Studying the Changes in Physical Functioning and Oxidative Stress-Related Molecules in People Living with HIV after Switching from Triple to Dual Therapy

BACKGROUND

Physical activity could increase the production of oxidative stress biomarkers, affecting the metabolism and excretion of antiretroviral drugs and, consequently, the clinical outcome. Nowadays, people living with HIV (PLWH) are mostly switching from triple to dual therapy, but no data are available in terms of physical functioning and oxidative stress. The aim of this study was to evaluate if some antioxidant biomarkers and physical functioning tests could be different according to triple or dual antiretroviral therapy.

METHODS

PLWH were evaluated at baseline (BL), while treated with three drugs, and six months after the switch to dual therapy. Physical functioning was quantified using validated tools. Mitochondrial and cytosol antioxidant molecules were evaluated through liquid chromatography.

RESULTS

Twenty-five patients were analyzed. A statistically significant difference between triple and dual therapy was found for mitochondrial glutathione, but not for physical tests. Evaluating differences between physically active and inactive individuals, the following statistically significant differences were suggested, considering triple therapy (mitochondrial n-formyl-methionine p = 0.022, triglycerides p = 0.023) and double therapy (mitochondrial glycine p = 0.035, cytosol glutamic acid p = 0.007, cytosol s-adenosylmethionine p = 0.021).

CONCLUSIONS

For the first time, this study suggests possible differences in terms of antioxidant molecules and physical functioning in PLWH switching from triple to dual therapy.

Decreased neural drive affects the early rate of force development after repeated burst-like isometric contractions

The neural drive to the muscle is the primary determinant of the rate of force development (RFD) in the first 50 ms of a rapid contraction. It is still unproven if repetitive rapid contractions specifically impair the net neural drive to the muscles. To isolate the fatiguing effect of contraction rapidity, 17 male adult volunteers performed 100 burst-like (i.e., brief force pulses) isometric contractions of the knee extensors. The response to electrically-evoked single and octet femoral nerve stimulation was measured with high-density surface electromyography (HD-sEMG) from the vastus lateralis and medialis muscles. Root mean square (RMS) of each channel of HD-sEMG was normalized to the corresponding M-wave peak-to-peak amplitude, while muscle fiber conduction velocity (MFCV) was normalized to M-wave conduction velocity to compensate for changes in sarcolemma properties. Voluntary RFD 0-50 ms decreased (d = -0.56, p < 0.001) while time to peak force (d = 0.90, p < 0.001) and time to RFDpeak increased (d = 0.56, p = 0.034). Relative RMS (d = -1.10, p = 0.006) and MFCV (d = -0.53, p = 0.007) also decreased in the first 50 ms of voluntary contractions. Evoked octet RFD 0-50 ms (d = 0.60, p = 0.020), M-wave amplitude (d = 0.77, p = 0.009) and conduction velocity (d = 1.75, p < 0.001) all increased. Neural efficacy, i.e., voluntary/octet force ratio, largely decreased (d = -1.50, p < 0.001). We isolated the fatiguing impact of contraction rapidity and found that the decrement in RFD, particularly when calculated in the first 50 ms of muscle contraction, can mainly be explained by a decrease in the net neural drive.

Impact of active lifestyle on the primary school children saliva microbiota composition

The aim of the study was to evaluate the effects of Active or Sedentary lifestyle on saliva microbiota composition in Italian schoolchildren.

Methods

Male (114) and female children (8-10 years) belonging to five primary schools in the neighborhoods of Turin were classified as active (A) or sedentary (S) based on PAQ-C-It questionnaire. PCR amplification of salivary DNA targeted the hypervariable V3-V4 regions of the 16S rRNA bacterial genes. DADA2 workflow was used to infer the Amplicon Sequence Variants and the taxonomic assignments; the beta-diversity was obtained by PCoA with the UniFrac method; LEfSe algorithm, threshold at 5%, and Log LDA cutoff at ±0.5 were used to identify differently abundant species in A compared to S saliva sample. Daily food intake was assessed by 3-Days food record. The metabolic potential of microbial communities was assessed by PICRUSt.

Results

No significant differences were found in individual's gender distribution (p = 0.411), anthropometry, BMI (p > 0.05), and all diet composition between A and S groups (p > 0.05). Eight species were differently abundant: Prevotella nigrescens (LDA score = -3.76; FDR = 1.5×10-03), Collinsella aerofaciens (LDA score = -3.17; FDR = 7.45×10-03), Simonsiella muelleri (LDA score = -2.96; FDR = 2.76×10-05), Parabacteroides merdae (LDA score = -2.43; FDR = 1.3×10-02) are enriched in the A group; Gemella parahaemolysans, Prevotella aurantiaca (LDA score = -3.9; FDR = 5.27×10-04), Prevotella pallens (LDA score = 4.23; FDR = 1.93×10-02), Neisseria mucosa (LDA score = 4.43; FDR = 1.31×10-02; LDA score = 2.94; FDR = 7.45×10-03) are enriched in the S group. A prevalence of superpathway of fatty acid biosynthesis initiation (E. coli) and catechol degradation II (meta-cleavage pathway) was found in saliva from A compared to S children.

Conclusion

Our results showed that active children had an enrichment of species and genera mainly associated with a healthier profile. By contrast, the genera and the species enriched in the sedentary group could be linked to human diseases.

Two Is Better than One: Successful World-Class Sprinters Compete in Two Disciplines

We aimed to quantify the prevalence of track and field sprinters competing at a world-class level in more than one discipline, and we describe the career characteristics of single- and double-discipline athletes in terms of peak performance and the age of peak performance. The career performance of athletes ranked in the top 200 positions of the World Athletics database in the 100 m, 200 m, and 400 m were analyzed, i.e., 5514 career profiles (49.9% female). Using binomial proportion, we calculated how many competed in only one or more than one discipline. We also compared the peak performance and the age of peak performance of athletes who competed in one vs. more than one discipline. Independent of gender, about 50% of the athletes competing in the 100 m and 200 m also competed in the other discipline (i.e., 200 m and 100 m, respectively). Differently, only 20% of the athletes competing in the 400 m also competed in the 200 m. Sprinters competing in the 100-200 m and 200-400 m couples showed better peak performance than the sprinters competing in only one discipline. Many world-class sprinters compete in two disciplines, and the 100-200 m was the most prevalent couple. Our results also suggest that sprinters who compete in two disciplines may be advantaged compared to sprinters who compete in only one event.

