Scientific foundation

The metabolic cost of cycling is directly proportional to the mechanical work performed. With a cyclist's gross efficiency typically between 20% and 25%, total caloric expenditure can be approximated from average sustained power:

Of that total expenditure, the proportion fueled by carbohydrates versus fat depends on relative intensity (%FTP). At easy paces, the body primarily oxidizes fatty acids (30-50 g/h carbohydrate demand), whereas in Zone 3 Tempo (76-90% FTP) and Zone 4 Threshold (91-105% FTP), exogenous glucose demand rises to 60-90 g/h or up to 120 g/h using dual maltodextrin:fructose ratios (1:0.8) and gut training.

Glycogen dynamics & gastric delay. Glycogen stores do not change instantaneously upon ingestion: there is a physiological delay from gastric emptying and intestinal transport, with peak plasma absorption occurring approximately 25 minutes post-ingestion:

Metabolic phenotype (VLaMax). Maximum lactate production rate (VLaMax) modulates glycogen expenditure below 80% FTP:

Indoor trainer adjustment. Outdoors, 15% to 20% of ride time is spent at 0 W (descents, corners, traffic lights, drafting). On an indoor trainer with constant resistance (ERG mode or fixed flywheel inertia), pedaling is 100% continuous. To reflect this uninterrupted expenditure without micro-rests, the engine applies a 1.12× multiplier to glycogen consumption per hour.

Cf. Jeukendrup & Wallis (2005) on substrate oxidation; Coyle et al. (1991) on glycogen depletion and gastric absorption kinetics.

The intestinal epithelium features specialized transporters with finite rate capacity:

1. Standard Mode (SGLT1 saturated at 60 g/h). Relies exclusively on the sodium-coupled transporter SGLT1 (glucose/maltodextrin). Exceeding 60 g/h without fructose causes solute accumulation in the intestinal lumen, osmotic water draw, and gastrointestinal distress.

2. Advanced Mode (SGLT1 + GLUT5 Co-transport up to 90-120 g/h). By recruiting the passive GLUT5 pathway via fructose in dual ratios (2:1 to 1:0.8), SGLT1 saturation is bypassed, elevating the absorption ceiling to 90-120 g/h in athletes with Gut Training — but not just any fructose ratio activates this pathway sufficiently: the real ceiling unlocked by each ratio depends on what fraction of the mix is fructose, not just that it "contains some".

Fructose ratio validation (120 g/h ceiling). A 2:1 ratio (maltodextrin:fructose) provides only 33.3% fructose of total carbohydrates — insufficient to saturate GLUT5 enough to sustain 120 g/h, so this ratio is capped at 90 g/h regardless of whether the athlete has active Gut Training. A 1:0.8 ratio provides 44.4% fructose, exceeding the 35% threshold that adequately recruits the pathway — only this combination (active Gut Training and ratio ≥35% fructose) unlocks the 120 g/h ceiling.

Cf. Jeukendrup (2010) on multiple transportable carbohydrates; Jentjens & Jeukendrup (2005) on glucose:fructose co-transport.

Thermal stress dictates both fluid volume requirements and electrolyte concentration:

1. Standard mix vs heat mix:

2. Accelerated sip frequency. In warm conditions (≥25°C), recommended sip frequency accelerates to every 12 minutes to maintain continuous hydration flow and prevent acute dehydration without overwhelming gastric volume.

3. Indoor thermal stress from absent convection. Indoors, the lack of high-speed relative airflow (30-40 km/h) drastically reduces convective cooling, elevating core and skin temperatures. This increases estimated sweat rate by +18% compared to identical power outdoors.

4. Physiological ceiling of gastric emptying (1000 ml/h). The human stomach has a maximum gastric emptying rate of roughly 900-1000 ml/h during exercise. Ingesting higher volumes — even in extreme sweat conditions — causes gastric pooling and nausea. RATIO caps active on-bike fluid recommendations strictly at 1000 ml/h, shunting any remaining deficit to the post-ride rehydration protocol.

Cf. Sawka et al. (2007), ACSM Position Stand on exercise and fluid replacement; Baker (2017) on sodium variability.

The tactical planner applies metabolic opportunity rules based on GPX elevation profile:

1. Pre-Climb Priming. Fast-absorbing carbohydrate intake is scheduled 10 to 15 minutes before entering significant climbs (>4% gradient). If the transition between two consecutive climbs is under 5 minutes, intake is consolidated prior to the first climb.

