Effects of short-term fatigue on biomechanical and physiological aspects of double poling in high-level cross-country skiers

The study aim was to evaluate biomechanical and physiological alterations in double poling technique (DP) after a short-term fatiguing exercise. Eight high-level skiers performed a sub-maximal DP trial (20 km h⁻¹, 1°) before (PRE) and after (POST) a DP test to exhaustion while roller skiing on a treadmill. An integrated analysis of DP technique during PRE and POST included measurement of pole, joint, and centre of mass (COM) kinematics, poling forces, cycle timing, and metabolic parameters. Muscle fatigue in three upper-body muscles was assessed by calculating the Dimitrov’ fatigue index (FI_nms5) of specific electromyographic segments. FI_nms5 tended to increase in the latissimus dorsi and teres major muscles (P = 0.023 and P = 0.030, respectively) across consecutive DP cycles, as did blood lactate concentration (P = 0.001) and rating of perceived exertion (P = 0.005). The changes indicated a state of fatigue during POST and coincided with the reduction in poling force exertion capacity (P = 0.020). Pole, joint and COM kinematics did not differ between PRE and POST (P > 0.050), whereas recovery phase and cycle times were shorter at POST (P < 0.001 and P = 0.001, respectively). Short-term fatigue led to a reduction in poling force exertion capacity and cycle time in high-level skiers, without altering body and pole kinematics.     

Fatigue-induced dissociation between rate of force development and maximal force across repeated rapid contractions

We examined whether the presence of fatigue induced by prolonged running influenced the time courses of force generating capacities throughout a series of intermittent rapid contractions. Thirteen male amateur runners performed a set of 15 intermittent isometric rapid contractions of the knee extensor muscles, (3 s/5 s on/off) the day before (PRE) and immediately after (POST) a half marathon. The maximal voluntary contraction force, rate of force development (RFD_peak), and their ratio (relative RFD_peak) were calculated. At POST, considering the first (out of 15) repetition, the maximal force and RFD_peak decreased (p < 0.0001) at the same extent (by 22 ± 6% and 24 ± 22%, respectively), resulting in unchanged relative RFD_peak (p = 0.6). Conversely, the decline of RFD_peak throughout the repetitions was more pronounced at POST (p = 0.02), thus the decline of relative RFD_peak was more pronounced (p = 0.007) at POST (−25 ± 13%) than at PRE (−3 ± 13%). The main finding of this study was that the fatigue induced by a half-marathon caused a more pronounced impairment of rapid compared to maximal force in the subsequent intermittent protocol. Thus, the fatigue-induced impairment in rapid muscle contractions may have a greater effect on repeated, rather than on single, attempts of maximal force production.     

Kinematic and ground reaction force accommodation during weighted walking

Weighted walking is a functional activity common in daily life and can influence risks for musculoskeletal loading, injury and falling. Much information exists about weighted walking during military, occupational and recreational tasks, but less is known about strategies used to accommodate to weight carriage typical in daily life. The purposes of the study were to examine the effects of weight carriage on kinematics and peak ground reaction force (GRF) during walking, and explore relationships between these variables. Twenty subjects walked on a treadmill while carrying 0, 44.5 and 89 N weights in front of the body. Peak GRF, sagittal plane joint/segment angular kinematics, stride length and center of mass (COM) vertical displacement were measured. Changes in peak GRF and displacement variables between weight conditions represented accommodation. Effects of weight carriage were tested using analysis of variance. Relationships between peak GRF and kinematic accommodation variables were examined using correlation and regression. Subjects were classified into sub-groups based on peak GRF responses and the correlation analysis was repeated. Weight carriage increased peak GRF by an amount greater than the weight carried, decreased stride length, increased vertical COM displacement, and resulted in a more extended and upright posture, with less hip and trunk displacement during weight acceptance. A GRF increase was associated with decreases in hip extension (|r| = .53, p = .020) and thigh anterior rotation (|r| = .57, p = .009) displacements, and an increase in foot anterior rotation displacement (|r| = .58, p = .008). Sub-group analysis revealed that greater GRF increases were associated with changes at multiple sites, while lesser GRF increases were associated with changes in foot and trunk displacement. Weight carriage affected walking kinematics and revealed different accommodation strategies that could have implications for loading and stability.     

