.
This matters for endurance. Fat is an almost unlimited fuel source, while glycogen is limited. A cyclist with excellent fat oxidation can sustain moderate running for longer before bonking than a running-specific athlete with the same VO2max but less metabolic training.
The lactate threshold also transfers partially. The absolute speed or power at which lactate accumulates is mode-specific (you will hit threshold at a different running pace than your threshold cycling power would predict). But the physiological machinery that clears lactate — the monocarboxylate transporters, the oxidative enzyme systems, the liver's gluconeogenic capacity — transfers across modalities. A cyclist with a high lactate threshold on the bike will have a relatively high lactate threshold when running, even before doing any running-specific threshold work.
The implication: if you are a well-trained cyclist starting to run, your aerobic economy will be better than your running pace suggests. You are not as bad at running as your times make you look — you are bottlenecked by peripheral factors (running economy, structural tolerance), not by cardiovascular or metabolic capacity.
Why your heart is ready but your legs are not
The central-peripheral mismatch is the defining challenge of cross-training transfer, and it cuts both directions.
Cyclist to runner. Your resting heart rate is 48. Your cardiac output is well above average. Your body can deliver oxygen to working muscles at rates that support sustained moderate running from day one. But your calf muscles have never produced force against the ground. Your Achilles tendons have never absorbed eccentric loading. Your hip stabilisers have not been required to support a single-leg stance 180 times per minute. Your tibial periosteum has never been stressed by impact forces.
Result: you can run at a comfortable heart rate for 30 minutes while your musculoskeletal system accumulates damage it cannot signal until 48-72 hours later. The DOMS that follows a cyclist's first run is legendary — calves, hip flexors, glutes, and often the anterior tibialis are affected in a pattern distinct from anything cycling produces. The first 5K plan is structured specifically to manage this gap.
Runner to cyclist. The mirror image exists but is less dangerous. A runner who starts cycling has the cardiovascular fitness to sustain two to three hours on the bike, but their cycling-specific muscular endurance is absent. They fatigue in the quads and lower back before their heart rate reaches a meaningful training zone. The difference is that cycling does not produce eccentric damage — it is a concentric, non-impact activity — so the runner's structural risk is low. They will be slow and uncomfortable, but they will not get injured the way a cyclist starting to run will.
This asymmetry is why the transfer discussion matters more for cyclists considering running than for runners considering cycling. The consequences of overestimating your readiness are structurally different.
The numbers: what to expect
If you are a cyclist starting to run, here is a realistic calibration of what transfers and what does not.
VO2max. Your cycling VO2max (measured or estimated on the bike) will be approximately 5-15% higher than your running VO2max when measured on a treadmill, even with an established running background. For a cyclist with no running history, the gap may be larger initially (15-20%) and narrow to 5-10% over two to three months as running economy improves. A cyclist with a cycling VO2max of 58 ml/kg/min might test 50-53 ml/kg/min on a treadmill in the first month of running.
Heart rate. Your aerobic heart rate zones transfer directly. If Zone 2 on the bike is 125-145 bpm, Zone 2 running will be in a similar range. The difference is that you will run much slower at those heart rates than you expect — possibly 6:30-7:00/km when your ego tells you that you should be running 5:00/km. Trust the heart rate, not the pace.
Perceived effort. A moderate cycling effort (RPE 4-5 out of 10) will feel like RPE 3-4 cardiovascularly and RPE 6-7 muscularly when running at the same relative intensity. Your breathing is relaxed, your legs are in distress. This mismatch persists for six to eight weeks until running-specific muscular adaptation catches up.
Recovery. Cycling recovery patterns do not predict running recovery patterns. You may ride 90 minutes and feel fresh the next day. A 25-minute easy run may produce DOMS that lasts 72 hours. The eccentric component of running — muscles lengthening under load during the braking phase of each stride — creates tissue damage that cycling does not, and your recovery systems are not calibrated for it.
Practical implications for cyclists who run
The transfer research leads to several specific conclusions for cyclists adding running to their programmes.
Start absurdly slow. Your heart will tell you the pace is too easy. It is not. Your tissues need time to adapt to forces they have never experienced. Four to six weeks of easy run-walk sessions, as outlined in the first 5K guide, builds the peripheral foundation that lets you eventually run at paces your cardiovascular fitness can support.
Do not chase running VO2max improvement. Your VO2max is already high from cycling. Running does not need to push it higher — it needs to build the structural capacity to express the VO2max you already have. Running intervals before you have eight to twelve weeks of progressive easy running behind you is a shortcut to the physiotherapist.
Use cycling recovery protocols, but add eccentric tolerance. Your nutrition, sleep, and hydration practices from cycling apply. But add awareness of eccentric loading: downhill running produces substantially more tissue damage than flat or uphill running, trail running on uneven surfaces distributes forces across more tissues (which is good), and consecutive days of running for a new runner is more risky than consecutive days of cycling.
Expect the transfer to improve over time. The gap between your cardiovascular fitness and your running ability narrows as peripheral adaptations accumulate. After three to four months of consistent running (two to three times per week), most cyclists report that running starts to feel proportional to their overall fitness level. After six months, the central-peripheral gap is largely closed for easy and moderate intensities.
The reverse transfer protects your cycling. Running during the off-season preserves VO2max while cycling volume drops. When you return to structured riding, the central fitness is intact — you are rebuilding cycling-specific economy, not the entire aerobic engine. This shortens the time needed to return to peak cycling performance by several weeks compared to an off-season of reduced activity without running.
What the research does not tell you
The Menges review and the broader transfer literature have limitations worth noting.
Most studies examined relatively short intervention periods (4-12 weeks) in moderately trained participants. The long-term transfer dynamics for well-trained athletes — the population most readers of this site represent — are less well characterised. Anecdotal evidence from WorldTour riders who run year-round (Roglič, Evenepoel, Van Aert) suggests that transfer remains positive at high fitness levels, but the controlled data is thin.
The research also does not distinguish well between transfer of capacity (VO2max) and transfer of performance (race times, sustained power). You can have a high VO2max that transfers and still perform poorly in a new modality because economy — the metabolic cost of moving at a given speed — takes months to optimise. The cyclist who can sustain 300 watts on the bike has a VO2max that should support a fast 5K, but their running economy means that VO2max gets expressed as a mediocre time rather than a competitive one.
Accept this. The fitness is there, even when the performance does not reflect it yet. The gap closes with consistent practice, not by pushing harder.
More on building running into a structured cycling week without overtraining: the weekly scheduling guide.
If you want to work through the transfer calculation for your specific fitness level and plan running around your riding, the Roadman community on Skool is where that gets figured out.