Neural and contractile determinants of burst-like explosive isometric contractions of the knee extensors

Walking and running are based on rapid burst-like muscle contractions. Burst-like contractions generate a Gaussian-shaped force profile, in which neuromuscular determinants have never been assessed. We investigated the neural and contractile determinants of the rate of force development (RFD) in burst-like isometric knee extensions. Together with maximal voluntary force (MVF), voluntary and electrically evoked (8 stimuli at 300 Hz, octets) forces were measured in the first 50, 100, and 150 ms of burst-like quadriceps contractions in 24 adults. High-density surface electromyography (HDsEMG) was adopted to measure the root mean square (RMS) and muscle fiber conduction velocity (MFCV) from the vastus lateralis and medialis. The determinants of voluntary force at 50, 100, and 150 ms were assessed by stepwise multiple regression analysis. Force at 50 ms was explained by RMS (R²  = 0.361); force at 100 ms was explained by octet (R²  = 0.646); force at 150 ms was explained by MVF (R²  = 0.711) and octet (R²  = 0.061). Peak RFD (which occurred at 60 ± 10 ms from contraction onset) was explained by MVF (R²  = 0.518) and by RMS₅₀ (R²  = 0.074). MFCV did not emerge as a determinant of RFD. Muscle excitation was the sole determinant of early RFD (50 ms), while contractile characteristics were more relevant for late RFD (≥100 ms). As peak RFD is mostly determined by MVF, it may not be more informative than MVF itself. Therefore, a time-locked analysis of RFD provides more insights into the neuromuscular characteristics of explosive contractions.

"Stay at Home" during the COVID-19 Pandemic: Effects on Physical Activity and Sedentary Behavior in an Italian Academic Community

This study investigates changes in physical activity (PA) and sedentary behavior in an Italian university community during Phase 1 of SARS-CoV-2 lockdown (“stay at home” government decree, from March 8th to May 4th, 2020) compared to their habits prior to the COVID-19 pandemic. We also examine differences according to gender, university position, BMI categories, and sport participation. A total of 2596 people (median age 24, IQR 11 years; 70.8% women) filled out a survey after eight weeks of statutory confinement at home. The International Physical Activity Questionnaire measured PA and sedentary behavior in a typical week before and during lockdown. Physically inactive people passed from 10.9% to 35.0% before−during the lockdown. The total amount of PA decreased (median 2307 vs. 1367 MET-min/week; p < 0.001), while sedentary behavior increased (median 349 vs. 440 min/day; p < 0.001) between before and during the lockdown. The following categories showed a higher reduction in the total amount of PA: men when compared to women; people with normal weight when compared to pre-obese/obese people; and people who played sports when compared to those who did not play sports. There is a need to propose PA/exercise programs to counteract physical inactivity and sedentarism during a social emergency, with special attention to people who showed higher PA reduction.

Optimal bipolar system positioning to provide information about the trapezius activity associated with scapular retraction during shoulder exercises for resistance training

Objective. Recently, the use of EMG biofeedback to make subjects aware of the stabilizer activation associated with scapular retraction during exercise has been of interest, and challenges related to EMG detection have been addressed. Whether there is an optimal bipolar positioning that discriminates the stabilizer activation with retraction from a neutral scapular position during resistance exercises is an open issue that we address here by simultaneously mapping different positions using high-density surface electromyography (HD-sEMG).Approach. Sixteen resistance-trained males performed five pulling exercises with and without scapular retraction, namely barbell rows, dumbbell rows, pull-downs at a lat machine, seated rows, and TRX (total resistance exercises) system rows. HD-sEMG was acquired in a monopolar mode from the medial and lower trapezius (8 × 4 electrodes and inter-electrode distance (ied): 10 mm) and different bipolar systems were simulated in terms of positioning, interelectrode distance, and orientation with respect to the spine: longitudinal with three ieds (20 mm, 30 mm, and 40 mm), one transversal, and two diagonals (ied: 20 mm), totalling six EMG sets. To identify the optimal electrode pair that was able to distinguish between the presence or absence of scapular retraction, we computed: (i) the root mean square (RMS) map for each condition and the difference between them, obtaining a differential RMS map per subject; and (ii) the intersection of cumulative maps, by summing the differential (binary) maps from all subjects.Main results. For the lower trapezius, the results revealed that the diagonal direction (45 degrees; ied: 20 mm) obtained the greater occurrence of intersecting segments within and between exercises than the other electrode configurations, showing low variability for the optimal positioning across exercises. Electrode configuration varied within and between the pulling exercises for the medial trapezius.Significance. This study allows us to identify an optimal bipolar positioning (consistent across subjects and exercises) for lower trapezius activity assessment, representing a guideline for electrode positioning when EMG biofeedback is adopted for selective activation of the lower trapezius during pulling exercises.

Indoor Mobility, Frailty, and Disability in Community-Dwelling Older Adults: A Mediation Model

The general population, but especially older adults, were forced or encouraged to stay home during the recent COVID-19 pandemic. In this context, indoor mobility (IM, the number of steps performed daily at home) may be informative about the general health status of older adults. The present study aimed at evaluating the relationship between IM, frailty (loss of functional reserve including both physical and psychosocial domains), and disability (loss of autonomy measured as activities of daily life, ADLs) in a sample of community-dwelling Italian older adults. Specifically, the primary objective was to investigate IM and disability differences between robust and frail older adults. The secondary objective was to test if frailty is in the causal sequence between IM and disability, i.e., as a mediator in their relationship. Thirty-two participants (mean age = 70 ± 6 years; 56.2% women) were recruited. Frailty and disability were evaluated using the Tilburg Frailty Indicator and the Groningen Activity Restriction Scale, respectively. IM at home was measured via an Adamo wristwatch (a connected accelerometer). One-way analyses of covariance, controlling for age and gender, showed that robust participants, classified according to a score higher than five points in the Tilburg Frailty Indicator, performed significantly more IM (F_1,28 = 4.639; p = 0.04) and presented lower disability grade than frail ones (F_1,28 = 4.342; p =0.046). Only physical frailty was a mediator in the relationship between IM and disability (F_2,29 = 8.538, p < 0.001), with a fully mediated model (z = -2.073, p < 0.04). Conversely, the total frailty score was not a mediator in the same relationship, but with IM accounted for the variance in disability (F_2,29 = 8.538, p < 0.001; R² = 33.7%). Our results suggested that frail older adults restricted their IM more and presented a higher level of disability compared to robust older adults. Moreover, data suggest that IM reduction may have a negative impact on physical frailty and indirectly increase disability.

Strength Asymmetries Are Muscle-Specific and Metric-Dependent

We investigated if dominance affected upper limbs muscle function, and we calculated the level of agreement in asymmetry direction across various muscle-function metrics of two heterologous muscle groups. We recorded elbow flexors and extensors isometric strength of the dominant and non-dominant limb of 55 healthy adults. Participants performed a series of explosive contractions of maximal and submaximal amplitudes to record three metrics of muscle performance: maximal voluntary force (MVF), rate of force development (RFDpeak), and RFD-Scaling Factor (RFD-SF). At the population level, the MVF was the only muscle function that showed a difference between the dominant and non-dominant sides, being on average slightly (3–6%) higher on the non-dominant side. At the individual level, the direction agreement among heterologous muscles was poor for all metrics (Kappa values ≤ 0.15). When considering the homologous muscles, the direction agreement was moderate between MVF and RFDpeak (Kappa = 0.37) and low between MVF and RFD-SF (Kappa = 0.01). The asymmetries are muscle-specific and rarely favour the same side across different muscle-performance metrics. At the individual level, no one side is more performative than the other: each limb is favoured depending on muscle group and performance metric. The present findings can be used by practitioners that want to decrease the asymmetry levels as they should prescribe specific exercise training for each muscle.

