The load borne by the Achilles tendon during exercise: a systematic review of normative values

Key points

1. 01AT load during walking ranges from approximately 2 to 3 times body weight (BW)
2. 02AT load during running ranges from approximately 4 to 7 BW
3. 03Strengthening exercises produce AT loads from approximately 0 to 7 BW depending on the specific exercise
4. 04Only 3 of 11 studies directly assessed AT load during strengthening exercises commonly used in rehabilitation
5. 05Methodological variability, especially in calculating the Achilles tendon moment arm, limits direct comparison of values across studies

How it was conducted

Design

Systematic review (PRISMA-based)

Databases

PubMed, Embase, Cochrane; searched up to May 21, 2021

Inclusion criteria

Studies reporting AT load in newtons relative to body weight in humans during activities or exercises

Studies included

11 studies

Participants

Healthy adults; number per study ranged up to 30, with a median around 10-15; mean age approximately 30 years

Measurement methods

Inverse dynamics (8 studies), inverse-dynamics-based static optimisation (3 studies), shear wave tensiometry (1 study), quadratic force-length function (1 study)

What they found

• AT load during walking ranged from approximately 2 to 3 BW across studies; Keuler et al. and Gheidi et al. showed a gradual increase from 3.x to higher BW values with increasing speed
• AT load during running ranged from approximately 4 to 7 BW; both parameters tended to increase together but the relationship was not strictly linear
• Three studies tested AT load during strengthening exercises; the load ranged from approximately 0 to 7 BW depending on the exercise performed
• Heel raises performed with loads ranging from 100% to 150% body weight were included among the strengthening exercises tested (Yeh et al.)
• Kharazi et al. calculated an AT force of only 2.x BW at a given walking speed, approximately 27% lower than Gheidi et al. (3.71 BW) at the same speed, illustrating inter-study measurement discrepancies
• Different methods of estimating the AT moment arm can lead to variations in calculated AT load of up to 4 BW (Krikelis et al.)
• Running on a treadmill generated more tendon force than running over ground; men displayed significantly greater AT load than women in one comparative study

Limitations

• High heterogeneity in activities performed, participant characteristics, and measurement methods made quantitative data pooling unreliable
• No non-invasive gold standard exists for AT load assessment, making it difficult to judge the accuracy of different methods
• All data were obtained in healthy participants, so applicability to pathological tendons (tendinopathy, post-rupture) is unknown
• The review was not registered in PROSPERO and formal evidence-level assessment was not conducted

Why it matters

For patients

People recovering from Achilles tendinopathy can use this data to understand that common exercises like heel raises place very different demands on the tendon than walking or running, supporting a gradual return-to-activity approach.

For clinicians

Clinicians can use the load hierarchy (walking less than low-demand exercises less than higher-demand exercises less than running) to design progressive rehabilitation protocols, while remaining cautious about exact numbers given methodological variability.

For readers

This review provides the first synthesis of normative Achilles tendon load values expressed relative to body weight across exercise types, offering a practical framework for progressive tendon loading, though further research is needed to fill gaps in injured populations.