Physiology basics
How the body works, as the reviews agree.
Energy and intensity
Is a 3-minute interval anaerobic?Mostly not. All three energy systems work at once, and even in an all-out effort the aerobic share passes half at about 75-80 seconds by most estimates, so a 3-minute rep is mostly aerobic.
Is Zone 2 the fat-burning zone?Partly. Fat oxidation peaks at a moderate intensity, at a point that differs between people, and harder work runs more on carbohydrate.
But burning more fat during a ride is not losing more body fat.
Read PHYS-02 in full →Do I need to flush out lactic acid so I am not sore tomorrow?No. Lactate is a fuel your body clears on its own; next-day soreness follows new or eccentric work.
An easy cool-down clears blood lactate faster but did not ease soreness.
Read PHYS-06 in full →What is critical power, and why do reps above it end so quickly?It approximates the top of the heavy domain. Below it the body can settle; above it VO2 climbs to its maximum and a limited reserve runs down, so the effort soon ends.
My heart rate never reaches the zone in 1-minute reps. Was the rep too easy?Heart rate cannot say. Oxygen uptake and heart rate lag a change in work, so a short rep ends before they arrive.
Judge it by power, pace or effort.
Read PHYS-08 in full →Heart, blood and oxygen
How do I raise my VO2max, and what limits it?Mostly the heart and blood. VO2max is cardiac output times the oxygen the muscles take out, and training raises it chiefly through a bigger stroke volume, more plasma and more haemoglobin.
Why is my friend faster with a lower VO2max?VO2max is only the ceiling. Speed also depends on how much of it you can hold for the race, how much speed each litre of oxygen buys, and how well those hold late in a long effort.well supported
Are my lungs my limiter, and is hard training at −10 °C bad for them?Rarely the lungs, unless you are highly trained. Cold, dry air can narrow the airways of those prone to it; wheeze or a tight chest then is for a doctor.well supported
After a week of heat training my heart rate is lower at the same pace. Am I fitter?Partly it is more blood: plasma expands within days of heat or new training, so the heart fills better and beats slower.
Weeks off shrink it again.
Read PHYS-13 in full →Why does my heart rate creep up on long rides at the same watts?That is cardiovascular drift: after about 10 minutes heart rate rises as stroke volume falls.
Heat and fluid loss make it bigger, and with them the effort really does get harder.
Read PHYS-11 in full →My heart rate hit 183 at 44, above 220 minus age. Is that a problem?Not on its own. Age formulas give a group average and missed endurance athletes by about 10 bpm either way in a large study, so a measured maximum above the formula is ordinary variation.
Muscle and strength
Do low-cadence intervals train my fast-twitch fibres?Fibres join small to large as force rises, so high torque brings in more.
Whether low cadence at equal power does is unsettled; low-cadence training gave no clear extra gain.
Read PHYS-16 in full →I'm fast-twitch. Am I not built for endurance?The mix is partly inherited and varies widely, but training turns fast fibres toward the fatigue-resistant IIa type; slow-fast conversion is debated.
Train the event, not the label.
Read PHYS-17 in full →Will lifting make me bulky?Not quickly. The first weeks' strength gains come mostly from the nervous system learning to drive the muscle; growth follows later and slowly, and heavy lifting improved endurance athletes' economy.well supported
Do I need a protein shake within 30 minutes of lifting?No. In meta-analyses the day's protein total, with the training, decided the gain; timing added nothing once total intake was counted.well supported
Older muscle needs bigger doses.
Read PHYS-21 in full →Do heavy squats boost testosterone and build more muscle?Hard sessions raise testosterone, growth hormone and cortisol for minutes, but in trials the size of the rise did not predict gains, and the cortisol rise is normal, not harm.contested
Will my running or riding hurt my strength gains?A little, mostly for explosive power: in meta-analyses maximal strength and muscle size were largely spared, and the power loss sat mostly in same-session designs.well supported
Training and adaptation
Does one big session build fitness, or the weeks of them?The weeks. Each session sends a brief molecular signal; mitochondria and capillaries grow from repeated sessions with recovery between, and both volume and intensity count.
Same rides every week and my FTP is stuck. Why?Partly because the body adapts to what it meets: a familiar load moves fitness less, and the fitter gain less from any step.
Raise one thing (minutes, density or target), and recover.
Read PHYS-39 in full →Does running help my cycling, or hiking my running?Partly. The shared heart-and-blood part transfers; threshold and muscle gains stay with the sport trained.
One trial: extra swimming gave runners half the gain of extra running.
Read PHYS-40 in full →How much fitness do I lose on a two-week holiday?A little. In trained athletes who stopped completely, VO2max was a few per cent lower after two to three weeks, much of it lost blood volume, and strength held longer.
Same plan as my friend, much smaller gain. Am I a non-responder?One block cannot say. In trials of untrained adults most of the spread between people after one block was test noise, the less fit gained more, and flat results mostly moved with more training.well supported
My heart is fit but my Achilles hurts six weeks into running. Why?Fitness can rise while the tendon stays unchanged: tendon stiffens under high strain over weeks to months of loading, and its core barely renews.
Ramp running by the tendon, not by how easy it feels.
Read PHYS-38 in full →Cyclist: is my bone density at risk, and do jumps help?It may be: road cyclists often have low density, and bone builds from impact and heavy loads, not riding hours.