Effects of a Multicomponent Exercise Program on Prevalence and Severity of the Frailty Syndrome in a Sample of Italian Community-Dwelling Older Adults

Background: Frailty is a well-known condition that leads to a lack of resilience, with a reduced homeostatic capacity and a consequent higher risk of suffering adverse health outcomes. This study investigated the effectiveness of an exercise program to improve and reverse physical frailty amongst Italian older adults. Methods: One hundred and twenty-three community dwelling older adults (mean age 74 years, SD = 6; 64% women) were involved in an experimental (EG; n = 62) and a control (CG; n = 61) group. Frailty was assessed at baseline and after the intervention using an adapted version of the frailty phenotype. The EG took part in a 16-week exercise program, consisting of endurance, strength, balance and flexibility exercises, while the CG maintained the same routine. Results: After the exercise program, the EG was more robust than the CG (F = 43.51, p < 0.001). Within the EG, 46% of pre-frail and 50% of frail people reached the robust and pre-frail levels, respectively. Effects of training were higher in frail and pre-frail people (reduction of frailty of 0.67 and 0.76 points, respectively) compared to robust ones (who frailty levels increased by 0.23 points; F = 11.32, p < 0.001). Conclusions: A multicomponent exercise program may be effective at improving and reverting frailty, specifically for frail and pre-frail people.

The Cut-Off Value for Classifying Active Italian Children Using the Corresponding National Version of the Physical Activity Questionnaire

The present study aimed to determine a cut-off value following the filling in of a questionnaire (PAQ-C-It) to identify active Italian children. One-hundred-twenty-nine primary school children (5 Piedmont schools; 47.3% female; mean age = 10 ± 1 years) wore an accelerometer (Actigraph wGT3X-BT) to objectively quantify individual moderate-to-vigorous physical activity during one week. Afterwards, the PAQ-C-It was filled in by participants. A ROC curve procedure was applied to obtain an active/non-active cut-off point. Spearman’s correlation coefficient was also applied to establish the relationship between the two parameters. According to the ROC analysis, the PAQ-C-It cut-off point value is identifiable at >2.75 to indicate active children (area under the curve = 0.62; standard error = 0.05; p = 0.025; coefficient intervals = 0.518−0.716; sensitivity = 0.592, specificity = 0.382), determining that 65 participants (55%) were non-active (mean PAQ-C-It value = 2.3 ± 0.4; active mean PAQ-C-It value = 3.3 ± 0.4). Spearman’s correlation coefficient results were significant but with a small effect size (rho = 0.214; p = 0.008). In conclusion, the present results suggest that the PAQ-C-It can be cautiously used as tool to practically classify active Italian children because of a non-solid relationship between respective accelerometer data and MVPA daily data.

Rate of Force Development as an Indicator of Neuromuscular Fatigue: A Scoping Review

Because rate of force development (RFD) is an emerging outcome measure for the assessment of neuromuscular function in unfatigued conditions, and it represents a valid alternative/complement to the classical evaluation of pure maximal strength, this scoping review aimed to map the available evidence regarding RFD as an indicator of neuromuscular fatigue. Thus, following a general overview of the main studies published on this topic, we arbitrarily compared the amount of neuromuscular fatigue between the “gold standard” measure (maximal voluntary force, MVF) and peak, early (≤100 ms) and late (>100 ms) RFD. Seventy full-text articles were included in the review. The most-common fatiguing exercises were resistance exercises (37% of the studies), endurance exercises/locomotor activities (23%), isokinetic contractions (17%), and simulated/real sport situations (13%). The most widely tested tasks were knee extension (60%) and plantar flexion (10%). The reason (i.e., rationale) for evaluating RFD was lacking in 36% of the studies. On average, the amount of fatigue for MVF (−19%) was comparable to late RFD (−19%) but lower compared to both peak RFD (−25%) and early RFD (−23%). Even if the rationale for evaluating RFD in the fatigued state was often lacking and the specificity between test task and fatiguing exercise characteristics was not always respected in the included studies, RFD seems to be a valid indicator of neuromuscular fatigue. Based on our arbitrary analyses, peak RFD and early phase RFD appear even to be more sensitive to quantify neuromuscular fatigue than MVF and late phase RFD.

Is fatigue a muscular phenomenon in Parkinson's disease? Implications for rehabilitation

BACKGROUND

Fatigue in Parkinson's Disease (PD) compromises patients' physical activity and poses questions on how to plan correct rehabilitation training. In addition, the relationship between subjective perceived fatigue and fatigue in motor performance is not yet entirely understood. As a consequence, a conclusive interpretation of muscular mechanisms of fatigue in PD has not yet been achieved. Among the various instrumental evaluations for fatigue, multichannel surface electromyography (sEMG) is a recognized tool that permits the study of myoelectric manifestations of fatigue.

AIM

To assess if muscles in PD show a different myoelectric fatigue pattern compared to the muscles of healthy age-matched subjects.

DESIGN

Observational controlled study.

POPULATION

Idiopathic Parkinson's Disease, Hohen &Yahr II and III stage, Parkinsonian Fatigue Scale average score ≥ 2.95, no therapy modification in the 4 weeks preceding the study; exclusion criteria: Mini Mental State Examination ≤ 24, upper limb disease/symptoms that might interfere with sEMG analysis, presence of other fatiguerelated conditions. Twenty patients were selected according to these criteria. Twenty untrained healthy subjects were matched.

METHODS

All subjects underwent a muscle fatigue protocol and a sEMG analysis of the right biceps brachii muscle during electrically stimulated and voluntary contractions in order to obtain a myoelectric fatigue muscular pattern. The myoelectric pattern is characterized by the modifications of the following sEMG variables: reduction of mean frequency and muscle fibre conduction velocity, increase of average rectified value.

RESULTS

No statistical differences where observed between groups for sEMG variables and muscular electric behaviour in all contraction conditions (all p> .05).

CONCLUSIONS

Our results show that parkinsonian muscles does not differ from the muscles of healthy age-matched subjects in developing peripheral myoelectric fatigue. Nevertheless, the role of fatigue perception at rest and particularly during physical activity must be clearly understood in order to further target the rehabilitative approach for fatigued parkinsonian patients and to reduce hypomobility.

CLINICAL REHABILITATION IMPACT

In rehabilitative terms, these findings allow us to highlight the possibility of performing sustained training with isometric contractions in PD subjects; therefore, fatigue "per se" does not constitute a barrier for the execution of muscular exercises, likewise intensive.

