Number of subjects and motor units (MU), motor unit discharge rate (MUDR) and relative force and sEMG levels of soleus (SOL) and gastrocnemius medialis (GM) in different conditions.

<p>Force and sEMG levels are calculated relative to isometric MVC. *: significantly larger than in lower force level. ^† : significantly smaller than in CON. ^‡ : significantly smaller than in ECC (P<0.05).</p

Relative muscle activity in different trials. sEMG levels of soleus (A) and gastrocnemius medialis (B) at different force levels in eccentric (ECC), isometric (ISO) and concentric (CON) contractions.

<p>sEMG is expressed relative to maximal isometric contraction (MVC). Significant differences between conditions and force-levels: *  = p<.05, **  = p<.01, ***  = p<.001.</p

Motor unit discharge rate (1/s; X±SD) at different relative force levels (%MVC) in eccentric (ECC), isometric (ISO) and concentric (CON) contractions.

<p>Significant differences between conditions and force-levels: *  = p<.05, **  = p<.01, ***  = p<.001.</p

Examples of ISO, CON and ECC trials from one subject at 10% MVC.

<p>TOP: Cursors 1 and 2 mark the beginning and end of analysis, respectively. In dynamic contractions Cursor 1 is 200 ms prior and Cursor 2 200 ms after the angle crosses the angle of the ISO trial, as indicated by the horizontal cursor. BOTTOM: 400 ms close-ups of the wire EMG signal of each trial.</p

Discharge rates of motor units that could clearly be recognized in at least two of the three contraction types at 10 (solid line), 20 (dashed line) and 40% of MVC (dotted line).

<p>Discharge rates of motor units that could clearly be recognized in at least two of the three contraction types at 10 (solid line), 20 (dashed line) and 40% of MVC (dotted line).</p

Clusters of adolescent physical activity tracker patterns and their associations with physical activity behaviors in Finland and Ireland:cross-sectional study

Background: Physical activity trackers (PATs) such as apps and wearable devices (eg, sports watches, heart rate monitors) are increasingly being used by young adolescents. Despite the potential of PATs to help monitor and improve moderate-to-vigorous physical activity (MVPA) behaviors, there is a lack of research that confirms an association between PAT ownership or use and physical activity behaviors at the population level. Objective: The purpose of this study was to examine the ownership and use of PATs in youth and their associations with physical activity behaviors, including daily MVPA, sports club membership, and active travel, in 2 nationally representative samples of young adolescent males and females in Finland and Ireland. Methods: Comparable data were gathered in the 2018 Finnish School-aged Physical Activity (F-SPA 2018, n=3311) and the 2018 Irish Children’s Sport Participation and Physical Activity (CSPPA 2018, n=4797) studies. A cluster analysis was performed to obtain the patterns of PAT ownership and usage by adolescents (age, 11-15 years). Four similar clusters were identified across Finnish and Irish adolescents: (1) no PATs, (2) PAT owners, (3) app users, and (4) wearable device users. Adjusted binary logistic regression analyses were used to evaluate how PAT clusters were associated with physical activity behaviors, including daily MVPA, membership of sports clubs, and active travel, after stratification by gende