Trunk Endurance Testing in Low Back Rehabilitation: What Plank, Side Plank, and Sorenson Tell You

Trunk endurance testing sits at the intersection of clinical assessment and exercise prescription for low back pain. While subjective strength tests dominate UK physiotherapy practice, objective endurance measures provide quantifiable data that can guide treatment decisions and track recovery progress. The plank, side plank, and Sorenson tests offer standardised protocols that translate directly into therapeutic exercise selection.

Understanding what these tests actually measure—and how to interpret their results—transforms them from simple exercises into clinical decision-making tools. Each test reveals different aspects of trunk stability and muscular endurance that influence both pain patterns and functional capacity in patients with low back disorders.

The Clinical Case for Trunk Endurance Testing

Low back pain affects movement patterns through both pain avoidance and genuine muscular dysfunction. Research demonstrates that exercise therapy consistently outperforms passive interventions for chronic low back pain (Hayden et al., 2021), but the challenge lies in selecting appropriate exercises and monitoring progression objectively.

Trunk endurance testing addresses this clinical need by providing baseline measurements that inform exercise prescription. Unlike one-repetition maximum testing, endurance protocols better reflect the sustained muscular demands of daily activities. The ability to maintain trunk stability over time correlates more closely with functional capacity than peak strength measurements.

The three core endurance tests each target different components of trunk stability:

• Plank test: Anterior trunk endurance and global core stability
• Side plank test: Lateral trunk endurance and quadratus lumborum function
• Sorenson test: Posterior trunk endurance and erector spinae capacity

These measurements provide objective data points that remove guesswork from exercise progression. Rather than relying on subjective reports of effort or perceived exertion, clinicians can track specific time-based improvements and identify muscular imbalances between planes of movement.

Plank Test Protocol and Clinical Interpretation

The standard plank test requires patients to maintain a prone position supported on forearms and toes, with the body forming a straight line from head to heels. The test ends when the patient can no longer maintain proper form—typically marked by hip sagging, excessive lordosis, or trembling that compromises position.

Proper execution demands consistent monitoring of form rather than simply timing duration. Key form criteria include neutral spine alignment, engaged abdominal muscles, and steady breathing throughout the hold. The test terminates at the first loss of proper position, not when the patient reports fatigue.

Clinical interpretation relies on normative data and bilateral comparison. Healthy adults typically maintain plank position for 60-120 seconds, with significant variation based on age, fitness level, and training history. More relevant for rehabilitation is the relationship between anterior endurance and the patient's functional demands.

Plank test results guide initial exercise prescription in several ways:

• Duration under 30 seconds indicates significant trunk weakness requiring modified exercises
• 30-60 seconds suggests adequate strength for progressive loading
• Over 90 seconds may indicate readiness for advanced stability challenges
• Form breakdown patterns reveal specific muscular weaknesses or compensatory strategies

Progressive retesting every 2-4 weeks provides objective evidence of improvement and guides exercise advancement. This data-driven approach eliminates the subjectivity inherent in asking patients to rate their own strength or stability.

Side Plank Assessment and Lateral Stability

Side plank testing evaluates lateral trunk endurance, primarily targeting the quadratus lumborum, internal obliques, and transverse abdominis. The test position involves lying on the side, supporting body weight on one forearm and the side of one foot, maintaining a straight line from head to feet.

Bilateral testing is essential, as lateral trunk endurance often shows significant asymmetries that correlate with pain patterns and movement dysfunction. Most patients demonstrate 10-20% differences between sides, but disparities exceeding 25% warrant targeted intervention for the weaker side.

The side plank test reveals compensatory patterns that other assessments might miss. Common form breakdowns include hip hiking, forward rotation of the trunk, and knee dropping toward the floor. Each pattern indicates specific muscular weaknesses or motor control deficits that influence exercise selection.

Clinical decision-making based on side plank results includes:

1. Asymmetry identification: Differences exceeding 15 seconds between sides indicate targeted strengthening needs
2. Progression readiness: Bilateral holds exceeding 45 seconds suggest readiness for loaded exercises
3. Form breakdown analysis: Specific compensation patterns guide corrective exercise selection
4. Functional correlation: Poor lateral endurance often correlates with difficulties in single-leg stance and dynamic activities

The relationship between side plank performance and functional activities makes this test particularly relevant for patients returning to sports or physically demanding occupations. Lateral trunk endurance directly impacts activities involving unilateral loading, rotation, and dynamic balance challenges.

Sorenson Test and Posterior Chain Assessment

The Sorenson test evaluates posterior trunk endurance by measuring how long patients can maintain horizontal extension while prone with their trunk unsupported beyond the edge of a treatment table. This position primarily challenges the erector spinae, multifidus, and gluteal muscles.

