Study: NCT03804008

Intervention type: DRUG
Group type: ACTIVE_COMPARATOR
Intervention: Ultrasound-guided corticosteroid injection
Description: A 21-gauge, 40 mm needle is connected to a 2.5 cm3 syringe filled with 1 ml Triamcinolonhexacetonid 20mg/ml + 1 ml Lidocain 10 mg7ml. The skin is cleansed with Chlorhexidine alcohol 0.5 %. The needle is inserted with a medial approach under ultrasound-guidance aligned to the long axis of the ultrasound transducer. The injection is placed anterior to the plantar fascia insertion on the calcaneal bone in the region of maximal fascia thickness. Participants are asked to start performing the exercise as soon as they feel ready but not before 24 hours after the injection. Furthermore, they are asked not to progress the method used to achieve 8RM when they start to do the exercise after the injection until Week 3 of the exercise programme. If standing on both feet was sufficient to achieve 8RM at baseline, the participant must not perform the exercise single-legged or to wear a backpack with weights after the injection regardless of any pain reduction afforded by the injection.

Intervention type: OTHER
Group type: ACTIVE_COMPARATOR
Intervention: Heavy-slow resistance training
Description: Participants will be asked to complete a heel raise standing with the forefoot on a step. The toes are maximally dorsi flexed by placing a towel underneath them. The participant is instructed to perform a heel raise to maximal plantar flexion in the ankle joint and afterwards to lower the heel to maximal dorsiflexion. Supporting oneself for balance by placing the hands on a wall or a rail is allowed. Participants are instructed in performing the exercise with a load as heavy as possible but no higher than 8RM and for as many sets as possible every other day.

Intervention type: OTHER
Group type: ACTIVE_COMPARATOR
Intervention: Heavy-slow resistance training
Description: Participants will be asked to complete a heel raise standing with the forefoot on a step. The toes are maximally dorsi flexed by placing a towel underneath them. The participant is instructed to perform a heel raise to maximal plantar flexion in the ankle joint and afterwards to lower the heel to maximal dorsiflexion. Supporting oneself for balance by placing the hands on a wall or a rail is allowed. Participants are instructed in performing the exercise with a load as heavy as possible but no higher than 8RM and for as many sets as possible every other day.

Intervention type: OTHER
Group type: ACTIVE_COMPARATOR
Intervention: Fundamental advice and a silicone heel cup
Description: Participants receive brief information about pathology, risk factors and advice on how to decrease activities that lead to symptom flares and slowly increase their activity level based on their symptoms. They also receive a leaflet that includes the same information as the research assistants will deliver orally after inclusion and a silicone heel cup.

Intervention type: OTHER
Group type: ACTIVE_COMPARATOR
Intervention: Fundamental advice and a silicone heel cup
Description: Participants receive brief information about pathology, risk factors and advice on how to decrease activities that lead to symptom flares and slowly increase their activity level based on their symptoms. They also receive a leaflet that includes the same information as the research assistants will deliver orally after inclusion and a silicone heel cup.

Intervention type: OTHER
Group type: ACTIVE_COMPARATOR
Intervention: Fundamental advice and a silicone heel cup
Description: Participants receive brief information about pathology, risk factors and advice on how to decrease activities that lead to symptom flares and slowly increase their activity level based on their symptoms. They also receive a leaflet that includes the same information as the research assistants will deliver orally after inclusion and a silicone heel cup.