Run clever, no difference in risk of injury when comparing progression in running volume and running intensity in recreational runners: a randomized controlled trial

Key points

1. 0116% of intensity-group runners and 19% of volume-group runners sustained a running-related injury during the 16-week focused training period, with no statistically significant difference between groups.
2. 02The original hypothesis that intensity-focused progression would cause 15% more injuries than volume-focused progression was not supported.
3. 03Both small absolute increases in hard-intensity running (0.8 km over 16 weeks) and total volume (6 km over 16 weeks) led to meaningful injury proportions.
4. 04A high dropout rate during the 8-week preconditioning period (about 47%) reduced statistical power and may have introduced confounding.
5. 05Real-time GPS-based individualised feedback was used to monitor and guide running intensity and volume compliance throughout the trial.

How it was conducted

Design

Randomised parallel-group trial with 24-week follow-up (8-week preconditioning + 16-week specific focus training period)

Participants

839 healthy recreational runners (18-65 years, 1-3 sessions/week for prior 6 months) randomised at baseline; 447 entered the intervention period

Groups

Schedule Intensity (Sch-I, n=221): progressive increase in weekly volume of running at hard intensity (>=88% VO2max); Schedule Volume (Sch-V, n=226): progressive increase in total weekly running volume at easy intensity (<=80% VO2max)

Primary outcome

Running-related injury (RRI) defined as time-loss injury lasting at least 7 days

Analysis

Instrumental variable (IV) approach as primary analysis; intention-to-treat and per-protocol as secondary; cumulative injury risk difference reported at weeks 2, 4, 8, and 16

What they found

• During the 16-week intervention, 80 runners sustained an RRI: 36/221 (16%) in Sch-I and 44/226 (19%) in Sch-V.
• Cumulative incidence proportion in Sch-V (reference): 4.6% at week 2, 8.2% at week 4, 13.2% at week 8, 28.0% at week 16.
• Risk differences (Sch-I minus Sch-V): RD at week 2 = 2.9% (95% CI -5.7% to 11.6%, p=0.51); week 4 = 1.8% (95% CI -9.1% to 12.8%, p=0.74); week 8 = -4.7% (95% CI -17.5% to 8.1%, p=0.47); week 16 = -14.0% (95% CI -36.9% to 8.9%, p=0.23).
• No statistically significant risk difference was found at any time point across week, day, kilometre, or minute time scales.
• Mean compliance during the specific focus training period was 75% (+-23) in Sch-I and 76% (+-22) in Sch-V.

Limitations

• High dropout during preconditioning (~47% in each group) substantially reduced statistical power and may have introduced imbalance in unmeasured covariates.
• VO2max was estimated from a self-administered field running test rather than direct laboratory measurement, potentially reducing precision of intensity prescription.
• Randomisation occurred prior to preconditioning rather than immediately before the intervention period, increasing risk of confounding from dropout-related imbalance.
• The relative progression structure may have favoured the intensity group by allowing more recovery time between sessions, limiting generalisability to absolute-progression schedules.

Why it matters

For patients

Recreational runners can be reassured that gradually increasing hard-intensity running does not appear to be more dangerous than gradually increasing overall mileage, but both approaches still carry a meaningful risk of injury.

For clinicians

Neither a volume-focused nor an intensity-focused progression strategy was significantly safer, so clinical decisions should weigh individual runner characteristics and consider that even modest load increases produce injury rates above 15-28% over 16 weeks.

For readers

This trial highlights that the interaction between training variables is complex, and future injury prevention research should account for all modifiable variables rather than isolating single ones.