2. Descents Lockout (Gradients <-3%). Solid food alerts are suppressed during steep descents (<-3%) for technical safety and due to reduced splanchnic blood flow during high-speed bike handling.

Cf. Pfeiffer et al. (2012) on nutritional intake during competition and tactical safety factors.

Sweat sodium concentration varies substantially between individuals — far more than sweat volume itself — and is largely genetic rather than trainable. A "salty sweater" (recognizable by white salt crusts on jerseys or eye stinging during efforts) can lose sodium at concentrations far above average; replenishing with a generic sports drink formulated for average sweaters leaves a cumulative deficit on long rides.

Under-dosing sodium in a genuine salty sweater, particularly on long, hot rides with high plain water intake, is a primary risk factor for exercise-associated hyponatremia (EAH) — an uncommon but potentially severe condition where plasma sodium is diluted below safe levels.

Osmotic tolerance limit in bidons. Sodium concentrations above 1100 mg Na+/L (>2.2g of E-volytes per 550ml bottle) invert the osmotic gradient in the intestinal lumen, drawing plasma water back into the gut. To prevent gastrointestinal upset and osmotic diarrhea, the planner warns whenever electrolyte density per bottle exceeds this safety threshold.

Cf. Baker (2017) on individual variability in sweat sodium concentration; Hew-Butler et al. (2015), international consensus on exercise-associated hyponatremia.

A bottle drink cannot be concentrated indefinitely to save volume: above a certain carbohydrate concentration, the solution becomes hypertonic relative to blood plasma, slowing gastric emptying and drawing water into the gut via osmosis rather than facilitating rapid absorption — the exact opposite of a performance beverage's goal.

The reference base formula — 24g maltodextrin + 20g fructose + 1.0g table salt dissolved in 550ml water — sits deliberately around 8% carbohydrate concentration, safely below the GI distress threshold and physical solubility limits, scaling proportionally to actual bottle size.

Mix ratio scales with target intake rate, not a static ratio. Below 45 g/h, the SGLT1 transporter (sodium-coupled) is not saturated, so adding fructose provides no extra absorption — pure maltodextrin suffices. Between 45 and 75 g/h, a 2:1 ratio (maltodextrin:fructose) begins recruiting the GLUT5 transporter (sodium-independent) to elevate absorption without excessive fructose load. Above 75 g/h — where SGLT1 alone is fully saturated — the ratio shifts to 1:0.8, identified by dual co-transport research as optimal for near-maximal combined absorption rates.

Caffeine timing. Caffeine reaches peak plasma concentration 30 to 60 minutes after oral ingestion, with well-documented ergogenic benefits on perceived exertion and neuromuscular recruitment in late stages of prolonged effort. Anchoring intake ~45 minutes prior to the most demanding segment — a late climb, or the final hour on flat terrain — maximizes plasma concentration right when needed most.

Cf. Jeukendrup (2004) on carbohydrate dosing models in sports drinks; Cook & Beaven (2013) on caffeine timing and endurance performance.

Muscle glycogen resynthesis does not proceed at a constant rate across the recovery window. The first 30-45 minutes post-exercise are physiologically unique: muscle glucose uptake occurs largely via contraction-induced GLUT-4 translocation, an insulin-independent mechanism far more efficient than at rest. Leveraging this window with fast-absorbing liquid carbohydrates accelerates resynthesis before this mechanism wanes.

Deliberate over-hydration (exceeding exact fluid lost) compensates for ongoing post-exercise sweat and urinary losses that persist after stopping — replenishing only exact loss leaves the athlete in net negative balance hours later.

Protein and fat limits in the recovery window do not scale with calories burned on-bike: they serve muscle tissue repair and rapid gastric emptying, not a measured caloric deficit.

Cf. Ivy & Kuo (1998) on GLUT-4 role in post-exercise resynthesis; Beelen et al. (2010) on nutritional recovery strategies in cycling; Shirreffs & Sawka (2011) on post-exercise rehydration.

This section documents an ongoing refinement to section 01·'s energy model — currently in validation phase, not yet reflected in live planner calculations — that isolates aerodynamic draft savings by terrain and peloton position, modeling how mechanical efficiency degrades over long durations.

1. Aerodynamic draft savings by terrain & position. Drafting saves substantially more energy on flats — where aerodynamic drag dominates total resistance at speed — than on climbs, where body weight outweighs drag and residual savings are minimal.

