Expert panel characteristics

Thirty-eight experts from seven different countries were invited to participate (Table 1). Two (5%) academic experts did not meet selection criteria due to having published less than five journal articles on PHP or muscle strengthening exercises. Of the remaining 36 experts, 24 (67%) agreed to participate.

Table 1 Expert panel characteristics (n = 24) Round 1

All 24 participants who agreed to participate completed the open-ended questionnaire.

Exercise prescription

Twenty-two out of 24 (92%) respondents stated they would prescribe a progressive foot strengthening program for PHP. Of the two respondents who indicated they would not prescribe such a program, they agreed they would use a reloading strategy in the right circumstances:

‘…reloading with graded loading programme in standing (so arguably with a strength component in the exercise due to the functional nature of the exercise)…’.

and.

‘…I often prescribe whole body, or lower limb exercise or CV [cardio-vascular] exercise if the patient is coping with the core intervention components…’.

Strength training goals

Seven themes were extracted regarding the goals of strength training exercises for PHP including: addressing muscle weakness (n = 7), increasing tissue load/capacity (n = 6), reducing strain to the plantar fascia (n = 4), improving impact absorption of the foot (n = 3), improving function (n = 2), reducing arch deformation (n = 2), and reducing pronation (n = 1).

Indications and contraindications

The two most common responses regarding indications for a progressive strengthening program were that it can be applied to all patients (n = 6) and to athletic or physically active individuals (n = 4) (Additional file 2).

Only three contraindications for a progressive strengthening program were raised. Contraindications included the presence of a neurological (n = 1), bone (n = 1) or fat pad (n = 1) pathology (Additional file 2).

Exercise selection

The most common exercises were heel raise variations (n = 10), digital plantarflexion (n = 8), and the short foot exercise (n = 8) (Additional file 3).

Muscles to be targeted

The most common muscles to be targeted were foot intrinsics as a group (n = 6) (Additional file 4). Specific muscles mentioned included: calf (n = 2), flexor hallucis longus (n = 2), flexor digitorum brevis (n = 1), flexor digitorum longus (n = 1), tibialis posterior (n = 1), and adductors (n = 1) (Additional file 4). The term ‘adductors’ was mentioned but not defined as hip or foot adductors.

Movement concepts

Three themes emerged as movement concepts rather than specific exercises to be prescribed, including applying a talar neutral position (n = 3), foot core (n = 1), and toe posture (n = 1).

Dosage variables

The recommendations of variables to be used when prescribing a progressive strengthening program were sets and repetitions, time under tension, or using a repetition maximum. The most common dosage variable used was sets and repetitions (n = 14), followed by achieving a repetition maximum (n = 3), and time under tension (n = 2).

The most common number of sets was three (n = 5), four (n = 3), and then five (n = 3). The most common number of repetitions was 10, 12 and 15 (n = 5), however there was a range of repetitions offered (from 1 to 25). Occasionally, the repetition or set range was dependent on the exercise choice.

Progression of exercise

The most common responses for progressing difficulty of exercise were to increase volume (n = 8), weight (n = 5), and complexity (n = 3).

Round 2

A three-stage progressive strengthening program was derived from the results of Round 1 for each vignette. Eighteen of the 24 (75%) experts completed Round 2 of the study, although one completed only the first vignette. Results for Round 2 are detailed below and in Table 2.

Table 2 Progressive strengthening programs with exercises, exercise variables and their levels of agreement from Round 2 Younger athletic adult

Seven of 9 (78%) exercises achieved consensus. The exercises that did not achieve consensus were heel raise seated with digits dorsiflexed (67%) and short foot exercise while standing (67%). Twenty-six of 27 (96%) exercise training variables met consensus. The heel raise seated with digits dorsiflexed did not reach consensus for frequency of exercise (daily).

Overweight middle-aged adult

Five of 8 (63%) exercises achieved consensus. The exercises that did not achieve consensus were towel scrunch with inversion and eversion (59%), single leg standing on an unbalanced surface (53%), and short foot exercise seated (59%). Twenty-two of 24 (92%) exercise training variables reached consensus.

Older adult

Five of 8 (63%) exercises achieved consensus. The exercises that did not achieve consensus were towel scrunches (53%), towel scrunch with inversion and eversion (41%), and short foot exercise while seated (65%). All 24 (100%) exercise training variables reached consensus.

Progressions

The progressions of exercises and stages of the program had 54% agreement, so did not reach consensus in Round 2. The progressions were based on increasing repetitions (volume) first. This was outlined as: ‘Each week the program progresses by adding two repetitions and keeping the weight and other variables the same. All participants begin on Stage 1 of the exercise regime. If there is no perceived difficulty or pain, then progression to Stage 2 and so on for Stage 3.’

Round 3

All 18 (100%) experts completed Round 3 of the study. The exercises that did not reach consensus in Round 2 were replaced in Round 3 with the exercises that were suggested most frequently by the experts in Round 2. For example, the towel scrunch with inversion and eversion did not meet consensus in Round 2 for the older adult (41%), so it was replaced with short foot exercise seated, which was the most frequently suggested replacement exercise. Following these replacements, all three progressive strengthening programs met consensus in Round 3 (Table 3).

Table 3 Selected exercises, stage of progression, and agreement from Round 3 (n = 18) Progressions

Exercise progressions were updated to increase weight and then functionality, rather than increase volume (repetitions) first. This change was made in response to feedback from the experts in Round 1. This progression strategy achieved 100% consensus. The final progressive strengthening programs are presented in Table 4.

Table 4 Strengthening programs that reached consensus after Round 3