Variability of a “force signature” during windmill softball pitching and relationship between discrete force variables and pitch velocity

This study assessed reliability of discrete ground reaction force (GRF) variables over multiple pitching trials, investigated the relationships between discrete GRF variables and pitch velocity (PV) and assessed the variability of the “force signature” or continuous force-time curve during the pitching motion of windmill softball pitchers. Intraclass correlation coefficient (ICC) for all discrete variables was high (0.86–0.99) while the coefficient of variance (CV) was low (1.4–5.2%). Two discrete variables were significantly correlated to PV; second vertical peak force (r(5) = 0.81, p = 0.03) and time between peak forces (r(5) = −0.79; p = 0.03). High ICCs and low CVs support the reliability of discrete GRF and PV variables over multiple trials and significant correlations indicate there is a relationship between the ability to produce force and the timing of this force production with PV. The mean of all pitchers’ curve-average standard deviation of their continuous force-time curves demonstrated low variability (CV = 4.4%) indicating a repeatable and identifiable “force signature” pattern during this motion. As such, the continuous force-time curve in addition to discrete GRF variables should be examined in future research as a potential method to monitor or explain changes in pitching performance.     

Evidence of muscular adaptations within four weeks of barbell training in women

We investigated the time course of neuromuscular and hypertrophic adaptations associated with only four weeks of barbell squat and deadlift training. Forty-seven previously untrained women (mean ± SD, age = 21 ± 3 years) were randomly assigned to low volume training (n = 15), moderate volume training (n = 16), and control (n = 16) groups. The low and moderate volume training groups performed two and four sets, respectively, of five repetitions per exercise, twice a week. Testing was performed weekly, and included dual X-ray absorptiometry and vastus lateralis and rectus femoris B-mode ultrasonography. Bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis and biceps femoris during isometric maximal voluntary contractions of the leg extensors. Significant increases in lean mass for the combined gynoid and leg regions for the low (+0.68 kg) and moderate volume (+0.47 kg) groups were demonstrated within three weeks. Small-to-moderate effect sizes were shown for leg lean mass, vastus lateralis thickness and pennation angle, and peak torque, but EMG amplitude was unaffected. These findings demonstrated rapid muscular adaptations in response to only eight sessions of back squat and deadlift training in women despite the absence of changes in agonist–antagonist EMG amplitude.     

The role of motion platform on postural instability and head vibration exposure at driving simulators

This paper explains the effect of a motion platform for driving simulators on postural instability and head vibration exposure. The sensed head level-vehicle (visual cues) level longitudinal and lateral accelerations (a_x,sensed = a_{x_head} and a_y,sensed = a_{y_head}, a_yv = a_{y_veh} and a_yv = a_{y_veh}) were saved by using a motion tracking sensor and a simulation software respectively. Then, associated vibration dose values (VDVs) were computed at head level during the driving sessions. Furthermore, the postural instabilities of the participants were measured as longitudinal and lateral subject body centre of pressure (X_CP and Y_CP, respectively) displacements just after each driving session via a balance platform. The results revealed that the optic-head inertial level longitudinal accelerations indicated a negative non-significant correlation (r = −.203, p = .154 > .05) for the static case, whereas the optic-head inertial longitudinal accelerations depicted a so small negative non-significant correlation (r = −.066, p = .643 > .05) that can be negligible for the dynamic condition. The X_CP for the dynamic case indicated a significant higher value than the static situation (t(47), p < .0001). The VDV_x for the dynamic case yielded a significant higher value than the static situation (U(47), p < .0001). The optic-head inertial lateral accelerations resulted a negative significant correlation (r = −.376, p = .007 < .05) for the static platform, whereas the optic-head inertial lateral accelerations showed a positive significant correlation (r = .418, p = .002 < .05) at dynamic platform condition. The VDV_y for the static case indicated a significant higher value rather than the dynamic situation (U(47), p < .0001). The Y_CP for the static case yielded significantly higher than the dynamic situation (t(47), p = .001 < 0.05).     