2. Gross mechanical efficiency degradation after hour 3. Conversion efficiency of chemical energy to mechanical work (~22% baseline, see section 01·) is not constant in long events: muscular fatigue and progressive recruitment of less efficient fibers reduce it at −1.5% per additional hour past hour three, with an 18% floor.

Cf. Hausswirth et al. (1999) on energy cost of drafting; Cejuela & Esteve-Lanao (2011/2020) on endurance training load quantification.

A second ongoing refinement, also pending live planner integration, extends section 03·'s thermal correction directly to carbohydrate oxidation rates (not just fluid loss) and adds an independent altitude correction:

Revised pre-climb timing. Section 04· documents 10-15 min advance intake before >4% climbs. This refinement proposes a stricter criterion — sustained climbs of at least 10 minutes and ≥5% average gradient, anchored exactly 10 minutes prior — currently being evaluated against the active rule.

Outside these priming windows, intake is distributed in regular intervals every 20-30 minutes, sized not to exceed individual gut capacity described in section 02· (60, 90, or 120 g/h based on gut training).

Cf. Jeukendrup (2014) on personalized sports nutrition; Jeukendrup & Wallis (2005) on substrate oxidation; Sawka et al. (2007), ACSM Position Stand on fluid replacement.

Section 01· applies a metabolic phenotype adjustment (Diesel/Balanced/Explosive) to glycogen expenditure. This refinement independently evaluates these multipliers, taking glycolytic predisposition (VLaMax) as an explicit input variable:

The Diesel multiplier differs slightly from the ×0.85 in active use (section 01·) — both figures remain under evaluation.

Cf. Jeukendrup & Wallis (2005) on substrate oxidation by phenotype.

Section 06· limits DIY recipe concentration to ~8% by weight as a practical buffer. However, the gut responds to actual osmolarity in milliosmoles per liter (mOsm/L), which depends on dissolved particle count rather than total powder mass. A large polymer (maltodextrin) yields far fewer particles per gram than a simple sugar (fructose/glucose) of equal weight, requiring weighted calculations:

The maltodextrin coefficient (2.0) reflects long-chain structure — each molecule yields relatively few osmotically active particles. Free monosaccharides (5.5, rather than the 10 suggested by raw molecular weight) avoid overestimating real osmotic impact. Sodium (0.08) accounts for both Na+ cation and counter-anion (chloride).

Independent sodium density alert. A mix may fall within total osmolarity limits yet carry excessive sodium — a bottle exceeding ~850mg Na+ in 550ml (density > ~1500mg Na+/L) triggers an independent alert, as surplus sodium inverts the osmotic gradient regardless of carbohydrate concentration.

Cf. Jeukendrup (2004) on carbohydrate dosing models in sports drinks.

Section 06· recommends anchoring caffeine ~45 minutes prior to the hardest route segment. This refinement formalizes that rule with weight-based dosing and automatic detection of the "critical point": the hardest climb (steepest sustained gradient), or — on flat routes — the start of the final hour on rides over 3 hours.

Cf. Cook & Beaven (2013) on caffeine timing and endurance performance.

Section 02· distinguishes the SGLT1 transporter (saturable at 60 g/h) from the GLUT5 pathway (fructose). This refinement adds two elements: initial intake timing and scaling glucose:fructose ratios with gut training level.

Early hepatic replenishment. The liver, not muscle, experiences the greatest glycogen depletion following overnight fasting — replenishing it early prevents starting in deficit. The first intake is scheduled 20-30 minutes into the ride and includes fructose to engage GLUT5 from the start.

The 120 g/h level is not merely "another table row" — it uniquely requires, in addition to active Gut Training, that the configured mix exceeds the 35% fructose threshold (see full mathematical validation in section 02·). An athlete with active Gut Training using a 2:1 ratio (33.3% fructose) remains capped at 90 g/h.

Cf. Jentjens & Jeukendrup (2005) on glucose:fructose co-transport.

Baseline sweat rate is modeled as a continuous function of dry temperature, with independent correction for high relative humidity:

At 20°C — the midpoint of the linear range on a temperate day — this function returns 0.9 L/h, the baseline against which pre-ride priming climate factors are normalized (see section 21·).

Dynamic intensity factor. Rider pace (solo, drafting, or leading turns) scales sweat rate up or down independently of weather conditions:

Cf. Sawka et al. (2007), ACSM Position Stand on exercise and fluid replacement.