Relation among Perceived Weight Change, Sedentary Activities and Sleep Quality during COVID-19 Lockdown: A Study in an Academic Community in Northern Italy

In Italy, COVID-19 lockdown was imposed from 8 March until 3 May 2020 with negative consequences on the lifestyles and health of people. Within this context, the paper aims: (i) to analyse the impact of COVID-19 lockdown on perceived weight changes; (ii) to evaluate factors associated with the perception of weight changes (Body Mass Index (BMI), sleep quality, time spent in sedentary activities), in an Italian academic community of students and workers. A total of 3666 participants took part in this cross-sectional study (2838 students and 828 workers, of whom 73.0% were female). T-test, Chi-square test and the two-way ANOVA were used. Results showed that 43.3% of participants perceived a weight gain. Workers experienced a more substantial increase in body weight (0.7 kg) compared to students (0.3 kg; p = 0.013). A significant difference between preobese/obese workers (0.9 kg) and students (-0.3 kg; p < 0.001) was found. Overall, 57.0% of the sample was characterized by high levels of sedentary activities. Sedentary people noticed a higher weight gain (0.4 kg) compared to less sedentary people (0.3 kg; p = 0.048). More than 45% of participants reported a worsening of sleep quality and showed a perceived increase in body weight (0.5 kg) in comparison to those who improved their sleep quality (no weight change; p = 0.001). Designing tailored interventions to promote health-related behaviours during lockdown periods is essential.

ADAMO INDOOR MOBILITY, PHYSICAL FRAILTY, AND AUTONOMY IN OLDER ADULTS: A MEDIATION MODEL

Physical frailty represents a clinical condition among older adults leading to adverse health outcomes, such as autonomy loss. To evaluate physical frailty in older adults, adopting information and communication technologies (ICT) may be useful. ADAMO (Caretek S.r.l.) is a care-watch accelerometer that allows to measure mobility in a non-intrusive way (Magistro et al., 2018) providing wider information on individual general health (Mulasso et al., in press). The aim of this study was to evaluate the relationship between indoor mobility, physical frailty and autonomy in a sample of Italian older adults. Methods: Thirty-two volunteers (age 65–84 years; women 56.2%) participated in the study. All wore ADAMO care-watch continuously over a 7-day period. The number of steps indoor was the main endpoint. Fragmented daily mobility was estimated. Physical frailty and autonomy were measured using the Tilburg Frailty Indicator (physical components) and the Groningen Activity Restriction Scale, respectively. Results: Significant inverse correlations were observed between number of steps and autonomy, and number of steps and physical frailty. Conversely, a significant direct correlation was observed between physical frailty and autonomy. Additionally, mediation analysis demonstrated full mediation effect of physical frailty between the number of steps and autonomy. Our results imply that high indoor mobility per se can reduce physical frailty and consequently helps to maintain autonomy. Conclusions: Indoor mobility captured by ADAMO accelerometer may be an important indicator of physical frailty and autonomy. ADAMO may be used as a non-intrusive telemonitoring solution to capture relevant information on individual general health in aged people.

LONG-TERM GAIT SPEED TELEMONITORING IN OLDER ADULTS WITH MILD COGNITIVE IMPAIRMENT OR MILD DEMENTIA. THE DECI STUDY

Non-intrusive telemonitoring of physical activity in Older Adults suffering from Mild Cognitive Impairment (MCI), or Mild Dementia (MD), was implemented as part of a 6-month multicomponent digital intervention in the DECI study (EU Horizon2020 grant No 643588). Methods: To estimate gait speed long-term trajectory, a processing algorithm was applied on individual accelerometry data continuously recorded via the ADAMO wrist-watch accelerometer. Speed Trend Analysis was performed if patients wore the device ≥90 days. Only outdoor activity was analyzed to reflect patients’ own natural gait speed. Only time spent in high or very-high-activity level is used, to eliminate rest periods (e.g. sitting on a bench, on a bus or driving). A raw mean walking speed was computed. Stride was computed from gender and height and walked distance from stride and step count. Mean walking speed was estimated by walking distance and duration. A rolling mean algorithm was applied to the computed mean 15-day baseline series, resulting in a new series representing normalized patient’s gait speed trajectory during the study. Results: Baseline characteristics: F/M=21/19; MCI/MD=36/4; age=75.4±6.0 years; BMI= 24.6±5,2; MMSE=26.5±2.4; education=8.9±4.0 years. Monitoring days=147±29. Overall three main patterns of gait speed trajectory were identified: “relative stability”, “improving trend” and “progressive decline”: No evident correlation with cognitive status was observed in the sample. Examples of individual patterns are shown. Conclusions: Gait Speed Analysis can describe physical function trajectory over time and identify decliners from stable or improving older adults. Further analyses may clarify the relationship between physical function changes and cognitive status.

The Daily Mile: 15 Minutes Running Improves the Physical Fitness of Italian Primary School Children

The Daily Mile™ is an innovative school-based intervention that requires children to run or jog outside for 15 min at a self-selected pace during class time. Today, only one study has investigated the efficacy of The Daily Mile on physical fitness, which was conducted with Scottish children. Thus, we aimed to evaluate the feasibility and effectiveness of The Daily Mile in Italian primary schools. A total of 486 children participated in The Daily Mile for 3 months (experimental group), whereas 309 children continued their daily school routine (control group). The 6-min run test, standing long jump, body mass index, and waist-to-height ratio were assessed. Their teachers completed surveys for assessing the intervention acceptability. After correction for age and gender, significant group × time interactions were observed in the 6-min run test and standing long jump results. In the post-test period, the experimental group showed improvement in the 6-min run test and standing long jump results. Overall, the teachers were satisfied with the program and found it suitable for their school context and easy to implement. The Daily Mile was successfully implemented and smoothly accepted in the day routine of Italian primary schools.

Motor unit discharge rate and the estimated synaptic input to the vasti muscles is higher in open compared with closed kinetic chain exercise

Conflicting results have been reported on whether closed kinetic chain exercises (such as a leg press) may induce more balanced activation of vastus medialis (VM) and lateralis (VL) muscles compared with open kinetic chain exercise (such as pure knee extension). This study aimed to 1) compare between-vasti motor unit activity and 2) analyze the combined motor unit behavior from both muscles between open and closed kinetic chain exercises. Thirteen participants (four women, mean ± SD age: 27 ± 5 yr) performed isometric knee extension and leg press at 10, 30, 50, 70% of the maximum voluntary torque. High density surface EMG signals were recorded from the VM and VL and motor unit firings were automatically identified by convolutive blind source separation. We estimated the total synaptic input received by the two muscles by analyzing the difference in discharge rate from recruitment to target torque for motor units matched by recruitment threshold. When controlling for recruitment threshold and discharge rate at recruitment, the motor unit discharge rates were higher for knee extension compared with the leg press exercise at 50% [estimate = 1.2 pulses per second (pps), standard error (SE) = 0.3 pps, P = 0.0138] and 70% (estimate = 2.0 pps, SE = 0.3 pps, P = 0.0001) of maximal torque. However, no difference between the vasti muscles were detected in both exercises. The estimates of synaptic input to the muscles confirmed these results. In conclusion, the estimated synaptic input received by VM and VL was similar within and across exercises. However, both muscles had higher firing rates and estimated synaptic input at the highest torque levels during knee extension. Taken together, the results show that knee-extension is more suitable than leg-press exercise at increasing the concurrent activation of the vasti muscles.

