Question 1

How accurate is the Riegel formula for predicting race times?

Accepted Answer

The Riegel formula (T₂ = T₁ × (D₂/D₁)^1.06) is reasonably accurate for most runners, with predictions typically within 2-5% of actual race times when conditions are optimal. Accuracy depends on several factors Distance ratio: Most accurate when predicting between similar distances (e.g., 5K to 10K, or half marathon to marathon). Less accurate for large jumps (e.g., 5K to marathon) Training specificity: Works best if you've trained for the target distance. A 5K specialist will likely underperform marathon predictions Current fitness: Assumes consistent training and fitness level between the known race and predicted race Course conditions: Predictions assume similar terrain, weather, and course difficulty The 1.06 exponent represents the average fatigue factor—as distance increases, pace must decrease. However, individual fatigue resistance varies: endurance-focused runners may outperform predictions on long distances, while speed-focused runners may excel at shorter races. Example If you run a 5K in 25:00 (5:00/km pace), the Riegel formula predicts a 10K time of ~52:17 (5:14/km pace). For well-trained runners with 5K-specific fitness, this is typically accurate within ±2 minutes.

Question 2

What is the difference between easy pace, tempo pace, and interval pace?

Accepted Answer

These training paces target different physiological adaptations based on Jack Daniels' Running Formula, the gold standard for evidence-based training zones. Training Pace Breakdown Pace Type % of Race Pace Purpose Duration Easy 65-78% slower Aerobic base, recovery, fat oxidation 20-90+ min Marathon 80-90% of 5K pace Lactate threshold, race-specific 60-120+ min Threshold/Tempo 88-92% of 5K pace Raise lactate threshold, improve endurance 20-40 min Interval 95-100% of 5K pace VO₂max improvement, aerobic power 3-5 min reps Repetition Faster than 5K pace Speed, running economy, anaerobic capacity 200-800m reps Example weekly structure (40 mpw) Monday: 6 miles easy (builds aerobic base without stress) Tuesday: 8 miles with 20 min tempo (lactate threshold work) Wednesday: 5 miles easy recovery Thursday: 5×1000m intervals at interval pace with 400m recovery (VO₂max) Friday: Rest or 4 miles easy Saturday: 12 miles long run, mostly easy pace Sunday: Rest or cross-training The 80/20 rule Research shows that 80% of your weekly mileage should be at easy pace, with only 20% at moderate-to-hard intensities for optimal adaptation and injury prevention.

Question 3

How should I adjust my pace for hills, heat, or trail running?

Accepted Answer

Environmental and terrain factors significantly affect running pace—often by 10-30% or more. Smart runners adjust by effort (heart rate or perceived exertion) rather than maintaining flat-road paces. Pace Adjustments by Condition Condition Pace Impact Adjustment Strategy Hills (uphill) +10-30 sec/km per 1% grade Run by effort, accept slower pace, power hike steep sections (>15%) Hills (downhill) -5-15 sec/km, but higher impact Control effort, avoid pounding quads, use turnover not stride Heat (25-30°C) +10-20 sec/km Slow down 10-15%, increase hydration, run early/late Humidity (>70%) +5-15 sec/km Expect higher heart rate, adjust by RPE, wet clothing for cooling Wind (headwind) +10-30 sec/km Run by effort, use drafting in groups, adjust expectations Trails (technical) +30-60 sec/km or more Focus on effort and safety, accept slower paces, use time-based goals Altitude (>2000m) +10-20 sec/km Slow down 10-15%, allow acclimatization time, monitor heart rate The "Effort-Based Approach" For variable terrain or weather, use heart rate zones or RPE (rate of perceived exertion) instead of pace targets. A Zone 2 easy run should feel conversational regardless of pace—accept 6:30/km on flat roads but 7:30/km on hills. Example adjustment If your easy pace is 5:30/km on flat roads, expect 6:00-6:30/km on rolling hills, 6:30-7:00/km in heat/humidity, and 7:00-8:00/km on technical trails. All at the same cardiovascular effort.

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