Are luggage scales a viable alternative to hand-held dynamometers for the measurement of shoulder scaption strength?

Background: The accurate and reliable measurement of muscle strength is a valuable tool in most medical practices. The use of dynamometers allows for objective muscle strength assessment. Even so, dynamometry has its limitations due to increased cost and inconvenience in the clinic. Isokinetic dynamometers, the gold standard, are typically very large and expensive. However, smaller hand-held dynamometers are a cheaper and more efficient alternative. Hand-held dynamometers have been shown to demonstrate comparable reliability to the more expensive isokinetic dynamometers, despite their reduced cost and ease of use. Even though hand-held dynamometers are cheaper and more convenient to use in the clinical setting, their price tag is still burdensome for most medical practices, commonly costing $1000 or more. The aim of this study is to assess the reliability of luggage scales vs. dynamometers for measuring shoulder scaption strength.

Methods: One hand-held dynamometer was compared to two luggage scales using a set-up intended to mimic clinical testing. The set-up consisted of each device being tethered to the floor with the opposite end tied to a length of paracord that had been placed through a shoulder-height pulley and fastened to a flat plate used to hold the weight. In total, ten trials were completed, where a 2.3 kg (5 lb), 4.5 kg (10 lb), and 11.3 kg (25 lb). weight was measured by each device. Analysis of variance was used to compare the numerical data for the three groups.

Results: Our results indicate that there were no significant differences in the force measurements between each device ( = .99). The average force measurements between the three dynamometers were: 2.3 kg trial: 2.3 kg, 2.4 kg, and 2.2 kg; 4.5 kg trial: 4.5 kg, 4.6 kg, and 4.5 kg ; and 11.3 kg trial: 11.4 kg, 11.3 kg, and 11.4 kg. for the digital dynamometer, digital luggage scale, and the analog luggage scale, respectively. Subgroup analysis showed there was also no difference in force measurements between the 3 devices for the 2.3 kg, 4.5 kg, and 11.3 kg. trials ( = .14,  = .49, and  = .40, respectively).

Conclusion: Our data demonstrates that two inexpensive luggage scales showed no statistically significant differences in measurements compared to an expensive hand-held dynamometer. Utilization of luggage scales to measure shoulder scaption strength should yield similar results to handheld dynamometers. This may be an alternative, objective measure of manual muscle strength that is both efficient and economical.