NEW & NOTEWORTHY There is a significant debate on whether open kinetic chain, single-joint knee extension exercise can influence the individual and combined activity of the vasti muscles compared with closed kinetic chain, multijoint leg press exercise. Here we show that attempting to change the contribution of either the vastus medialis or vastus lateralis via different forms of exercise does not seem to be a viable strategy. However, the adoption of open kinetic chain knee extension induces greater discharge rate and estimated synaptic input to both vasti muscles compared with the leg press.

Relative Age Influences Performance of World-Class Track and Field Athletes Even in the Adulthood

The relative age effect (RAE) is a common phenomenon observed in youth sports and is characterized by a significant over-representation of athletes born close to the date of selection. However, there is a lack of research on RAE in world-class track and field athletes and it is not clear if this effect persists into adulthood. Thus, this study examined for the first time the prevalence and magnitude of RAE at world class level in all track and field disciplines. Birthdates of 39,590 athletes (51.6% females) ranked in the International Association of Athletics Federations top 100 official lists between 2007 and 2018 season of Under 18, Under 20, and Senior categories were collected. Under 18 and Under 20 athletes born in the first week of the year are about 2 to 3.5 times more likely to be included in the top-100 ranking than the athletes born in the last week of the year. RAE was overall larger in male compared to female athletes. In some disciplines (e.g., throwing events) RAE persists in Senior category. These findings suggest that in some disciplines relatively younger athletes may have less chances of reaching world-class performances even in the adulthood. Governing bodies should reflect upon their policies for athlete support and selection to minimize the RAE.

A comparison between an ICT tool and a traditional physical measure for frailty evaluation in older adults

Background

Frailty is a clinical condition among older adults defined as the loss of resources in one or more domains (i.e., physical, psychological and social domains) of individual functioning. In frail subjects emergency situations and mobility levels need to be carefully monitored. This study aimed to: i) evaluate differences in the mobility index (MI) provided by ADAMO system, an innovative remote monitoring device for older adults; ii) compare the association of the MI and a traditional physical measure with frailty.

Methods

Twenty-five community-dwelling older adults (71 ± 6 years; 60% women) wore ADAMO continuously for a week. The time percentage spent in Low, Moderate and Vigorous Activities was assessed using ADAMO system. Walking ability and frailty were measured using the 400 m walk test and the Tilburg Frailty Indicator, respectively.

Results

Controlling for age and gender, the ANCOVA showed that frail and robust participants were different for Low (frail = 58.8%, robust = 42.0%, p < 0.001), Moderate (frail = 25.5%, robust = 33.8%, p = 0.008), and Vigorous Activity (frail = 15.7%, robust = 24.2%, p = 0.035). Using cluster analysis, participants were divided into two groups, one with higher and one with lower mobility. Controlling for age and gender, linear regression showed that the MI clusters were associated with total (β = 0.571, p = 0.002), physical (β = 0.381, p = 0.031) and social (β = 0.652, p < 0.001) frailty; and the 400 m walk test was just associated with total (β = 0.404, p = 0.043) and physical frailty (β = 0.668, p = 0.002).

Conclusion

ADAMO system seems to be a suitable time tracking that allows to measure mobility levels in a non-intrusive way providing wider information on individual health status and specifically on frailty. For the frail individuals with an important loss of resources in physical domain, this innovative device may represent a considerable help in preventing physical consequences and in monitoring functional status.

Relevance of evaluating the rate of torque development in ballistic contractions of submaximal amplitude

OBJECTIVE

The neuromuscular quickness capacity can be assessed by calculating the rate of torque development (RTD) during ballistic contractions of maximal (RTD_maximal) or submaximal (RTD_submaximal) amplitudes. In a series of ballistic contractions of submaximal amplitudes, the RTD scaling factor (RTD-SF) represents the slope of the linear regression between achieved peak torques and the corresponding RTD. First we investigated whether the RTD-SF contributes to the prediction, together with maximal voluntary torques (MVT), of the RTD_maximal. Then, we evaluated the agreement between the z-scores of RTD_maximal and RTD_submaximal.

APPROACH

The MVT was obtained for the quadriceps and hamstrings muscles of 22 elite young soccer players. RTD-SF was quantified in a series of ballistic contractions of submaximal and maximal amplitudes. RTD_submaximal was estimated from the regression relationship between the peak torques and the corresponding RTD.

MAIN RESULTS

MVT, RTD-SF and y -intercept in total accounted for 76.9 and 61.2% of the variance in RTD_maximal in quadriceps and hamstrings, respectively. Specifically, RTD-SF accounted for 13.7% and 18.7% of the variance in RTD_maximal, respectively. Generally, the agreement between the z-scores of RTD_maximal and RTD_submaximal was poor both in quadriceps and hamstrings.

SIGNIFICANCE

These results suggest that RTD-SF may have a functional relevance in the relationship between MVT and RTD_maximal and influence the amount of torque that can be achieved in a quick muscle contraction. Moreover, evaluating the RTD_submaximal does not provide results that are interchangeable with RTD_maximal. Thus, evaluating the RTD across the whole range of torque could provide additional meaningful information about neuromuscular quickness.

Neuromuscular efficiency in fibromyalgia is improved by hyperbaric oxygen therapy: looking inside muscles by means of surface electromyography

OBJECTIVES

Neuromuscular efficiency (NME) is impaired in fibromyalgia (FM). Hyperbaric oxygen therapy (HBOT) is a medical treatment using 100% of oxygen through an oxygen mask. HBOT in FM induces changes in cortical excitability and a secondary reduction in pain and muscle fatigue. However, there are still no direct data indicating changes in muscle fatigue. The aim of this study was to assess whether the reduction in muscle fatigue so far attributed to a central effect of HBOT can be directly detected by means of non-invasive sEMG as a change in NME.

METHODS

The study was an observational longitudinal study on changes in NME induced by 20 sessions of HBOT at 2.4 atmosphere, in 22 patients with FM (3M; 19F) (age 49.8±9.5; height 164.7±7.5; weight 63.8±12.7). sEMG was recorded in single differential configuration from the biceps brachii muscle during the 30-second fatiguing contractions using linear arrays of eight adhesive electrodes.

RESULTS

Evaluations made before and immediately after the first session showed that maximal strength did not change (T0 49±20 N, T1 49±19 N, p=0.792), thus suggesting that HBOT did not induce muscle fatigue or potentiation. After 20 sessions of HBOT, NME increased from 1.6±1.1 to 2.1±0.8 (p=0.050), whereas maximal strength, EMG amplitude and muscle fibre CV did not change.

