FedStale: leveraging stale client updates in federated learning

Federated learning algorithms, such as FedAvg, are negatively affected by data heterogeneity and partial client participation. To mitigate the latter problem, global variance reduction methods, like FedVARP, leverage stale model updates for non-participating clients. These methods are effective under homogeneous client participation. Yet, this paper shows that, when some clients participate much less than others, aggregating updates with different levels of staleness can detrimentally affect the training process. Motivated by this observation, we introduce FedStale, a novel algorithm that updates the global model in each round through a convex combination of "fresh" updates from participating clients and "stale" updates from non-participating ones. By adjusting the weight in the convex combination, FedStale interpolates between FedAvg, which only uses fresh updates, and FedVARP, which treats fresh and stale updates equally. Our analysis of FedStale convergence yields the following novel findings: i) it integrates and extends previous FedAvg and FedVARP analyses to heterogeneous client participation; ii) it underscores how the least participating client influences convergence error; iii) it provides practical guidelines to best exploit stale updates, showing that their usefulness diminishes as data heterogeneity decreases and participation heterogeneity increases. Extensive experiments featuring diverse levels of client data and participation heterogeneity not only confirm these findings but also show that FedStale outperforms both FedAvg and FedVARP in many settings.Comment: 33 pages, 5 figures, preprin

Is the Focal Muscle Vibration an Effective Motor Conditioning Intervention? A Systematic Review

Mechanical vibration, applied to single or few muscles, can be a selective stimulus for muscle spindles, able to modify neuromuscular management, inducing short and long-term effects, are now mainly employed in clinic studies. Several studies reported as treatments with focal vibratory (FVT) can influence neuromuscular parameters also in healthy people. However, the application modalities and the consequent effects are remarkably fragmented. This paper aims to review these studies and to characterize the FVT effectiveness on long-term conditional capacities in relation to FVT characteristics. A systematic search of studies published from 1985 to 2020 in English on healthcare databases was performed. Articles had to meet the following criteria: (1) treatment based on a locally applied vibration on muscle belly or tendon; (2) healthy adults involved; (3) outcomes time analysis enduring for more than 24 h. Twelve studies were found, all of them presented an excellent quality score of 6575%. All selected papers reported positive changes, comparable with traditional long-lasting training effects. Muscle force and power were the most investigated parameters. The after-effects persisted for up to several months. Among the different FV administration modalities, the most effective seems to show a stimulus frequency of 48100 Hz, repeated more times within three-five days on a voluntary contracted muscle

Energy expenditure and perceived exertion during active video games in relation to player mode and gender

Active video games (AVG) increase energy expenditure (EE) with respect to sedentary video games. Although several AVG consoles allow playing in single-player (SP) or multiplayer (MP) mode, few studies investigated differences in relation to game modality in men and women. Therefore, the aim of this study was to evaluate gender-related psycho-physiological responses during Zumba Fitness Rush (ZFR) played in SP vs. MP mode. Twenty-four college students (women: 14, men: 10; age: 24.6±2.0 years; body weight: 60.2±12.5 kg; body height: 167.8±11.5 cm; BMI: 21.2±2.1 kg·m-2) participated in two experimental sessions: SP (a subject playing ZFR alone) and MP (two subjects playing ZFR simultaneously). Heart rate (HR), oxygen consumption (VO2) and EE (MET and kcal∙min-1) were continuously measured and averaged every 10 seconds, while Rating of Perceived Exertion (RPE) was recorded 30 minutes after the end of each session. A two (gender: women vs. men) by two (modality: SP vs. MP) ANOVA for repeated measures was applied. No differences emerged in relation to gender and game mode for %HRmax, VO2, MET, and RPE. Conversely, a main effect (p=.0007) for gender was found in EE, with significantly (p<.004) higher values in men in SP (women: 5.5±0.6 kcal·min-1; men: 8.3±1.4 kcal·min-1) and MP (women: 5.3±0.7 kcal·min-1; men: 7.6±1.9 kcal·min-1). Present findings suggest that ZFR could be classified as a moderate physical activity, proving to be an alternative form to traditional exercise. Although an effect of number of players could be expected, different player modes did not affect EE, probably because the rhythm of the music imposes a time constraint, independently of the presence of other players

Home is the new gym: Exergame as a potential tool to maintain adequate fitness levels also during quarantine

Purpose. With the coronavirus outbreak, the preventive measures include staying at home and isolation, increasing sedentary behaviours and risk for worsening of chronic diseases. To explore alternative forms of home-based physical activity, the study aim was to evaluate physiological (heart rate [HR], respiratory exchange ratio [RER], oxygen consumption [ O2], energy expenditure [EE], metabolic equivalent task [MET]) and psychological (session rating of perceived exertion [sRPE], enjoyment) parameters of real (Zumba® class [ZC]) and exergame (Zumba® Fitness Rush [ZFR]) activities in relation to sex. Methods. Overall, 12 female (age: 24.7 ± 0.9 years) and 8 male (age: 25.3 ± 2.1 years) college students randomly performed 2 experimental 60-min sessions, ZC and ZFR, during which HR (expressed as percentage of individual maximal HR [%HRmax]), O2, RER, MET and EE were measured. After each session, sRPE and Physical Activity Enjoyment Scale (PACES) were used to monitor exercise intensity and enjoyment, respectively. Results. Main effects for sex (p = 0.02) and modality (p &lt; 0.0001) emerged for %HRmax, with women showing higher values than men and ZC showing higher values than ZFR. EE presented main effects for sex (p &lt; 0.0001) and modality (p = 0.0002), with higher values in men and in ZC. Main effect (p = 0.0001) for modality emerged also for O2 and MET, with higher values in ZC regardless of sex. No significant differences were observed for RER, sRPE, or PACES. Conclusions. Although ZC elicited higher cardiovascular and metabolic responses, ZFR, classified as a moderate-to-vigorous activity, could be used to maintain regular physical activity in a safe home environment during the coronavirus crisis