Section 07· details biphasic recovery (Phase 1 immediate liquid / Phase 2 solid) with a 150% rehydration target. This refinement provides a single-window consolidated recommendation as a quick summary:

The protein figure (~0.3 g/kg) is slightly below the ~0.35 g/kg in section 07· — both remain under evaluation within standard literature ranges.

Cf. Ivy & Kuo (1998) on GLUT-4 role in post-exercise resynthesis; Beelen et al. (2010) on nutritional recovery strategies in cycling.

Section 08· isolates draft savings by terrain (flat vs climbing) using a fixed flatland step (×0.70). Because aerodynamic drag scales with the square of speed, draft savings increase with speed. This refinement replaces the fixed step with a continuous function scaling linearly between 15 and 40 km/h, up to 35% savings at 40 km/h.

Cf. Hausswirth et al. (1999) on energy cost of drafting.

Sections 03·/05·/14· apply a flat 75% replenishment rule. That percentage does not distinguish a 45-minute ride from a 6-hour ride: on short rides, losing under 2% body mass does not measurably impair performance. This refinement replaces the flat 75% with an explicit final deficit target for the ride.

Deliberately not a 1:1 replacement — carrying enough liquid to prevent any body mass loss is unnecessary and cumbersome; the goal is staying within established neuromuscular performance thresholds.

Cf. Sawka et al. (2007), ACSM Position Stand on exercise and fluid replacement.

Section 12· calculates an initial caffeine dose (2.0 mg/kg, 45 min before the critical climb) — suitable for moderate rides, but insufficient on long rides where caffeine serum half-life (4-6 hours) leads to significant clearance. This refinement adds maintenance redosing at a reduced fraction of the initial dose.

Each caffeine event may suggest a specific pantry product closest to the target dose without exceeding it — never rounding up, due to individual tolerance and adverse effect thresholds.

Cf. Cook & Beaven (2013) on caffeine timing and endurance performance.

Sodium bicarbonate acts as an extracellular buffer, delaying metabolic acidosis during high-intensity efforts. This refinement provides two distinct protocols tailored to individual GI tolerance — acute loading is simpler but carries real GI distress risks; chronic loading eliminates most risk in exchange for advance preparation.

The "Sensitive Stomach" option uses chronic loading — requiring multi-day planning, but virtually eliminating supplement-induced GI distress.

Cf. Grgic et al. (2021) on sodium bicarbonate supplementation and performance.

Section 07· details biphasic recovery with a single carbohydrate target (~1.2 g/kg). This refinement — featured in Card 05 of the active planner — offers a second alternative profile: less carbohydrate combined with more protein stimulates glycogen synthesis via insulin response while remaining gentler on a fatigued stomach.

Cf. Beelen et al. (2010) on nutritional recovery strategies in cycling.

For morning start times (before 10:00), carbohydrate loading begins the day before rather than at breakfast — arriving at the start line with full hepatic and muscle glycogen stores.

Pre-ride hydration and sodium adjusted for expected climate. Pre-ride fluid and sodium scale with forecast temperature and humidity, using section 14·'s continuous sweat rate function normalized against a temperate reference day:

In warmer or more humid weather, baseline sweat rate exceeds 0.9 L/h and the climate factor scales above 1.0; on cold days, it stays at its minimum.

Cf. Sawka et al. (2007), ACSM Position Stand on fluid replacement; Burke et al. (2011) on carbohydrate loading strategies.

Section 04· covers general pre-climb timing (>4% gradient). On steep ascents (≥8% average gradient), splanchnic blood flow is strongly diverted to active muscle, making intake placement critical — RATIO evaluates three strategies in priority order:

Branch 1 — Prior False Flat. If gradient in the 500m immediately prior drops below 4%, intake is moved forward to that segment — eating just before steep pitches begin.

Branch 2 — Descent Initiation Post-Summit. If no prior false flat exists, the algorithm scans forward for sustained descent — gradient ≤0% maintained for ≥300m — shifting intake past the summit.

Branch 3 — Long Ascent Without Summit in View. If neither branch identifies a natural point within ~20 minutes of climbing, the recommendation shifts to "small liquid sips during the climb" — water-diluted gel or sports drink, far more tolerable on steep pitches than solid food.

Cf. Pfeiffer et al. (2012) on nutritional intake during competition and tactical safety factors.