Jumps and lifting look promising for cyclists, not yet proven.
Read PHYS-37 in full →Damage, fatigue and recovery
Why are my legs wrecked after a trail race but fine after five hours on the bike?Running, above all downhill, lengthens working muscle under load, which damages it; pedalling is mostly shortening work.
Strain, not effort, decides.
Read PHYS-22 in full →Why am I most sore two days later, not the same evening?After new or downhill work soreness typically starts 12-24 h later, peaks at 24-72 h, while fibre damage is still spreading, and is gone within 5-7 days; strength can stay down after it fades.
My first downhill runs left me wrecked. Will it always be like that?No. One bout of eccentric work protects the muscle against the next, so damage and soreness drop quickly with repetition.
Tendons adapt far more slowly, over months.
Read PHYS-24 in full →My CK was high after a race. Is something wrong, or am I not recovered?A rise after a long, hard or downhill effort is expected and falls back over days.
Its size says as much about you as about the race, and not when you are ready.
Read PHYS-25 in full →How long do I need to recover after a hard session?It depends on what it cost: after brief intense work force returns within minutes to hours, longer after heavy or long sessions; glycogen takes about a day, eccentric damage days.well supported
My HRV dropped after a hard block. Am I overtrained?Unlikely from that alone. A dip that rebounds with rest is normal; overtraining is a lasting performance drop found by ruling out other causes, and HRV did not reflect overreaching.
Will more sleep help my legs? How much do I need?Lost sleep lowers next-day performance, most clearly after a sleepless night or an early wake-up.
Need is individual, with no fixed target for all; many athletes sleep under 7 h.
Read PHYS-34 in full →Do hard races and big blocks make me ill?They may add risk. Infections in athletes go with heavy load, competition, travel and poor sleep; whether one hard session opens a window is disputed.contested
Regular exercise goes with fewer colds.
Read PHYS-35 in full →Fuel, iron and energy balance
Will fasted rides or Zone 2 make me leaner?Not by themselves. They burn more fat during the ride, but body fat follows energy eaten and spent over days and weeks; fasted against fed exercise made a trivial difference to body mass.
Do I need to carb-load for a 10 km or a one-hour race?No. Loading helped only in events longer than about 90 minutes; in shorter races the muscles finish with glycogen to spare, so normal high-carbohydrate eating is enough.well supported
Do I have to eat straight after training?Only when the next hard session is within hours. Storage is fastest right after exercise, but with enough carbohydrate over the day the muscle refills within about a day either way.
My period stopped while I was losing weight. Is that just hard training?Probably not. When food falls short of what training uses, the body turns down reproduction, metabolism and bone, in men too.
Fuel up and see a sports doctor.
Read PHYS-32 in full →Always tired, ferritin 28: could it be iron?It could. Athletes lose iron and may absorb less after hard sessions; whether low stores without anaemia slow you is disputed, and inflammation raises ferritin.
Test before supplementing.
Read PHYS-36 in full →Heat, altitude and fluids
Why is my heart rate 15 beats higher in the heat at the same pace?Blood flow to hot skin and sweating strain the heart and heat shrinks your aerobic reserve, so the same pace is a harder effort, not noise or lost fitness.
How long does it take to adapt to the heat?Most of it comes in one to two weeks of exercising in the heat: heart rate and core temperature run lower at the same work, sweating rises.
Without heat it fades over weeks; people differ.
Read PHYS-29 in full →Why do I sweat so much more than my friend?Sweat rate and its salt content vary widely between people, even in one sport, and with heat and effort.
It is cooling, not fat burned (aerobic training and heat acclimation raise it); weigh before and after a ride for yours.
Read PHYS-30 in full →Do I cramp because I need more salt?Probably not, for most. The evidence leans to fatigue upsetting the nerve signals to the muscle; salt or fluid loss may play a part in some cases, and past cramps are the clearest predictor.contested
How much slower will I be at 2000 m?Noticeably in anything aerobic. Thinner air lowers VO2max, more the higher you go and often more in the highly trained; two weeks there may win back about half.
Pace by effort, not sea-level power.
Read PHYS-14 in full →Tests, markers and wearables
My FTP went from 248 to 253. Did I improve?Maybe not. Even a lab power test carries about 1-2% noise, and two readings differ by more than that by chance, so one 2% rise is compatible with no change.
Repeat the same test.
Read PHYS-43 in full →My HRV crashed and my CK is high. Am I overtrained?Not from those alone. Each marker has its own causes and noise (alcohol, a late session, a race), and none diagnoses overtraining.
Read trends beside how you feel and perform.
Read PHYS-44 in full →My sRPE and TSS disagree. Which is wrong?Probably neither. TSS counts the work against a stored threshold; sRPE is what it cost you.
Heat, mental fatigue, overreaching or a stale threshold pull them apart: the gap is a question.
Read PHYS-45 in full →Smart scale: body fat up 2% overnight. Real?No. It measures resistance to a current and estimates fat by equation; a change can be missed by several points, so 2% is noise.well supported
Watch calories, sleep stages and VO2max are estimates.
Read PHYS-46 in full →Pros ride 25 h a week and have huge VO2max. Should I copy them?Not on that basis. What separates elites from amateurs does not show what will change you; a comparison of people cannot see training.well supported
Your own records steer.
Read PHYS-47 in full →