Proper test execution requires careful positioning and safety considerations. The patient lies prone with the anterior superior iliac spines at the table edge, arms crossed over the chest, and legs secured by the examiner or strapping. The test measures the time until the patient can no longer maintain a horizontal position.

Sorenson test results provide insight into posterior chain endurance that complements anterior and lateral assessments. This comprehensive view of trunk stability reveals patterns of weakness that single-plane testing might miss. Research consistently links poor posterior trunk endurance with increased low back pain risk and delayed recovery (Ahmadnezhad et al., 2020).

Clinical interpretation focuses on both absolute values and relative performance compared to other endurance tests. Healthy adults typically maintain the Sorenson position for 60-180 seconds, with considerable individual variation. More clinically relevant is the ratio between posterior endurance and anterior/lateral measurements.

Key clinical applications include:

• Baseline establishment: Initial testing provides objective starting point for rehabilitation
• Exercise prescription: Results guide selection of posterior chain strengthening exercises
• Progress monitoring: Regular retesting tracks improvement and guides progression
• Return-to-activity decisions: Minimum thresholds help determine readiness for increased loading

The Sorenson test also reveals compensatory strategies that patients develop to manage low back pain. Common adaptations include excessive hip flexor tension, altered breathing patterns, and early fatigue patterns that provide insights into underlying dysfunction.

Integrating Results into Treatment Planning

The true clinical value of trunk endurance testing emerges when results from all three tests are analysed together. This comprehensive assessment reveals patterns of weakness, asymmetries, and compensatory strategies that guide individualised treatment planning.

Balanced endurance across all three planes suggests good trunk stability and readiness for progressive loading. Significant imbalances between tests indicate specific weaknesses requiring targeted intervention. For example, poor Sorenson performance with adequate plank scores suggests posterior chain weakness despite reasonable anterior stability.

Treatment planning based on endurance testing results should follow a logical progression:

1. Address significant weaknesses first: Target the plane showing the greatest deficit
2. Build balanced endurance: Progress all planes systematically rather than focusing on strengths
3. Monitor ratios: Maintain reasonable balance between anterior, lateral, and posterior endurance
4. Progress systematically: Use objective improvements to guide exercise advancement

Integration with other clinical interventions enhances the effectiveness of endurance-based rehabilitation. Exercise therapy combined with manual therapy approaches shows superior outcomes for chronic low back pain compared to either intervention alone (Narenthiran et al., 2025). Trunk endurance testing provides the objective foundation for selecting and progressing the exercise component.

The testing protocols also support patient education and engagement. Objective measurements help patients understand their current capacity and track meaningful improvements over time. This data-driven approach often increases adherence to exercise programs by providing concrete evidence of progress.

Implementation in Clinical Practice

Successful implementation of trunk endurance testing requires standardised protocols, consistent measurement techniques, and systematic documentation. Each test should be performed using identical positioning, timing methods, and termination criteria to ensure reliable results.

Documentation should capture both quantitative results and qualitative observations. Recording test duration provides the objective measurement, while noting form breakdown patterns and compensatory strategies adds clinical context that guides exercise selection. This comprehensive approach maximises the clinical utility of testing time.

Regular retesting schedules maintain momentum and provide objective feedback on treatment effectiveness. Most patients benefit from retesting every 2-4 weeks during active rehabilitation, with longer intervals as function improves and treatment transitions to maintenance.

Staff training ensures consistent test administration and interpretation across all clinicians. Standardised protocols reduce measurement error and improve the reliability of results for clinical decision-making. This consistency is particularly important in multi-clinician practices where patients may see different therapists.

For practices seeking to implement objective measurement protocols, trunk endurance testing offers a practical starting point that requires minimal equipment while providing valuable clinical data. These assessments integrate seamlessly into existing examination procedures and directly inform exercise prescription decisions.

The transition from subjective assessment to objective measurement represents a fundamental shift toward evidence-based rehabilitation. Trunk endurance testing provides the foundation for this transition by offering reliable, clinically relevant data that improves both treatment planning and patient outcomes.

References

1. Hayden JA, Ellis J, Ogilvie R et al. Some types of exercise are more effective than others in people with chronic low back pain: a network meta-analysis. Journal of physiotherapy. 2021;67(4):252-262. PubMed
2. Ahmadnezhad L, Yalfani A, Gholami Borujeni B. Inspiratory Muscle Training in Rehabilitation of Low Back Pain: A Randomized Controlled Trial. Journal of sport rehabilitation. 2020;29(8):1151-1158. PubMed
3. Narenthiran P, Granville Smith I, Williams FMK. Does the addition of manual therapy to exercise therapy improve pain and disability outcomes in chronic low back pain: A systematic review. Journal of bodywork and movement therapies. 2025;42:146-152. PubMed