CONCLUSIONS

HBOT did not improve muscle strength or change muscle fibre content, but improved the ability of the central motor command to generate the same effort (MVC) with fewer recruited fibres. Our sEMG findings underlined a modified central mechanism related to fibre type recruitment order, thus suggesting that muscle fatigue is not primarily a muscular problem, as also demonstrated by other authors with different methods.

Interlimb Asymmetries Identified Using the Rate of Torque Development in Ballistic Contraction Targeting Submaximal Torques

Evaluating the rate of torque development (RTD) in isometric ballistic contraction targeting submaximal torques is usually overlooked in the literature. In a series of isometric ballistic contractions targeting a range of submaximal torque values, there is a linear relationship between the peak torque and the peak RTD obtained in each contraction. RTD scaling factor (RTD-SF) represents the slope of this relationship. In this study, we investigated the prevalence of interlimb asymmetry in the RTD-SF and in the RTD calculated across submaximal torques. Furthermore, we compared these asymmetry indices with those calculated adopting more classical approaches, such as ballistic contraction targeting maximal torque and isokinetic concentric conditions. Quadriceps and hamstrings strength was evaluated in both limbs of elite under 17 and under 19 soccer players (20 males, 17 ± 1 years). Participants performed three concentric isokinetic contractions at 240°/s and a series of isometric ballistic contractions targeting from 20 to 100% of maximal isometric torque. The interlimb difference was calculated for each parameter and players presenting an interlimb difference >15% were identified. A total of 40% (for quadriceps) and 60% (for hamstring) of players showed an interlimb asymmetry in isometric RTD for at least 50% of submaximal torque range. The RTD-SF was able to identify more players with asymmetry than the classical isokinetic tests. However, isokinetic and isometric indices of asymmetry were in general poorly or not correlated with each other. Most players presented an interlimb asymmetry in RTD for a wide part of the torque range and the adopted protocol was able to highlight important interindividual differences. Furthermore, players showed a large prevalence of RTD-SF asymmetry in both quadriceps and hamstrings. It is still to be determined if these asymmetries are functionally relevant. Nevertheless, the adopted protocol provided meaningful information for identifying interlimb asymmetries that could not be gathered when adopting the classical method of ballistic contractions targeting only maximal torques.

Neuromuscular Fatigue Does Not Impair the Rate of Force Development in Ballistic Contractions of Submaximal Amplitudes

The effect of muscle fatigue on rate of force development (RFD) is usually assessed during tasks that require participants to reach as quickly as possible maximal or near-maximal force. However, endurance sports require athletes to quickly produce force of submaximal, rather than maximal, amplitudes. Thus, this study investigated the effect of muscle fatigue induced by long-distance running on the capacity to quickly produce submaximal levels of force. Twenty-one male amateur runners were evaluated before and shortly after a half-marathon race. Knee extensors force was recorded under maximal voluntary and electrically evoked contractions. Moreover, a series of ballistic contractions at different submaximal amplitudes (from 20 to 100% of maximal voluntary force) was obtained, by asking the participants to reach submaximal forces as fast as possible. The RFD was calculated for each contraction. After the race, maximal voluntary activation, resting doublet twitch, maximal force, and RFD during maximal contraction decreased (-12, -12, -21, and -19%, respectively, all P-values < 0.0001). Nevertheless, the RFD values measured during ballistic contractions up to 60% of maximal force were unaffected (all P-values > 0.4). Long-distance running impaired the capacity to quickly produce force in ballistic contractions of maximal, but not of submaximal, amplitudes. Overall, these findings suggest that central and peripheral fatigue do not affect the quickness to which muscle contracts across a wide range of submaximal forces. This is a relevant finding for running and other daily life activities that rely on the production of rapid submaximal contractions rather than maximal force levels.

Participation in a school-based walking intervention changes the motivation to undertake physical activity in middle-school students

The motivation to perform physical activity is a crucial factor in achieving a persistent active lifestyle. However, motivation decreases with increasing age from childhood to adolescence. The promotion of physical activity in educational settings might be an important tool to increase motivation and, consequently, to decrease sedentary behavior. The aim of this study was to explore the effect of a 4-month school-based walking intervention on motivation to participate in physical activity among Italian middle-school students. This study included 276 students (mean age 13 ± 1 years, 41.3% female). A total of 138 students (intervention group) participated in a brief walking intervention that was added to their routine daily school activity, while a convenience sample of 138 students performed the routine daily school activity. The activity consisted of walking one kilometer outside of school buildings during the morning break. Motivation data were collected before and after the walking breaks using the Participation Motivation Questionnaire (PMQ). Controlling for age, significant interactions between group and time were observed in the "Social Status" [F(1,273) = 4.851; p = 0.028], "Team" [F(1,273) = 6.015; p = 0.015] and "Energy Release" components [F(1,273) = 8.527; p = 0.038]. Specifically, a significant decrease in the "Social Status" components of the PMQ and an increase in the "Team" and "Energy Release" components were observed in the intervention group. On the contrary. control group showed an increase in "Social Status" and a decrease in the "Team" and "Energy Release" components. Within this developmental context, incorporation of the walking activity helped to modify the motivational orientation towards physical activity to include more intrinsic factors, which were related to the possibility of remaining with classmates and peer groups and releasing a surplus of energy.

Elite national athletes reach their peak performance later than non-elite in sprints and throwing events

OBJECTIVES

The aim of this study was to describe and analyse the performance career trajectories for Italian athletes that participated in sprint, hurdles, discus throw, and shot-put athletics events.

DESIGN

Retrospective study, data collected between 1994 and 2014.

METHODS

A total of 5929 athletes (female: n=2977, 50.2%) were included in the study. The age of entering competition and personal best performance was identified in the official competition records. Personal best performances were ranked in percentiles and top-level athletes were considered those in the highest 4% of the performance distribution.

RESULTS

Overall, when controlling for the age of entering competition, top-level athletes reached their personal best later (i.e., around 23-25 years old) for all events compared to the rest of the athletes. Moreover, regression analysis showed that entering competitions later was linked to better performances during adulthood. Also, only 17%-26% [90% CI] of the top-level adult athletes were considered as such when they were 14-17 years old.

CONCLUSIONS

Together, these findings suggest that early sport success is not a strong predictor of top-level performance at senior level. Entering sport-specific competitions later and lengthening the sports career at beyond 23-25 years of age may be important factors to reach top-level performance in sprint and throwing events.

Feasibility of implementing an outdoor walking break in Italian middle schools

Brief bouts of physical activity during the school day are an innovative method for increasing physical activity in the school setting. The purpose of the study was to investigate if the introduction of an outdoor active break, based on walking and running, in a middle school in Italy is feasible in terms of implementation (i.e., adherence, costs, safety) and acceptability (i.e., satisfaction, intent to continue use, perceived appropriateness). One hundred and forty students (aged 12 ± 1 years) and 20 teachers (aged 50 ± 8 years) participated in the activity for four months. The activity consisted of walking (or running) one kilometer outside the school buildings during the mid-morning. Data from questionnaires regarding the satisfaction with and the acceptability of the activity were collected.

