Difference in racket head trajectory and muscle activity between the standard volley and the drop volley in tennis.

Among tennis coaches and players, the standard volley and drop volley are considered basically similar, but muscles need to be relaxed (deactivation) just at the moment of impact when hitting the drop volley. However, this is not evidence-based. The aim of this study was to clarify racket head trajectory and muscle activity during the drop volley and to compare them with those of the standard volley. We hypothesized that 1) the racket head would move less forward for the drop volley than for the standard volley and 2) the wrist and elbow muscles be relaxed for the drop volley at the time of ball impact. Eleven male college students with sufficient tennis experience volunteered to participate in this study. Wireless EMG sensors recorded activation of the four arm muscles. Each subject performed the standard volley or the drop volley with both a forehand and a backhand from a position near the net. Four high speed video cameras (300 Hz) were set up on the court to measure ball speed and racket head trajectory. Returned ball speed of the drop volley was significantly lower than that of the standard volley (p < 0.05). The racket head moved less forward than in the standard volley, supporting the first hypothesis. Muscle activity of the drop volley, just before and after ball impact for both the forehand and backhand, was lower than that of the standard volley. However, the activity was in the form of a gradual increase as impact time approached, rather than a sudden deactivation (relaxation), which did not support the second hypothesis. For the drop volley, lower muscle activity in the forearm enabled a softer grip and thus allowed a "flip" movement of the racket to diminish the speed of the returned ball.

Axial and peripheral spondyloarthritis triggered by sars-cov-2 infection: a report of two cases.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can show musculoskeletal symptoms such as peripheral arthritis. In rare cases, peripheral arthritis can develop after the resolution of SARS-CoV-2. We present two cases of spondyloarthritis induced by SARS-CoV-2; one case with axial and peripheral spondyloarthritis and the other with peripheral spondyloarthritis. Both cases refer to Lebanese patients who were HLA-B27 positive. These two cases highlight the possible predisposition of HLA-B27 positive patients to the development of spondyloarthritis symptoms triggered by SARS-CoV-2.

Virtual assessments of knee and wrist joint range motion have comparable reliability with face-to-face assessments.

BACKGROUND: There has been increased usage of virtual telerehabilitation approach during the COVID-19 pandemic. It is crucial to establish reliability of conducting virtual assessments for musculoskeletal conditions. OBJECTIVES: This research determined the intra- and interrater reliability of measuring knee and wrist range of motion (ROM) assessed virtually and obtained face-to-face (F2F) using a goniometer (UG) for a student and an experienced examiner. METHOD: Knee and wrist joint ROM for 54 healthy participants was assessed virtually and F2F by a student examiner and an experienced physical therapist. Intra- (virtual vs. UG assessment) and inter-rater (virtual or UG assessment between examiners) reliabilities were examined for all ROM using Intraclass correlation coefficient (ICC). The ICC values were considered good (>0.75) or excellent (>0.90). Bland and Altman plots determined the limits of agreement (LOA) in assessing joint ROM. RESULTS/FINDINGS: Student examiner had good reliability in virtually estimating knee extension (ICC = 0.79), wrist flexion (ICC = 0.82) and wrist extension (ICC = 0.78), whereas the experienced examiner had excellent reliability in virtually estimating all knee and wrist ROM (ICC > 0.90). The LOA in assessing knee and wrist ROM for the student examiner were wider indicating higher disagreement between virtual and UG-obtained ROM in some cases. CONCLUSIONS: Virtual estimation of knee and wrist ROM is a reliable technique, however experience level impacts the precision of measurement. It is suggested that the same examiner conducts all the ROM assessments throughout the clinical course of a patient receiving virtual interventions for knee or wrist pathologies.