The Base Phase establishes the foundational adaptations required for effective performance later in the season. Its primary objective is to enhance aerobic capacity, tissue durability, and metabolic efficiency through consistent, sub-threshold running.
Increased mitochondrial density and enzymatic activity, improving aerobic ATP production
Enhanced integrity of soft tissues (muscle, tendon, ligament) through gradual collagen remodeling
Improved metabolic flexibility, enabling more efficient utilization of both lipids and carbohydrates
Neuromuscular adaptation to frequency, reinforcing movement patterns and reducing mechanical cost
Positive changes in anthropometry, including improved body composition over time
Before progressing to intensity-based decisions, athletes must determine two variables: weekly frequency and total weekly volume.
While mileage is an important determinant of endurance performance, current research identifies it as the third strongest predictor. The first two are:
Number of training sessions per week
Accumulated years of consistent running
Total weekly volume (mileage)
Since training age cannot be increased retroactively, manipulating frequency becomes the most effective lever for long-term progression. Increasing frequency produces several important outcomes:
Distributes mechanical load across more sessions, reducing peak stress and lowering injury risk
Provides more frequent metabolic stimulus, enhancing aerobic enzyme activity and mitochondrial signaling
Facilitates gradual volume expansion, as each run requires only modest increases to raise weekly totals
Improves tissue recovery, as frequent blood flow and repeated low-level strain promote collagen realignment and repair
During Base training, volume should increase progressively until it reaches approximately 80% of the athlete’s planned peak seasonal mileage. From there:
Mileage may increase slightly during the Support Phase (especially for longer-distance athletes)
Volume typically plateaus or modestly decreases during the Specific Phase, where intensity and race-specific work become the priority
Athletes should identify a realistic and repeatable four-week peak. A conservative approach is recommended:
Do not base peak volume on a single “high week” from a previous season
Instead, use the highest four-week average as the reference point
Aim to exceed that monthly average slightly—not dramatically
Example:
If you reached 96 km for one or two isolated weeks last season, but your highest four-week rolling average was 72 km, the goal should not be a 112 km peak week. A more appropriate target would be 80–88 km consistently over four weeks.
This approach optimizes adaptation while minimizing injury risk.