The activity was safely performed three to four days a week, without any costs to the school or to students’ parents. Students and teachers were satisfied with the activity (positive answers from 95% and 89% of each group, respectively). Moreover, the teachers reported that the program was easy to organize and did not negatively influence their teaching activities. The intervention was easily and safely implemented, and it was considered suitable for the daily routine of an Italian middle school. Further studies are needed to examine its impact on physical activity levels and academic achievement.

The relative age effect is larger in Italian soccer top-level youth categories and smaller in Serie A

The relative age effect (RAE; i.e., an asymmetry in the birth distribution) is a bias observed in sport competitions that may favour relatively older athletes in talent identification. Therefore, the aim of this study was to investigate the presence of RAE in elite soccer players competing in the Italian championships, even considering the discriminations of younger and older Serie A players (in relation to the median age of the sample), and different positional roles (i.e., goalkeeper, defender, midfielder, forward) for each observed category. A total of 2051 players competing into the 2017–2018 Italian under-15 (n = 265), under-16 (n = 362), under-17 (n = 403), Primavera (n = 421) and Serie A (n = 600) championships were analysed. The birth-date distributions, grouped in four quartiles (i.e., January-March, Q1; April-June, Q2; July-September, Q3; October-December, Q4), were compared to a uniform distribution using Chi-squared analysis. The week of birth was analysed using Poisson regression. The results showed a large over-representation of players born in Q1 in all soccer player categories. However, the effect size of this trend resulted smaller as age increased. Individuals born in Q1 have about two-folds more chances to become a Serie A player compared to those born in Q4. The Poisson regression analysis showed that RAE was greater for defenders than for forwards among all categories. Therefore, a strongly biased selection emerged among elite soccer players competing in Italian championships, highlighting how young individuals born in the first three months have many more chances to become elite players compared to the others.

Muscular and metabolic responses to different Nordic walking techniques, when style matters

Due to poling action and upper body engagement, Nordic walking (NW) has additional health benefits with respect to conventional walking. The aim of this study was to evaluate the differences in muscle activation and metabolic responses between NW, performed with the technique suggested by NW instructors, and with some modifications in the way to move upper limb and poles. Ten NW instructors volunteered to walk on a treadmill at 5.5 km•h-1 in five conditions: walking (W), Nordic walking (NW), NW with a weak poling action (NWweak), with straight-upper limbs moving the shoulders (NWshoulder) and with elbow flexion-extension pattern and shoulder freezed (NWelbow). Poling forces, body segments and poles movement, upper and lower body muscle activation, as well as metabolic parameters were measured.All modified NW techniques elicited lower muscular activation and metabolic responses with respect to the suggested NW technique (P < 0.05). All NW techniques elicited higher muscular activation and metabolic responses than W. All parameters observed with the NWweak were lower than NW. A decreased activation of shoulder extensor muscles and increased activation of anterior deltoid muscle were the main features of NWshoulder. Lower triceps brachii muscle activation and reduced propulsive poling action with respect to NW were seen for NWelbow, resulting also in shorter steps.Nordic walking instructors, sport technicians and practitioners should be aware that any deviation from the technique usually suggested might lead to lower benefits. However it is worth to note that any walking technique with poles elicits higher metabolic responses and muscular activation than walking.

Women show similar central and peripheral fatigue to men after half-marathon

Women are known to be less fatigable than men in single-joint exercises, but fatigue induced by running has not been well understood. Here we investigated sex differences in central and peripheral fatigue and in rate of force development (RFD) in the knee extensors after a half-marathon run. Ten male and eight female amateur runners (aged 25-50 years) were evaluated before and immediately after a half-marathon race. Knee extensors forces were obtained under voluntary and electrically evoked isometric contractions. Maximal voluntary isometric contraction (MVC) force and peak RFD were recorded. Electrically doublet stimuli were delivered during the MVC and at rest to calculate the level of voluntary activation and the resting doublet twitch. After the race, decreases in MVC force (males: -11%, effect size [ES] 0.52; females: -11% ES 0.33), voluntary activation (males: -6%, ES 0.87; females: -4%, ES 0.72), and resting doublet twitch (males: -6%, ES 0.34; females: -8%, ES 0.30) were found to be similar between males and females. The decrease in peak RFD was found to be similar between males and females (males: -14%, ES 0.43; females: -15%, ES 0.14). Half-marathon run induced both central and peripheral fatigue, without any difference between men and women. The maximal and explosive strength loss was found similar between sexes. Together, these findings do not support the need of sex-specific training interventions to increase the tolerance to neuromuscular fatigue in half-marathoners.

Validation of the ADAMO Care Watch for step counting in older adults

Background

Accurate measurement devices are required to objectively quantify physical activity. Wearable activity monitors, such as pedometers, may serve as affordable and feasible instruments for measuring physical activity levels in older adults during their normal activities of daily living. Currently few available accelerometer-based steps counting devices have been shown to be accurate at slow walking speeds, therefore there is still lacking appropriate devices tailored for slow speed ambulation, typical of older adults.

This study aimed to assess the validity of step counting using the pedometer function of the ADAMO Care Watch, containing an embedded algorithm for measuring physical activity in older adults.

Methods

Twenty older adults aged ≥ 65 years (mean ± SD, 75±7 years; range, 68–91) and 20 young adults (25±5 years, range 20–40), wore a care watch on each wrist and performed a number of randomly ordered tasks: walking at slow, normal and fast self-paced speeds; a Timed Up and Go test (TUG); a step test and ascending/descending stairs. The criterion measure was the actual number of steps observed, counted with a manual tally counter. Absolute percentage error scores, Intraclass Correlation Coefficients (ICC), and Bland–Altman plots were used to assess validity.

Results

ADAMO Care Watch demonstrated high validity during slow and normal speeds (range 0.5–1.5 m/s) showing an absolute error from 1.3% to 1.9% in the older adult group and from 0.7% to 2.7% in the young adult group. The percentage error for the 30-metre walking tasks increased with faster pace in both young adult (17%) and older adult groups (6%). In the TUG test, there was less error in the steps recorded for older adults (1.3% to 2.2%) than the young adults (6.6% to 7.2%). For the total sample, the ICCs for the ADAMO Care Watch for the 30-metre walking tasks at each speed and for the TUG test were ranged between 0.931 to 0.985.

Conclusion

These findings provide evidence that the ADAMO Care Watch demonstrated highly accurate measurements of the steps count in all activities, particularly walking at normal and slow speeds. Therefore, these data support the inclusion of the ADAMO Care Watch in clinical applications for measuring the number of steps taken by older adults at normal, slow walking speeds.

