Pelvic floor strength will be measured by the research associate women's health physiotherapist at week 6, 12 and 24. Pelvic floor strength will be measured digitally using the modified oxford scale ranging from 0-5, 0 being no discernible contraction and 5 overcoming strong resistance. Over-activity and co-ordination of the pelvic floor muscle will be assessed by a simple yes/no answer following digital vaginal examination.

Musculoskeletal physiotherapy measures will be assessed by the research associate women's health physiotherapist at weeks 6, 12 and 24. Posture, movement patterns, breathing will be objectively evaluated and commented on. The abdominal muscles (rectus diastasis) will be assessed by measuring the distance between the internal borders of the rectus abdominus muscle by placing the fingers vertically on the linea alba 4 cm above and below the umbilicus, during a curl up movement. Scoring is obtained through an approximation of centimetre width separation and the tone of the linea alba structure. The larger the score in centimetres the greater the separation of the rectus abdominus muscle.

The Pelvic Floor Distress Inventory will be completed at 6, 12 and 24 weeks by all participants. The Pelvic Floor Distress Inventory is scored ranging from 0-300, 0 being the least distress and 300 being the greatest distress.

The International Consultation on Incontinence Questionnaire - Vaginal Symptoms will be completed at 6, 12 and 24 weeks by all participants. The International consultation on Incontinence Questionnaire - Vaginal Symptoms evaluates vaginal symptoms, associated sexual matters and impact on quality of life. Three scores are generated. Subscales range from 0-53 vaginal symptoms, 0-58 sexual matters and 0-10 overall impact on quality of life. 0 represents the least bothersome in each subscale. The subscales are not incorporated in an overall score.

The World Health Organisation Quality of Life Questionnaire (WHOQOL-BREF) will be given to participants in paper. The WHOQOL-BREF provides an overall quality of life/wellbeing score and allows calculation of a score for each of the four sub-scales (physical health, psychological, social relationships and environment). The four domain scores are scaled in a positive direction (higher score equal higher quality of life). The mean score of items within each domain is used to calculate the domain score.

The Edinburgh Post Natal Depression Scale (EPDS) asks participants to answer questions by reflecting on the past 7 days. The questionnaire produces a total score of postnatal depression symptoms (range 0-30) with a score of 13 and above indicating likelihood of a depressive illness of varying severity

Body composition (fat mass, fat-free mass and bone mineral density) will be measured at weeks 6 and 24 by a whole-body dual-energy x-ray absorptiometry (DXA) scan.

Bone microarchitecture will be determined at weeks 6 and 24 by a HRpQCT scan; two scans of the tibia (distal 4% and 30% site) will be performed on the non-dominant leg to assess training-induced changes in bone microarchitecture and density.

Tendon stiffness and young's modulus will be measured using ultrasonography with a linear array probe. Patella tendon length and elongation will be calculated as the distance from the apex of the patellar and the shadow created by a fixed marker. Patella tendon stiffness will be calculated by dividing knee extensor torque by the estimated patella tendon moment arm. Knee extensor torque will be calculated as the sum of the measured knee extension torque and the antagonistic torque, estimated through the root mean square of the biceps femoris muscle electromyography signal. Force-elongation data will be fitted with to a second order polynomial curve to determine patella tendon stiffness. Tendon CSA will be assessed along the full resting length of the tendon on the axial plane through ultrasonography. Young's modulus will then be calculated as tendon stiffness multiplied by the ratio of tendon length over tendon cross-sectional area.

Fascicle length of the vastus lateralis will be assessed at weeks 6, 12 and 24 by the acquisition and analysis of images taken using B-mode ultrasonography (MyLab Omega, Esaote, UK), with a linear array probe. Images will be obtained with the participant lying at rest in a supine position. Images will be taken at 50% of the length of the vastus lateralis and at the midsagittal line of the muscle. The transducer will be aligned to the fascicle plane to allow optimal capture of the fascicles.

Muscle protein/collagen turnover will be measured from blood, saliva and skeletal muscle biopsy samples. Participants will provide a saliva sample before being given a drink of 'heavy' water (D2O); water that is enriched with a metabolic isotope tracer that can be used to evaluate the rate of protein and collagen turnover by determining the rate of tracer incorporation into muscle tissue. The muscle biopsy will be used to measure the incorporation of deuterated alanine into muscle tissue over time and enable the calculation of the fractional rate of muscle protein synthesis by mass spectrometry.

We intend to estimate whole-body muscle mass using D3-Creatine (D3-Cr), measured in urine at weeks 6, 12, 18 and 24 postpartum. Using a creatine-tracer measure of muscle mass, Urine D3-creatine and D3-creatinine and unlabelled creatine and creatinine will be measured by liquid chromatography/mass spectrometry, which will allow the calculation of total body creatine pool size and muscle mass.

We intend to estimate muscle breakdown using D3-3-methylhistidine (D3-3MH), measured in urine at weeks 12 and 18 postpartum. Isotopic enrichment of D3-3MH in urine will be measured by gas chromatography/mass spectrometry, which will allow the calculation of muscle protein breakdown.