**Brief Summary**

Lumbar radicular pain arising from intervertebral disc herniation is commonly managed with a caudal epidural steroid injection (CESI), a minimally invasive procedure that delivers anti-inflammatory medication to the sacral hiatus. Although CESI affords short-term analgesia, a sizable proportion of patients continue to experience pain-related disability and diminished quality of life, underscoring the need for optimised post-injection rehabilitation.

This single-centre, three-arm, parallel-group randomised controlled trial will evaluate the comparative efficacy of two evidence-informed exercise paradigms-moderate-intensity aerobic training and progressive lumbopelvic stabilisation-when each is superimposed upon a standard physiotherapy package of heat, therapeutic ultrasound and transcutaneous electrical nerve stimulation (TENS). Forty-two adults (18-70 years) with MRI-confirmed lumbar disc herniation who have undergone CESI at Çankırı State Hospital will be randomly allocated (1:1:1) to one of the following six-week interventions, initiated two weeks post-injection and delivered thrice weekly under physiotherapist supervision:

1. Conventional physiotherapy alone (heat + ultrasound + TENS).
2. Conventional physiotherapy plus aerobic exercise (treadmill walking at 55-80 % of age-predicted maximal heart rate with structured warm-up/cool-down).
3. Conventional physiotherapy plus core-stabilisation exercise (phased activation of deep trunk musculature progressing to dynamic tasks on unstable surfaces).

Primary end-points are pain intensity (10 cm Visual Analogue Scale) and back-specific disability (Oswestry Disability Index). Secondary end-points include generic health-related quality of life (SF-12) and lumbar proprioceptive body awareness (Fremantle Back Awareness Questionnaire). Outcomes will be captured at baseline, post-intervention (6 weeks) and at 3- and 6-month follow-up to ascertain both immediate and sustained effects.

Study Question Does adjunctive aerobic or core-stabilisation exercise confer superior reductions in pain and disability, and greater gains in quality of life and body awareness, compared with conventional physiotherapy alone in adults following CESI for lumbar disc herniation?

It is hypothesised that both exercise approaches will yield clinically and statistically superior outcomes relative to standard care, with stabilisation training providing the most durable functional benefits. Findings are expected to refine post-CESI rehabilitation algorithms and inform evidence-based clinical guidance for physiotherapists managing lumbar disc pathology.

Scientific Rationale and Background Caudal epidural steroid injection (CESI) is widely employed to attenuate lumbosacral radicular pain by delivering glucocorticoids into the sacral hiatus, thereby diminishing local biochemical inflammation around the affected nerve roots. While CESI frequently yields rapid analgesia, pain recurrence and activity limitation are common within three to six months, indicating that pharmacological attenuation of inflammation alone is insufficient to restore neuromuscular control and functional capacity. Emerging evidence suggests that structured exercise commenced shortly after CESI can exploit the "analgesic window" to retrain motor patterns, enhance spinal stability, and improve cardiovascular fitness-yet the optimal exercise paradigm remains unclear. Aerobic conditioning may promote anti-inflammatory myokine release and general de-conditioning reversal, whereas lumbopelvic stabilisation targets segmental control deficits and proprioceptive impairment-both recognised contributors to chronicity in lumbar disc pathology.

Study Design and Setting This is a single-centre, prospective, three-arm, parallel-group, superiority randomised controlled trial conducted at the Department of Physiotherapy, Çankırı State Hospital, Türkiye. Allocation (1:1:1) is computer-generated with permuted blocks of variable size; assignments are sealed in sequentially numbered opaque envelopes by an independent statistician to ensure allocation concealment. Outcome assessors and data analysts are blinded to group assignment. Interventions are delivered in a dedicated physiotherapy gymnasium under the supervision of senior musculoskeletal physiotherapists trained in study procedures.

Intervention Logic

Each participant receives a two-week "wash-in" period following CESI to permit stabilisation of acute pharmacodynamic effects. Thereafter, three arms are implemented over six weeks (18 supervised sessions):

1. Conventional Physiotherapy (control) - superficial moist heat (20 min, 70 °C hydrocollator packs), continuous ultrasound (1 MHz, 1.0 W cm-², 5 min), and biphasic TENS (100 Hz, 100 µs, 20 min).

2. Conventional Physiotherapy + Aerobic Exercise - identical modality package followed by treadmill walking at 55-80 % age-predicted HR_max with 5 min warm-up, 10-25 min load (weekly 5 % progression), and 5 min cool-down. Heart rate is telemetrically monitored; intensity is titrated using the Borg CR-10 scale and Tanaka equation (208-0.7·age).

