Two weeks covering the same kilometres can impose very different loads. In one, you run gently on familiar terrain; in the other, you introduce intervals, hills and a race after poor sleep. The total matches, but your body’s experience changes.
For a recreational athlete, managing load starts with recognising that difference. You do not need to predict an injury; you need to notice changes your history has not yet shown you can tolerate. Recording what you do and how you respond helps you choose the next session, without promising to avoid every injury.
External and internal load: work and response
External load describes the work performed: distance, duration, repetitions, weight, elevation gain, accelerations, sprints and physical contacts. Surface and competition density also deserve a note: how many races or matches are clustered together and how much time separates them. No single variable captures every demand.
Internal load describes your response: perceived exertion, heart rate and subjective fatigue. Perceived exertion expresses how demanding the session felt to you.
Your response can also change between days. Sleep, stress, heat, illness, recovery and previous experience alter the response to similar external loads. The International Olympic Committee consensus on load and injury includes sporting and non-sporting demands in this framework.
Your current capacity is not someone else’s
Adaptation does not progress at the same rate across all systems and tissues. Feeling able to sustain a pace does not show that muscles, tendons and bones tolerate every combination of impacts and repetitions. There is no universal adaptation timetable for each tissue either.
Your most useful reference is your recent history of work completed with a favourable response. After a break, reconsider that reference rather than automatically returning to your last training level.
Tolerating an isolated session does not show you can tolerate repeating it with less recovery. Look at the sequence: what you did beforehand, how you felt going in and what happened afterwards.
When several new demands accumulate
A load increase is not just extra kilometres. Increasing volume and intensity while introducing hills, a different surface, new shoes or gym work adds several new demands together. Competition can introduce effort, contacts or accelerations that your weekly total does not capture.
This does not mean a new surface or pair of shoes is inherently dangerous. It means you have changed the stimulus and need to observe your response.
A load change should not be presented as the sole cause of injury. Previous injuries, health, capacity, environment and sporting circumstances all matter; an injury may also involve trauma.
What the evidence actually says
Sports injury is multifactorial. The systematic review by Eckard and colleagues finds relationships between load and injury, with results depending on the measure and timeframe studied. A population association neither calculates your personal probability nor proves which change caused a particular injury.
The 10% rule, limiting weekly increases to that proportion, can serve as a heuristic: a simple planning guide. It has not been established as a universal law of injury prevention. Systematic reviews by Damsted and colleagues in 2018 and Fredette and colleagues in 2022 show limited or heterogeneous evidence in runners. Replacing 10% with another arbitrary percentage does not solve the problem.
The acute:chronic workload ratio, or ACWR, divides a recent load measure by a reference load from a longer period. It describes a relationship between records; it does not directly measure your tissues’ capacity. The conceptual critique of ACWR and methodological critique of load research explain important limitations:
- Time windows are choices that may be arbitrary.
- Mathematical coupling occurs when recent load also contributes to the denominator.
- Choosing distance, duration or exertion changes what the ratio represents.
- Reverse causality can occur: emerging symptoms make you reduce training before an injury is recorded.
- Finding associations does not validate individual prediction.
We therefore do not use “safe” zones, thresholds or predictive calculators.
Load map: five useful questions
The Load map is a brief manual record, not a clinical tool:
- Work completed. Record duration or volume and the relevant variables for your sport. Distinguish planned work from completed work.
- Intensity. Describe perceived exertion for the session and particularly demanding sections.
- Novelty. Note what changed from familiar sessions: pace, surface, equipment, exercise or distribution of work.
- Context. Record sleep, stress, heat, illness and non-sporting load, such as physical work, travel or family care.
- Response. Note how you felt during the session, afterwards and the next day: fatigue, discomfort and ability to move normally.
Optionally, session-RPE combines duration in minutes with the rating of perceived exertion for the whole session: minutes × RPE. On a scale from 0 to 10, 40 minutes at RPE 4 gives 160 arbitrary units. This is a calculation example, not a target or limit.
