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Validation Studies
Validation Studies
The DAVID equipment has been subjected to several validation studies. In this overview you will find the most relevant studies and a complete list of all studies conducted so far. Ongoing research is being conducted on the validation of our equipment. When the studies are published they will be included on this page.
Feasibility and Reliability of Functional Muscle Tests in Lung Transplant Recipients
After lung transplantation, patients often experience severe muscle weakness and reduced endurance. Early detection and monitoring of these deficits are crucial for effective rehabilitation. This study evaluated whether simple functional muscle tests are feasible, reliable, and useful in tracking recovery.
Objective
To examine if three functional tests — back extension strength, handgrip strength, and back extension endurance — are practical to perform, reproducible across time, and sensitive to rehabilitation progress in lung transplant recipients.
Method
Participants: 50 lung transplant recipients, both men and women, assessed at hospital discharge, 1–2 days later, and again two to three months into rehabilitation.
Tests performed:
- Maximum isometric back extension strength
- Handgrip strength
- Biering-Sørensen back extension endurance test
- Evaluation: Feasibility (can patients perform it safely?), reliability (consistency across tests), and responsiveness (do results capture improvement after rehab).
Outcomes
Feasibility:
- All patients completed back extension and handgrip strength tests.
- Endurance testing was less feasible early on; some patients lacked the strength or confidence to complete it.
Reliability:
- Back extension and handgrip strength showed excellent reproducibility with minimal measurement error.
- Endurance was moderately reliable but more variable.
Recovery sensitivity:
- Significant gains were seen after rehabilitation: handgrip strength improved by ~44%, back extension strength nearly doubled, and endurance increased more than threefold.
Correlations:
- Strong link between handgrip and back extension strength, making grip strength a potential quick indicator of overall muscle strength.
- Endurance performance did not correlate strongly with strength tests, indicating it measures a different capacity.
Why it Matters
- Back extension and handgrip strength tests are safe, practical, and highly reliable, even in fragile patients shortly after surgery.
- Endurance testing adds value but is better suited later in recovery when patients have regained baseline strength.
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These tests can guide clinicians in tailoring rehabilitation, tracking progress, and ensuring patients regain the physical capacity they need for daily life.
Kienbacher T., Achim-Gunacker G., Pachner M., Kerschan-Schindl K., Gunacker P., Habenicht R., Klepetko W., Jaksch P., Doblhammer S., Ebenbichler G. Feasibility and Reliability of Functional Muscle Tests in Lung Transplant Recipients. American Journal of Physical Medicine & Rehabilitation. Philadelphia; Lippincott, Williams & Wilkins; 2018. Vol. 97(6), pp. 390-396.
Age-Related Test-Retest Reliability of Isometric Trunk Torque in Chronic Low Back Pain
Accurate and repeatable strength testing is essential when assessing patients with chronic low back pain. This study explored whether isometric trunk torque measurements are equally reliable in younger, middle-aged, and older adults, and whether short- and long-term results are consistent.
Objective
To determine the short- and long-term reliability of isometric trunk strength measurements (extension, flexion, rotation) across different age groups in chronic low back pain patients, and to see if factors like pain, motivation, or emotional state influence outcomes.
Method
- Participants: 210 adults with chronic low back pain, aged 18–90, divided into three groups: young (18–39), middle-aged (40–59), and older (60–90).
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Testing schedule:
- Baseline (day 1)
- Short-term retest (1–2 days later)
- Long-term retest (~6 weeks later)
- Measures: Maximum isometric trunk torque (extension, flexion, rotation) using a dynamometer; self-reported pain, feelings, and motivation before testing.
- Analysis: Relative reliability (ICCs), absolute reliability (SEM and smallest real difference), plus group comparisons.
Outcomes
Reliability:
- All age groups showed good to excellent reliability for trunk extension, flexion, and rotation.
- Absolute error was generally low (≤10%), confirming stable measures.
Short- vs long-term:
- Younger and middle-aged groups displayed “learning effects” with strength increases from baseline to retests.
- Older adults had more stable results with less change over time
- Influence of pain or motivation: No significant effects on reliability were observed.
Implications
- Isometric trunk torque testing is feasible and reliable for all age groups, including older adults with chronic low back pain.
- Conducting a second baseline test shortly after the first can reduce learning effects and improve the accuracy of tracking changes.
- Clinicians can interpret improvements beyond the small measurement error as true, meaningful gains in strength.
Kienbacher T., Kollmitzer J., Anders P., Habenicht R., Starek C., Wolf M., Paul B., Mair P., Ebenbichler G. Age-related test-retest reliability of isometric trunk torque measurements in patients with chronic low back pain. Journal of Rehabilitation Medicine. Uppsala; Medical Journals Sweden AB; 2016; 48(10):893-902.
Isometric reliability test
Objective
To investigate the reliability of mobility measurement and isometric strength measurement in David spine devices.
Method
Measurements were performed on three different days by an experienced tester. The time interval between each examination day was 72 hours. Tests were performed with David Spine devices.
