The Validity and Reliability of Two Commercially Available Load Sensors for Clinical Strength Assessment

Abstract

Objective: Handheld dynamometers are common tools for assessing/monitoring muscular strength and endurance. Health/fitness Bluetooth load sensors may provide a cost-effective alternative; however, research is needed to evaluate the validity and reliability of such devices. This study assessed the validity and reliability of two commercially available Bluetooth load sensors (Activ5 by Activbody and Progressor by Tindeq).

Methods: Four tests were conducted on each device: stepped loading, stress relaxation, simulated exercise, and hysteresis. Each test type was repeated three times using the Instron ElectroPuls mechanical testing device (a gold-standard system). Test-retest reliability was assessed through intraclass correlations. Agreement with the gold standard was assessed with Pearson's correlation, interclass correlation, and Lin's concordance correlation.

Results: The Activ5 and Progressor had excellent test-retest reliability across all four tests (ICC(3,1) ≥ 0.999, all p ≤ 0.001). Agreement with the gold standard was excellent for both the Activ5 (ρ ≥ 0.998, ICC(3,1) ≥ 0.971, ρc ≥ 0.971, all p's ≤ 0.001) and Progressor (ρ ≥ 0.999, ICC(3,1) ≥ 0.999, ρc ≥ 0.999, all p's ≤ 0.001). Measurement error increased for both devices as applied load increased.

Conclusion: Excellent test-retest reliability was found, suggesting that both devices can be used in a clinical setting to measure patient progress over time; however, the Activ5 consistently had poorer agreement with the gold standard (particularly at higher loads).

Keywords: evaluation studies; hand-held dynamometry; muscle testing; sensor characterization; validity and reliability check.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1

Schematic of the testing set-up using the universal testing machine for loading the (A) ActivBody Activ5 in compression; and (B) Tindeq Progressor in tension.

Figure 2

Loading profiles of the ActivBody Activ5 compared to the gold standard (Instron) for (A) Stepped Load Test; (B) Stress Relaxation Test; (C) Simulated Exercise Test; and (D) Hysteresis Test. Additionally, loading profiles of the Tindeq Progressor compared to the gold standard (Instron) for (E) Stepped Load Test; (F) Stress Relaxation Test; (G) Simulated Exercise Test; and (H) Hysteresis Test.

Figure 3

Mean force values across three testing repetitions of each test type comparing the force applied by the gold standard (Instron) against the force measured by the ActivBody Activ5 for (A) Stepped Load Test; (B) Stress Relaxation Test; (C) Simulated Exercise Test; and (D) Hysteresis Test. Additionally, force applied by the gold standard (Instron) against the force measured by the Tindeq Progressor for (E) Stepped Load Test; (F) Stress Relaxation Test; (G) Simulated Exercise Test; and (H) Hysteresis Test. The identity line indicating a perfect linear relationship is also shown.

Figure 4

Relation between the force measured by each device and the force applied by gold standard (Instron) for the stepped loadings test. (A) The ActivBody Activ5 was tested to 10 different loads over the entire loading range; (B) The Tindeq Progressor was tested at 11 different loads. Reported data at each force level correspond to 5 s of measurement when force plateaued at each test load. For both the absolute and relative difference columns, values denote applied force minus measured force. The best-fitting line is also displayed for reference.

Figure 5

Stress relaxation effects for (A) ActivBody Activ5; and (B) Tindeq Progressor. Transparent regions denote isolated 14 s hold.