Use it only as a personal approximation for observing trends. It is not a medical measurement and does not represent the specific load on a tendon or bone. Do not blindly compare people or sports. The systematic review by Jones and colleagues on load and fatigue markers highlights the importance of individual characteristics.
The same distance does not always mean the same load
You could cover the same distance in every example below; what you need to record changes:
| Session or context | What changes | What to observe |
|---|---|---|
| Easy run on familiar terrain | Familiar stimulus and usually manageable effort | Whether your response resembles your history |
| Interval session | Intensity, accelerations and distribution of effort | Overall exertion and response after faster sections |
| Hilly route | Elevation and demands of climbing and descending | How unfamiliar the route is and your subsequent response |
| New surface or shoes | Foot contact conditions and familiarity with equipment | What was new and how you felt |
| Week with poor sleep or high stress | Recovery context and internal response | Whether usual work feels unusually demanding |
The table assigns no risk percentages and does not rank sessions from “safe” to “dangerous”.
Progress through decisions you can revisit
Identify which variable changed. If you want to introduce hills, recognise that descents also form part of the new demand. Change one main variable at a time when possible and keep the others close to familiar conditions.
Consolidate your response before adding more new demands. Review comparable sessions and their subsequent effects, without imposing a universal number of repetitions. Adjust the plan to your individual response: maintaining, simplifying or reducing the load may make more sense than continuing to increase it.
For example, if a new route leaves you with an unusual response, avoid adding both intervals and demanding gym work in the next session. Reconsider the stimulus and seek advice if the response persists. Stopping or seeking professional assessment when concerning signs appear is also part of managing the plan.
A traffic light for action, without diagnosis
- Green: expected fatigue that develops favourably and allows normal function to return. Keep observing; this is not a certificate to increase load.
- Amber: an unusual, persistent or progressively worsening response. Reconsider the next load and seek advice if it fails to improve or limits daily activities.
- Red: intense or sharp pain, deformity, substantial swelling, loss of function, neurological symptoms such as weakness or numbness, inability to bear weight, or systemic symptoms such as fever or significant general illness. Stop the activity and seek professional assessment; obtain urgent care according to severity.
This traffic light guides decisions without identifying diseases. You can develop your observations with our guide to pain after training.
Common mistakes
- Counting only kilometres and overlooking intensity, contacts or elevation.
- Adding volume, intensity and novelty simultaneously.
- Making up missed sessions by packing them into a few days.
- Returning abruptly after a break or copying another athlete’s progression.
- Treating your watch’s score as a medical verdict.
- Ignoring stress and everyday non-sporting load.
- Continuing with progressively worsening symptoms because the plan says it is training time.
YouVisible challenge: your next four sessions
Keep a manual record in a notebook or your notes. YouVisible documents notes and feelings associated with activities; this challenge does not assume a dedicated form or an automatic load calculation.
For each of your next four sessions, record planned and completed work, identify what was new, note perceived exertion and write down your response the next day. Then choose one adjustment for the following session and explain why: keeping the route, removing a new element or reconsidering intensity.
Afterwards, look for differences between similar sessions. The aim is to build an interpretable history for better decisions, not to achieve a perfect score or predict an injury.
Sources
- Consensus: Soligard et al. (2016), How much is too much? IOC consensus statement on load in sport and risk of injury.
- Conceptual critique: Impellizzeri et al. (2020), Acute:Chronic Workload Ratio: Conceptual Issues and Fundamental Pitfalls.
- Methodological critique: Impellizzeri et al. (2020), Training Load and Its Role in Injury Prevention, Part 2.
- Systematic review: Eckard et al. (2018), The Relationship Between Training Load and Injury in Athletes.
- Systematic review: Damsted et al. (2018), Is There Evidence for an Association Between Changes in Training Load and Running-Related Injuries?.
- Systematic review: Jones et al. (2017), Training Load and Fatigue Marker Associations with Injury and Illness.
- Systematic review: Fredette et al. (2022), The Association Between Running Injuries and Training Parameters.
Health note: This content is educational and does not replace assessment by healthcare professionals or an individual plan. No record or metric can diagnose an injury or guarantee its prevention.