The analysis of motor unit (MU) discharge behavior provides an effective way of assembling information about the generation and control of movement. In this systematic review and meta-analysis, we identified and summarized the literature investigating MU discharge rate and discharge rate variability (CoV-ISI) during voluntary isometric contractions at various force levels. Databases were searched up to January 7, 2025, and a total of 262 studies were included. The meta-means of MU discharge rate and CoV-ISI were estimated and compared across human muscles. The influence of contraction intensity on MU discharge behavior was assessed through linear meta-regressions. At low-to-moderate forces [60% MVC), the tibialis anterior (TA) had the highest mean discharge rate compared with all other muscles, with the soleus maintaining the lowest. Regarding CoV-ISI results at low forces (<30% MVC), the TA had the lowest CoV-ISI values, except in comparison with the vastii. In addition, the vastii had lower CoV-ISI values than the FE, gastrocnemius medialis, and soleus. Contraction intensity was positively associated with the mean discharge rates in all muscles investigated, although some muscles showed steeper slopes than others. Similar results were observed for CoV-ISI meta-regressions, with muscle-specific differences in slope. These findings suggest potential variations in neural control strategies across muscles during force gradation, such as differences in the relative contribution of rate coding to facilitate increasing force demands.

This study examines four tracks (Ts) suitable for handbikes (HBs) in the urban area of Brescia, Italy. WHO physical activity (PA) recommendations challenge kinesiologists to find opportunities to promote exercise in the urban context using HBs. This study aims to characterize T features, assess the physical demands of HB cycling, and promote the use of HBs. Track length, elevation changes, slope, and ascent sections were analyzed. Participants’ physiological engagement during HB cycling was measured. The data were gathered using specialized equipment including a metabolimeter, a power meter, a heart rate monitor, and a cycle computer. Crucially, the findings demonstrate that all four Ts facilitate PA above the recommended threshold (>3 MET) regardless of the speed. The study identifies specific speeds required to achieve vigorous PA (>6 MET) on each T. In summary, this study’s analysis of various tracks reveals their potential to meet PA guidelines, even at a slow pace. Moreover, this research establishes speed thresholds for vigorous PA. This information is valuable for both able-bodied individuals and those with mobility challenges when planning effective exercise routines. Moreover, the findings support municipalities in promoting adapted PA in urban areas, enhancing path usability.

Introduction: E-bikes are being promoted as a mode of transportation that can aid with meeting current physical activity guidelines. This study evaluated exertional intensity associated with E-Biking within the exercise intensity domain framework. We hypothesized that exertional intensity of E-bikes is insufficient to evoke a metabolic demand associated with the minimum intensity needed to improve cardiorespiratory fitness. Methods: Forty-four participants (22 females) of varying activity levels completed two experimental sessions. The first session involved a lab-based ramp-incremental exercise test to determine V̇O _2max , gas exchange threshold (GET), and respiratory compensation point (RCP). The second session involved the completion of two outdoor rides on the same bike equipped with an electrical motor E-bike. The first ride was completed without electrical assistance, while the second was. The power output (PO) and speed were set at an intensity corresponding to ∼10% above GET. Results: As expected, using E-bike assistance resulted in a lower metabolic demand, falling well below GET. While the absolute power output (PO) was different between sexes, relative heart rate (HR) and relative PO were similar between the rides without and with assistance. This suggests that when riding an E-bike, the internal load is similar between sexes. Conclusion: Despite E-bikes facilitate a more active lifestyle and help to reduce the emission of pollutants, when interpreted within the context of the exercise intensity domain schema, their associated exertional intensity is likely insufficient to confidently elicit cardiorespiratory benefits.

The acquisition of a motor skill involves adaptations of spinal and supraspinal pathways to alpha motoneurons. In this study, we estimated the shared synaptic contributions of these pathways to understand the neural mechanisms underlying the short-term acquisition of a new force-matching task. High-density surface electromyography (HDsEMG) was acquired from the first dorsal interosseous (FDI; 7 males and 6 females) and tibialis anterior (TA; 7 males and 4 females) during 15 trials of an isometric force-matching task. For two selected trials ( pre- and post-skill acquisition), we decomposed the HDsEMG into motor unit spike trains, tracked motor units between trials, and calculated the mean discharge rate and the coefficient of variation of inter-spike interval (CoV _ISI ). We also quantified the post/pre ratio of motor units’ coherence within delta, alpha, and beta bands. Improvements in force-matching were accompanied by a significant increase in the mean discharge rate and a decrease in CoV _ISI for both muscles. Moreover, the area under the curve within alpha band decreased by ∼22% and ∼13% for the TA and FDI muscles, respectively, with no changes in the delta or beta bands. These reductions correlated significantly with increased coupling between force/neural drive and target oscillations. These results suggest that the short-term acquisition of a new force-matching skill is mediated by the attenuation of tremor oscillations in the shared synaptic inputs. In other words, the central nervous system acts as a matched filter to modulate the synaptic weights of shared inputs and suppress neural components unrelated to the specific task. Supported by simulations, a plausible mechanism behind these alpha band reductions may involve spinal interneurons’ phase-cancelling descending oscillations.

Background: While promoting active mobility and outdoor activities can benefit health (HLT), it also increases Exposure (EXP) to air pollutants, such as particulate matter (PM), due to the increased ventilation rate (VR) under physical activity. Traditional assessments of individual (IND) PM EXP involve costly equipment inaccessible to the public, but real-time low-cost sensors (LCS) are now emerging. This study presents a proof of concept to demonstrate the use of LCS for examining the real-time IND respiratory dose deposited (RDD) to PM cycling across the Brescia province. Methods: An e-bike was ridden 33 times between 2022 and 2023 wearing a LCS for PM concentration [PM] linked to a GPS. Respiratory dose deposited(RDD) was calculated for six different locations within each route based on experimental PM and various VR. Results: The LCS allows for the study of the spatial and temporal variability of [PM], revealing a significant difference (p < 0.01) according to the heating system operation and no significant difference (p > 0.05) depending on the location. RDD increases with [PM] and VR. Real-time and integrated RDD is calculated for routes with high (> 50 µg/m3), medium (25 µg/m3), and low (<10 µg/m3) [PM2.5]. The e-bike assistance is activated when the WHO interim target 4 of [PM] is reached to reduce VR, which corresponds to a shift to a lower physical activity intensity. The RDD calculated using the e-bike assistance over the path reduces RDD by about 23% and 11% over the high and medium [PM], while it never activates for the low [PM]. Conclusions: This study demonstrates that the use of LCS allows the estimation of IND RDD, and the implementation of mitigation strategies based on controlled assistance from e-bikes would enable the reduction of PM individual EXP. Key messages: • The integration of HLT data from wearable and air quality LCS enables the promotion of active mobility and outdoor activities controlling the EXP to air pollutants. • Establishing generalized guidelines based on this mitigation strategies for individual exposure reduction may also inform policy recommendations for promoting active and green mobility.