Outcome
The isometric strength measurements showed a strong correlation (r=0.94-0.99). Also the correlation in mobility measurements (in those movement direction where it was measured) was strong (r=0.90-0.98).
Denner A. Muskuläre Profile der Wirbelsäule. Berlin, Heidelberg; Springer; 1997. Chapter 7.4, Ergebnisse Eigener Reliabilitäts- und Validitätsuntersuchungen; p. 163–178.
Muscle activity in target muscles in different movement directions of the spine
Objective
To analyze the muscle activity of the target muscles compared to other muscles in David Spine devices.
Methods
EMG was used to test the isolation of target muscles during maximal isometric contraction. In 110 and 130 devices also muscle activation during submaximal dynamic muscle work (70% of 1 RM) was tested.
Outcome
Fixation in David Spine devices seems to effectively activate target muscles and inhibit other muscles.
Denner A. Muskuläre Profile der Wirbelsäule. Berlin, Heidelberg; Springer; 1997. Chapter 7.4, Ergebnisse Eigener Reliabilitäts- und Validitätsuntersuchungen; p. 163–178.
Intra- and inter-tester reliability and reference values for isometric neck strength.
Objective
To determine intra- and inter-tester reliability and age- and sex-specific reference values for isometric neck strength in extension, flexion and lateral flexion in sitting position measured with David 140 device.
Methods
Reliability: Intra-tester reliability was studied in three repeated test trials, with 10 minutes of rest between the measurement series. Inter-tester reliability was studied by repeating the procedure with each of the three test leaders at the same time of the day, on three different occasions, with an interval of one week between test series.
Reference values: One maximal effort for about six to eight seconds was registered in each movement direction for each subject.
Outcome
Intra-tester reliability, for all three test leaders, expressed as the ICC value was 0.94–0.97 for neck strength in extension, flexion, lateral flexion (right/left). Inter-tester reliability among the three test leaders was 0.86–0.95 in the four directions. For all three test leaders, and for almost all directions, measurement one was found to have the highest value. Results show that Intra- and inter-tester reliability of the 140 was very good to excellent.
Peolsson A, ÖBerg B, Hedlund R. Intra- and inter-tester reliability and reference values for isometric neck strength. Physiotherapy Research International 2001;6(1):15-26.
Overview validation studies:
- Häkkinen K, et al. Scientific Evaluation of Specific Loading of the Knee Extensors with Variable Resistance, ‘Isokinetic’ and Barbell Exercises. Med Sport Sci. 1987;26:224-237.
- Häkkinen K, et al. Effects of fatiguing loading with a variable resistance equipment on neural activation and force production of the knee extensor muscles. Electromyogr Clin Neurophysiol. 1988;28(2-3):79-87.
- Denner A. Muskuläre Profile der Wirbelsäule. Berlin, Heidelberg; Springer; 1997. Chapter 7.4, Ergebnisse Eigener Reliabilitäts- und Validitätsuntersuchungen; p. 163–178.
- Denner A. Muskuläre Profile der Wirbelsäule. Berlin, Heidelberg; Springer; 1997. Chapter 7.4, Ergebnisse Eigener Reliabilitäts- und Validitätsuntersuchungen; p. 163–178.
- Kankaanpää M, et al. Lumbar paraspinal muscle fatigability in repetitive isoinertial loading: EMG spectral indices, Borg scale and endurance time. European Journal of Applied Physiology 1997;76(3):236-242.
- Kankaanpää M, et al. Reference change limits of the paraspinal spectral EMG in evaluation of low back pain rehabilitation. Pathophysiology 1998;5(3):217-224.
- Kankaanpää M, et al. Back and hip extensor fatigability in chronic low back pain patients and controls. Archives of Physical Medicine and Rehabilitation 1998;79(4):412-417.
- Taimela S, et al. A submaximal back extension endurance test utilising subjective perception of low back fatigue. Scandinavian Journal of Rehabilitation Medicine 1998;30(2):107-112
- Peolsson A, et al. Intra- and inter-tester reliability and reference values for isometric neck strength. Physiotherapy Research International 2001;6(1):15-26.
- Leinonen V, et al. Impaired Lumbar Movement Perception in Association With Postural Stability and Motor- and Somatosensory-Evoked Potentials in Lumbar Spinal Stenosis. Spine 2002;27(9):975-983.
- Elfving B. Lumbar muscle fatigue and recovery: Evaluation of electromyography in patients with long-term low-back pain and in healthy subjects. Karolinska Institutet. Doctoral Dissertation; 2002.
- Walker S, et al. Kinetic and electromyographic analysis of single repetition constant and variable resistance leg press actions. Journal of Electromyography and Kinesiology 2011;21(2):262-269
- Peltonen H, et al. Neuromuscular responses to different resistance loading protocols using pneumatic and weight stack devices. Journal of Electromyography and Kinesiology 2013;23(1):118-124.
- Kienbacher T, et al. Reliability of isometric trunk moment measurements in healthy persons over 50 years of age. Journal of Rehabilitation Medicine 2014;46(3):241-249.