Author(s): GALLINA, A., HUANG, M., MEREDITH, E., Institution: UNIVERSITY OF BIRMINGHAM, Country: UNITED KINGDOM, Abstract-ID: 1204

INTRODUCTION:
Jump height is often considered a key outcome measure in sport performance and rehabilitation, but its measurement in practice relies on the availability of specialized equipment [1]. Smartphone sensors may be a low-cost, widely-available alternative to characterize motor performance in clinics and remotely [2]. We sought to determine whether time of flight estimated using smartphone accelerometer is valid when compared with force platform, reliable between laboratory and home sessions, and whether it can detect changes in performance due to acute pain and fatigue.
METHODS:
Twenty healthy participants (20.6 years old, 6 males) participated in one laboratory session and two remote, unsupervised session. In the laboratory participants performed: 1) five maximal countermovement jumps; 2) five maximal countermovement jumps while experiencing during acute knee pain, induced by means of electrical stimulation at an intensity that induced a perceived pain of 5 out of 10 [3]; 3) a 30s continuous jump test. Participants then performed five countermovement jumps at home, 3-5 and 10-12 days after the laboratory session. Two force platforms were used to collect ground reaction forces in the laboratory. Participants held their own smartphone on their chest and collected acceleration data using the Phyphox application [4]. The time of flight during the jumps was calculated as the time when the ground reaction forces were less than 50N, and when the vertical acceleration was higher than -1 m/s2. Validity and reliability between force plate and smartphone estimates were estimated using Intraclass Correlation Coefficient and T-tests, whereas the effect of acute pain and fatigue was estimated using paired T-tests.
RESULTS:
Validity of time of flight estimates obtained from force plates and smartphone accelerometer was excellent (ICC=0.96) despite 25ms larger estimates for smartphones (p<0.001). Between-day reliability was good (ICC=0.87) between the laboratory and the first home session, and excellent between the two home sessions (ICC=0.93), with no bias in either case (p>0.08). Time of flight decreased during experimental pain (force platform: -3.2%, p=0.001; smartphone: -2.5%, p=0.029) and when comparing the first and last five jumps during the 30s continuous jump test (force platform: -16.8%, p<0.001; smartphone: -13.7%, p<0.001).
CONCLUSION:
Time of flight estimated using smartphone accelerometer is valid compared to force plates, reliable between days and in different environments, and sensitive to changes in performance due to fatigue and pain. The use of the participants’ own smartphones, the performance of the task at home unsupervised, and the fact that participants held the smartphone instead of needing a harness, demonstrates the ecological validity of the proposed approach. Future work should assess the usefulness of this technology in practice.

1. Dutaillis, MSSE 2024;56:181-92
2. Devecchi, PLoS ONE 2023;18:11
3. Gallina, J Physiol 2021;599:2401-17
4. Staacks, Phys Educ 2018;045009