This study investigates the acute effect of isotonic versus isometric exercise versus walking on pain in individuals with plantar heel pain and an ultrasound-diagnosed plantar fasciopathy. The hypothesis is that isometric exercise will induce greater participant rated pain relief than isotonic exercise and walking during aggravating activity.

Participants will be required to attend three sessions (isometric, isotonic, or walking) within a maximum of two weeks. The order in which the participant completes the sessions will be randomised.There will be a minimum of 48 hours between sessions. To account for potential time of day differences in terms of pain, all sessions will be performed within ±1 hour (e.g. if the first session is performed at 10 AM the remaining two sessions will be performed between 9 and 11 AM). After diagnosis, randomisation of the order of which the sessions will be performed, and have their pain during an aggravating activity examined (aggravating activities will be static stance, half squat or heel raise). Subsequently the participants will be instructed in performing either isotonic or isometric heel raise or walking, (determined according to the randomisation) by a physiotherapist.

All statistical analyses will be performed according to a pre-established analysis plan using STATA ver. 14. The assumption of negligible carryover effects is investigated with a preliminary test. The primary analysis will test the presence of a difference in EIH between isotonic and isometric exercise and walking and a 3 X 2 repeated measures ANOVA will be performed. Independent factors will be exercise type (isometric vs. isotonic vs. walking) and time (pre vs. post). If an interaction is found, post-hoc paired t-tests will be performed. The standardised mean difference (effect size) and its confidence intervals will be calculated and presented in a forest plot. Apriori it has been determined that no conclusions will be made favouring either of the exercises nor walking if pain is reduced less than the clinically important difference of 19 mm VAS. In addition, the proportion of clinically relevant pain reductions (i.e. a pain reduction of at least 19 mm VAS) will be calculated. EIH by pain experienced during the aggravating activity before the exercises and walking will also be presented in a plot.

Secondary analyses using a 3 X 2 repeated measures ANOVAs will test if there is a difference in the thickness of the plantar fascia and a difference in PPTs from before to after either of the exercises or walking and a difference in pain experienced during the exercises or walking. If interactions are found post-hoc paired t-tests will be performed. A paired t-test will be performed to investigate potential differences in plantar fascia thickness from before to after the initial PPT and pain aggravating activity are performed. Effect sizes will be calculated for the difference in pressure pain threshold and plantar fascia thickness. The association between thickness of the plantar fascia and the difference in pain from before to after the exercise activities will be investigated using Pearson's correlation coefficient.

Inclusion Criteria:

• History of inferior heel pain for at least three months before enrolment
• Pain on palpation of the medial calcaneal tubercle or the proximal plantar fascia
• Thickness of the plantar fascia of 4.0 mm or greater
• Pain during at least one of three pain aggravating activities (static stance, half squat and heel raise)
• Mean heel pain of ≥ 20 mm on a 100 mm VAS [0mm = no pain, 100mm = worst pain imaginable] during the past week

Exclusion Criteria:

• Below 18 years of age
• History of inflammatory systemic diseases
• Pain or stiffness in the 1st metatarsophalangeal joint to an extent where the exercises cannot be performed
• Prior heel surgery
• Pregnancy
• Pain medication
• Corticosteroid injection for plantar fasciopathy within the past six months