3. Conventional Physiotherapy + Core-Stabilisation Exercise - modality package followed by a phased stabilisation protocol:

   • Phase I: isolated transversus abdominis and multifidus activation in supine/prone using pressure biofeedback (2 weeks).
   • Phase II: functional co-contraction with limb movements in quadruped, sitting, and standing (2 weeks).
   • Phase III: dynamic tasks on unstable surfaces (Swiss-ball, BOSU) incorporating resistance bands (2 weeks).

Progression criteria include pain ≤3/10 on VAS and flawless technique for ≥10 repetitions; repetitions, load, or surface instability are advanced by ~10 % weekly.

All participants receive a standardised education booklet on spine-sparing strategies and are advised to maintain normal activities.

Sample Size Justification Using an anticipated between-group effect size of d = 1.0 for pain reduction-derived from prior work on CESI-augmented exercise (Cohen's f = 0.5)-42 participants (14 per arm) provide 80 % power (α = 0.05, two-sided) to detect clinically important differences, allowing for 25 % attrition.

Data Management and Statistical Plan Data are entered into REDCap with double-entry verification. The primary analysis follows the intention-to-treat principle, employing linear mixed-effects models with random intercepts for participants, fixed effects for group, time, and their interaction, and baseline score as covariate. Missing data will be handled using restricted maximum likelihood under a missing-at-random assumption; sensitivity analyses will include multiple imputation. Secondary outcomes will be analysed similarly with Bonferroni-adjusted confidence intervals. Effect sizes (Hedges g) and minimal clinically important differences will be reported.

Safety Monitoring Adverse events-including exacerbation of radicular pain, hemodynamic instability during aerobic sessions, or procedure-related complications-are recorded at each visit. An independent physician adjudicates seriousness and relatedness; criteria for withdrawal include VAS ≥ 7 persisting >48 h or cardiovascular red-flags according to American College of Sports Medicine guidelines. A Data Safety Monitoring Sub-committee reviews unblinded safety reports quarterly.

*Knowledge Translation* Results will inform evidence-based guidelines on post-CESI rehabilitation, disseminated via peer-reviewed publication, conference presentation, and integration into continuing professional development modules for physiotherapists. De-identified datasets and analytic code will be deposited in an open repository within 12 months of primary outcome publication, aligning with FAIR data principles and UK Research Councils' open-science policy.

In summary, this rigorously designed trial seeks to delineate whether adjunctive aerobic or motor-control-oriented exercise offers superior and durable benefits over conventional modalities alone in the critical post-injection period for patients with lumbar disc herniation, thereby refining best-practice rehabilitation pathways.

Inclusion Criteria:

• Age 18 to 70 years.
• MRI-confirmed lumbar intervertebral disc herniation.
• Has received a caudal epidural steroid injection (CESI) within the past 2 weeks at Çankırı State Hospital.
• Low-back or leg pain intensity ≥ 3 cm on a 10-cm Visual Analogue Scale after the injection.
• Medically cleared for moderate aerobic and core-stabilisation exercise (no cardiac or orthopaedic contraindications).
• Able to attend supervised physiotherapy three times per week for six weeks.
• Willing and able to give written informed consent and to comply with study procedures.
• Sufficient Turkish literacy (minimum primary-school education) to complete questionnaires.

Exclusion Criteria:

• Uncontrolled systemic disease (e.g., poorly controlled diabetes mellitus, congestive heart failure, active hepatitis C or other significant liver disease).
• Neurological red flags such as myelopathy or cauda equina syndrome.
• Previous lumbar spine surgery at the affected disc level.
• Current pregnancy or planning pregnancy during the study period.
• Severe musculoskeletal, cardiovascular, or respiratory condition that precludes safe exercise participation.
• Use of systemic corticosteroids or opioid analgesics that cannot be stabilised for the duration of the trial.
• Ongoing litigation or workers' compensation claim related to low-back pain.
• Inability to communicate effectively with study staff or to follow instructions.

A de-identified participant-level dataset and accompanying data dictionary will be deposited in an open-access repository (e.g., Open Science Framework) within 12 months of publication of the primary results, accessible to qualified researchers under a CC-BY license.

The treating physiotherapists and participants cannot be blinded because the nature of the exercise programmes is overt. However, (i) outcome assessors who perform all baseline and follow-up measurements and (ii) the trial statistician responsible for primary analyses will remain unaware of group allocation. Randomisation codes are stored in sealed, opaque envelopes by a study coordinator not involved in assessment or analysis, and participants are reminded not to disclose their exercise group during evaluations.