this study will investigate the structure of the Achilles tendon and functional tests in road runners compared to treadmill runners.

Healthy runners (road and treadmill runners) who run regularly at least twice a week for half an hour, over 80% of the training on the treadmill or road, will be recruited for the study.

All subjects will fill out a demographic questionnaire for personal details (age, sex, height, weight, past injuries, training). Each participant will undergo functional tests in random order: 1. Examination of the morphology of the Achilles tendon - will be examined by ultrasound tissue characterized (UTC) 2. Balance test - Y Balance Test 3. Proprioception test - AMEDA device 4. Muscle strength test - manual dynamometer for testing gastrocnemius muscle strength. 5. Gastrocnemius muscle endurance test - single leg heel raise test until fatigue.

A comparison will be made between the two study groups.

Inclusion Criteria:

• run regularly at least twice a week for half an hour,
• over 80% of the training on a treadmill or road

Exclusion Criteria:

• pain or injury to Achilles tendon during the 6 months, preventing running for at least 3 days.
• past Achilles tendon surgeries,
• sprained ankle in the last six months,
• lower limb and back pain while running
• participants who report running with minimalist shoes.

healthy runners who run on a regular basis, without injuries or pain during the last 6 months