Within and between-day variation and associations of symptoms in Long Covid: Intensive longitudinal study.

BACKGROUND: People with Long Covid (Post Covid-19 Condition) describe multiple symptoms which vary between and within individuals over relatively short time intervals. We aimed to describe the real-time associations between different symptoms and between symptoms and physical activity at the individual patient level. METHODS AND FINDINGS: Intensive longitudinal study of 82 adults with self-reported Long Covid (median duration 12-18 months). Data collection involved a smartphone app with 5 daily entries over 14 days and continuous wearing of a wrist accelerometer. Data items included 7 symptoms (Visual Analog Scales) and perceived demands in the preceding period (Likert scales). Activity was measured using mean acceleration in the 3-hour periods preceding and following app data entry. Analysis used within-person correlations of symptoms pairs and both pooled and individual symptom networks derived from graphical vector autoregression. App data was suitable for analysis from 74 participants (90%) comprising 4022 entries representing 77.6% of possible entries. Symptoms varied substantially within individuals and were only weakly autocorrelated. The strongest between-subject symptom correlations were of fatigue with pain (partial coefficient 0.5) and cognitive difficulty with light-headedness (0.41). Pooled within-subject correlations showed fatigue correlated with cognitive difficulty (partial coefficient 0.2) pain (0.19) breathlessness (0.15) and light-headedness (0.12) but not anxiety. Cognitive difficulty was correlated with anxiety and light-headedness (partial coefficients 0.16 and 0.17). Individual participant correlation heatmaps and symptom networks showed no clear patterns indicative of distinct phenotypes. Symptoms, including fatigue, were inconsistently correlated with prior or subsequent physical activity: this may reflect adjustment of activity in response to symptoms. Delayed worsening of symptoms after the highest activity peak was observed in 7 participants. CONCLUSION: Symptoms of Long Covid vary within individuals over short time scales, with heterogenous patterns of symptom correlation. The findings are compatible with altered central symptom processing as an additional factor in Long Covid.

The relationship between physical activity and severity of COVID-19 symptoms in non-hospitalized individuals.

BACKGROUND: The study explored the relationship between physical activity (PA) behaviour and severity of symptoms in people infected by coronavirus disease 2019 (COVID-19). METHODS: Five hundred and thirty-three people [16% males, mean age: 45 ± 11 years, body mass index (BMI): 23.3 ± 20] took part in the study. All participants were post-COVID-19 infection. An online questionnaire was used to gather data on; participants demographics, comorbidities and treatment, symptomatology of COVID-19, quality of life (QoL) and pre- and post-COVID-19 infection PA. RESULTS: Logistic regression revealed that only a high BMI (>25) increased the severity of (odds ratio 1.01; 95% confidence interval, 0.99-1.03) symptoms from none to mild-to-moderate. Weekly PA behaviour (min/week) did not affect the primary outcome (symptom severity) as a predictor variable and neither differ (P > 0.05) between symptomatology for both moderate (no symptoms: 181.3 ± 202.1 vs. mild-to-moderate symptoms: 173 ± 210.3) and vigorous (no symptoms: 89.2 ± 147 vs. mild-to-moderate symptoms: 88.9 ± 148.3) PA. QoL (i.e. mobility, self-care, usual activities, pain/discomfort, anxiety/depression and perceived health) was significantly (P < 0.05) worse post-COVID-19 infection. CONCLUSIONS: Our findings did not present an association between PA levels and mild-to-moderate COVID-19 symptoms. However, all participants exceeded the lower limit of the World Health Organization recommended, adult PA dose. This might explain the lack of PA effect, on mild-to-moderate symptoms post-COVID-19 infection. Future studies should explore the effects of PA levels in more severe cases (e.g. hospitalizations) and assess the effectiveness of PA to reduce hospitalizations, and mortality rates as a result of COVID-19 infection.

Relay exchanges in elite short track speed skating.

In short track speed skating, the relay exchange provides an additional strategic component to races by allowing a team to change the skater involved in the pack race. Typically executed every 1½ laps, it is the belief of skaters and coaches that during this period of the race, time can be gained or lost due to the execution of the relay exchange. As such, the aim of this study was to examine the influence of the relay exchange on a team's progression through a 5000 m relay race. Using data collected from three World Cup relay events during the 2012-2013 season, the time taken to complete the straight for the scenarios with and without the relay exchange were compared at different skating speeds for the corner exit prior to the straight. Overall, the influence of the relay exchange was found to be dependent on this corner exit speed. At slower corner exit speeds (12.01-13.5 m/s), relay exchange straight times were significantly faster than the free skating scenario (P < 0.01). While at faster corner exit speeds (14.01-15 m/s), straight times were significantly slower (P < 0.001). The findings of this study suggest that the current norm of executing relay exchanges every 1½ laps may not be optimal. Instead, varying the frequency of relay exchange execution throughout the race could allow: (1) time to be gained relative to other teams; and (2) facilitate other race strategies by providing an improved opportunity to overtake.

Effect of tennis racket parameters on a simulated groundstroke.

Composite materials have given manufacturers the freedom to develop a broad range of tennis rackets, allowing them to change key parameters such as the structural stiffness, mass, and position of the balance point. The aim of this research was to determine how changing these parameters could affect ball resultant rebound velocity and spin for a simulated groundstroke. A finite element model of a freely suspended racket and strings was used to determine the effect of racket parameters for oblique spinning impacts at a range of locations on the stringbed. The finite element simulations were conducted in the laboratory frame of reference, where the ball is projected onto an initially stationary racket. The mean rebound velocity of the ball was 9% higher for a structurally stiff racket, 37% higher for a heavy racket, and 32% higher for a head-heavy racket. In addition, the mean rebound topspin of the ball was 23% higher for a heavy racket and 21% higher for a head-heavy racket. Therefore, in relation to a groundstroke with an impact location away from the node, the rebound velocity of the ball is likely to increase with the structural stiffness of a racket. The effect of changing the mass and position of the balance point is more complex, as it is dependent on the relationship between the transverse moment of inertia and maximum pre-impact swing velocity.