Why One Runner Gets Injured at 15 Miles Per Week While Another Can Run 40
One of the most common misconceptions among runners is that injuries occur because of high mileage.
The logic seems straightforward:
More miles = more stress = greater injury risk.
However, if total mileage were the primary driver of injury, elite runners logging 70 to 100 miles per week would be injured constantly.
Instead, research and clinical experience suggest a different explanation.
The risk of injury is often influenced less by the amount of work being performed and more by how rapidly that workload changes.
This concept is commonly referred to as the Acute:Chronic Workload Ratio (ACWR), a framework used throughout sports performance and sports medicine to better understand injury risk.
What Is the Acute:Chronic Workload Ratio?
The Acute:Chronic Workload Ratio compares an athlete's recent training load to the amount of work they have been consistently performing over time.
In simple terms:
Acute workload = what you've done recently (typically the last 7 days)
Chronic workload = what you've consistently done over the previous 3-6 weeks
The purpose of the ratio is to determine whether your body is being exposed to a level of stress it is prepared to tolerate.
Rather than focusing on the absolute amount of training, the model focuses on the relationship between current training and historical training.
Why Relative Workload Matters More Than Absolute Workload
Consider two runners:
Runner A
Average weekly mileage: 30 miles
Current week mileage: 35 miles
Runner B
Average weekly mileage: 5 miles
Current week mileage: 15 miles
At first glance, Runner A appears to be under greater stress because they are running more total miles.
However, Runner B has tripled their workload in a single week.
From a tissue adaptation standpoint, this represents a substantially larger challenge.
The body does not simply respond to workload.
It responds to changes in workload.
Muscles, tendons, bones, cartilage, and connective tissue all adapt gradually. When training increases faster than those tissues can adapt, injury risk rises.
Why Running Injuries Often Occur During Training Progress
Many runners are surprised when injuries occur during periods of motivation and consistency.
A typical scenario looks like this:
Training has been inconsistent for several months
A race registration creates renewed motivation
Weekly mileage increases rapidly
Symptoms begin appearing within several weeks
The injury is often attributed to a specific run, workout, or movement.
In reality, the issue may have started weeks earlier when training load increased beyond the body's current capacity.
The symptomatic run is frequently the final stressor rather than the root cause.
Common Examples of Workload Spikes
Workload spikes are not limited to running mileage.
They occur whenever physical demand increases faster than the body can adapt.
Examples include:
Beginning marathon training after a prolonged break
Returning to running after injury
Increasing long-run distance too quickly
Adding speed work without adjusting recovery
Participating in multiple races within a short period
Increasing strength training volume while maintaining the same running volume
In each case, the challenge is not necessarily the activity itself but the rate of progression.
What the Research Suggests
One of the most consistent findings in sports medicine literature is that athletes who maintain a higher chronic workload often demonstrate greater resilience to injury than athletes who experience repeated workload spikes.
This finding is important because it shifts the focus away from avoiding activity and toward developing capacity.
A runner with a well-developed training base is frequently better protected against injury than a runner who repeatedly alternates between inactivity and aggressive training increases.
In other words, fitness itself can be protective.
Practical Applications for Runners
Understanding workload management does not require complex calculations.
Most runners can benefit from asking three simple questions:
1. What has my average training looked like over the last month?
Recent consistency is often more important than peak performance.
2. Am I increasing multiple variables at the same time?
Mileage, intensity, hills, speed work, and strength training all contribute to total workload.
3. Is my body demonstrating it can tolerate the current workload before I add more?
Progression should be earned through adaptation rather than forced through motivation.
The Bottom Line
The question most runners ask is:
"How much running is too much?"
A more useful question is:
"How much running is too much relative to what my body has recently been prepared for?"
In many cases, injuries are not caused by excessive training volume.
They are caused by excessive increases in training volume.
The runners who stay healthy long term are rarely the runners who avoid stress.
They are the runners who build capacity gradually, consistently, and intentionally.
At Resilience Chiropractic + Performance, we help runners identify the factors contributing to recurring injuries and create training strategies that support long-term performance rather than short-term setbacks.
If you're dealing with recurring knee pain, Achilles pain, shin splints, or running injuries, schedule a free discovery call to learn how workload management and performance-based rehabilitation can help keep you running.