Career Performance Trajectories in Track and Field Jumping Events from Youth to Senior Success: The Importance of Learning and Development

INTRODUCTION

The idea that early sport success can be detrimental for long-term sport performance is still under debate. Therefore, the aims of this study were to examine the career trajectories of Italian high and long jumpers to provide a better understanding of performance development in jumping events.

METHODS

The official long-jump and high-jump rankings of the Italian Track and Field Federation were collected from the age of 12 to career termination, for both genders from the year 1994 to 2014. Top-level athletes were identified as those with a percentile of their personal best performance between 97 and 100.

RESULTS

The age of entering competitions of top-level athletes was not different than the rest of the athletic population, whereas top-level athletes performed their personal best later than the rest of the athletes. Top-level athletes showed an overall higher rate of improvement in performance from the age of 13 to the age of 18 years when compared to all other individuals. Only 10-25% of the top-level adult athletes were top-level at the age of 16. Around 60% of the top-level young at the age of 16 did not maintain the same level of performance in adulthood. Female high-jump represented an exception from this trend since in this group most top-level young become top-level adult athletes.

CONCLUSIONS

These findings suggest that performance before the age of 16 is not a good predictor of adult performance in long and high jump. The annual rate of improvements from 13 to 18 years should be included as a predictor of success rather than performance per se. Coaches should be careful about predicting future success based on performances obtained during youth in jumping events.

Decrease of muscle fiber conduction velocity correlates with strength loss after an endurance run

Monitoring surface electromyographic (EMG) signals can provide useful insights for characterizing muscle fatigue, which is defined as an exercise-induced strength loss. This experiment investigated the muscle fiber conduction velocity (CV) changes induced by an endurance run. The day before and immediately after a half-marathon run (21.097 km) 11 amateur runners performed maximum voluntary contractions (MVCs) of knee extensor muscles. During the MVC, multichannel EMG was recorded from the vastus lateralis and EMG amplitude and CV were calculated. After the run, knee extensors showed a decreased strength (-13  ±  9%, p  =  0.001) together with a reduction in EMG amplitude (-13  ±  10%, p  =  0.003) and in CV (-6  ±  8%, p  =  0.032). Knee extensor strength loss positively correlated with vastus lateralis CV differences (r  =  0.76, p  =  0.006). Thus, the exercises-induced muscle fatigue was associated not only with a decrease in EMG amplitude, but also with a reduction in CV. This finding suggests that muscle fibers with higher CV (i.e. those with greater fiber size) were the most impaired during strength production after an endurance run.

Motor unit firing rates and synchronisation affect the fractal dimension of simulated surface electromyogram during isometric/isotonic contraction of vastus lateralis muscle

During fatiguing contractions, many adjustments in motor units behaviour occur: decrease in muscle fibre conduction velocity; increase in motor units synchronisation; modulation of motor units firing rate; increase in variability of motor units inter-spike interval. We simulated the influence of all these adjustments on synthetic EMG signals in isometric/isotonic conditions. The fractal dimension of the EMG signal was found mainly influenced by motor units firing behaviour, being affected by both firing rate and synchronisation level, and least affected by muscle fibre conduction velocity. None of the calculated EMG indices was able to discriminate between firing rate and motor units synchronisation.

Central and peripheral fatigue in knee and elbow extensor muscles after a long-distance cross-country ski race

Although elbow extensors (EE) have a great role in cross-country skiing (XC) propulsion, previous studies on neuromuscular fatigue in long-distance XC have investigated only knee extensor (KE) muscles. In order to investigate the origin and effects of fatigue induced by long-distance XC race, 16 well-trained XC skiers were tested before and after a 56-km classical technique race. Maximal voluntary isometric contraction (MVC) and rate of force development (RFD) were measured for both KE and EE. Furthermore, electrically evoked double twitch during MVC and at rest were measured. MVC decreased more in KE (-13%) than in EE (-6%, P = 0.016), whereas the peak RFD decreased only in EE (-26%, P = 0.02) but not in KE. The two muscles showed similar decrease in voluntary activation (KE -5.0%, EE -4.8%, P = 0.61) and of double twitch amplitude (KE -5%, EE -6%, P = 0.44). A long-distance XC race differently affected the neuromuscular function of lower and upper limbs muscles. Specifically, although the strength loss was greater for lower limbs, the capacity to produce force in short time was more affected in the upper limbs. Nevertheless, both KE and EE showed central and peripheral fatigue, suggesting that the origins of the strength impairments were multifactorial for the two muscles.

Hand grip strength and anthropometric characteristics in Italian female national basketball teams

BACKGROUND

The aim of this study was to investigate the influence of hand and body dimensions on hand grip strength and to define a reference scale for talent identification in basketball players.

METHODS

Body and hand anthropometric data and the maximal handgrip strength of 109 female Italian basketball National players (Under14-Seniores) were measured.

RESULTS

Handgrip strength and arm length trend increased, raising the statistical significant differences only for players from the age of 19 (U20, Seniores) with respect to sub-elite groups (U14, U15) (P<0.05). Handgrip strength showed low positive correlations with height and Body Mass Index but a positive relationships with arm length (r=0.5; P<0.001). Findings underline training and years of practice have effects on increasing handgrip strength.

CONCLUSIONS

Data show that to select female basketball players by arm length means selecting by handgrip strength. Thus it is possible to suggest that in addition to height, arm length could also be considered a useful parameter in young female talent identification.

Higher Neuromuscular Manifestations of Fatigue in Dynamic than Isometric Pull-Up Tasks in Rock Climbers

Neuromuscular assessment of rock climbers has been mainly focused on forearm muscles in the literature. We aimed to extend the body of knowledge investigating on two other upper limb muscles during sport-specific activities in nine male rock climbers. We assessed neuromuscular manifestations of fatigue recording surface electromyographic signals from brachioradialis and teres major muscles, using multi-channel electrode arrays. Participants performed two tasks until volitional exhaustion: a sequence of dynamic pull-ups and an isometric contraction sustaining the body at half-way of a pull-up (with the elbows flexed at 90°). The tasks were performed in randomized order with 10 minutes of rest in between. The normalized rate of change of muscle fiber conduction velocity was calculated as the index of fatigue. The time-to-task failure was significantly shorter in the dynamic (31 ±10 s) than isometric contraction (59 ±19 s). The rate of decrease of muscle fiber conduction velocity was found steeper in the dynamic than isometric task both in brachioradialis (isometric: −0.2 ±0.1%/s; dynamic: −1.2 ±0.6%/s) and teres major muscles (isometric: −0.4±0.3%/s; dynamic: −1.8±0.7%/s). The main finding was that a sequence of dynamic pull-ups lead to higher fatigue than sustaining the body weight in an isometric condition at half-way of a pull-up. Furthermore, we confirmed the possibility to properly record physiological CV estimates from two muscles, which had never been studied before in rock climbing, in highly dynamic contractions.