The effect of swinging the arms on muscle activation and production of leg force during ski skating at different skiing speeds

The study investigated the effects of arm swing during leg push-off in V2-alternate/G4 skating on neuromuscular activation and force production by the leg muscles. Nine skilled cross-country skiers performed V2-alternate skating without poles at moderate, high, and maximal speeds, both with free (SWING) and restricted arm swing (NOSWING). Maximal speed was 5% greater in SWING (P < 0.01), while neuromuscular activation and produced forces did not differ between techniques. At both moderate and high speed the maximal (2% and 5%, respectively) and average (both 5%) vertical force and associated impulse (10% and 14%) were greater with SWING (all P < 0.05). At high speed range of motion and angular velocity of knee flexion were 24% greater with SWING (both P < 0.05), while average EMG of m. biceps femoris was 31% lower (all P < 0.05) in SWING. In a similar manner, the average EMG of m. vastus medialis and m. biceps femoris were lower (17% and 32%, P < 0.05) during the following knee extension. Thus, swinging the arms while performing V2-alternate can enhance both maximal speed and skiing economy at moderate and, in particularly, high speeds.     

The Supraspinatus and the Deltoid – Not just two arm elevators

BackgroundThe debate on the clinical and functional role of the Supraspinatus in relation to the Deltoid necessitates experimental assessment of their contributions to arm elevation. Our goal was to evaluate the responses of both muscles to increased elevation moment loading.MethodsTwenty-three healthy volunteers applied 30 N elevation forces at the proximal and distal humerus, resulting in small and large glenohumeral elevation moment tasks. The responses of the Deltoid and Supraspinatus were recorded with surface and fine-wire electromyography, quantified by (EMG_distal − EMG_proximal), and normalized by the summed activations (EMG_distal + EMG_proximal) to R_Muscle ratios.ResultsDeltoid activity increased with large elevation moment loading (R_DE = .11, 95%-CI [.06–.16]). Surprisingly, there was no significant average increase in Supraspinatus activation (R_SSp = .06, 95%-CI [−.08 to .20]) and its response was significantly more variable (Levene’s test, F = 11.7, p < .001). There was an inverse association between the responses (ß = −1.02, 95%-CI [−2.37 to .32]), indicating a potential complementary function of the Supraspinatus to the Deltoid.ConclusionThe Deltoid contributes to the glenohumeral elevation moment, but the contribution of the Supraspinatus is variable. We speculate there is inter-individual or intra-muscular function variability for the Supraspinatus, which may be related to the frequently reported variations in symptoms and treatment outcome of Supraspinatus pathologies.     

Comparison of trunk muscle reflex activation patterns between active and passive trunk flexion–extension loading conditions

The aim of the present study was to determine the effects of trunk flexion–extension loading on the neuromuscular reflexive latencies and amplitude responses of the trunk musculature. Eighteen male and female subjects (18–27 yrs) participated in active and passive trunk flexion extension, performed ∼7 days apart. Subjects performed 60 trunk flexion–extension repetitions. Surface electromyography (EMG) was collected bilaterally from paraspinal and abdominal muscles. In the active condition, subjects volitionally moved their trunks, while in the passive condition the dynamometer controlled the movements. The trunk was perturbed before and immediately after 30 repetitions. Latency of muscle onset, latency of first peak, latency of maximum peak, and peak EMG amplitude were evaluated. No differences between conditions, sides, or perturbation session were apparent. Overall latencies were shorter in females (p < .05) and abdominal muscles compared to paraspinals (p < .05). Thoracic paraspinal muscle amplitudes were greater than all other muscles (p < .05). Based upon the present results, the neuromuscular system engages trunk flexor muscles prior to the paraspinals in order to provide possible stabilization of the trunk when flexor moments are generated. Overall, the results indicate no difference in response of the neuromuscular system to active or passive repetitive loading.     

Dynamic touch is affected in children with cerebral palsy

Children with developmental disorders such as cerebral palsy have limited opportunities for effortful interactions with objects and tools. The goal of the study was to investigate whether children with cerebral palsy have deficits in their ability to perceive object length by dynamic touch when compared to typically developing children. Fourteen children with typical development and 12 children with cerebral palsy were asked to report the length of hand-held rods after wielding them out of sight. Multilevel regression models indicated that I₁ (maximum principal moment of inertia) was a significant predictor of perceived length – L_P (p < .0001). The effect of I₁ on L_P was significantly different among children (p = .001) and the presence of cerebral palsy (group factor) partially explained such variance (p = .002). In addition, accuracy and reliability of the length judgments made by children with cerebral palsy were significantly lower than the typically developing children (p < .05). Theoretical and clinical implications of these results were identified and discussed.     

Adaptation of lower limb movement patterns when maintaining performance in the presence of muscle fatigue

Adaptations in lower limb movement patterns were examined when performance was maintained during a fatiguing repetitive loading task. Forty recreationally active male and female participants performed single-leg hopping to volitional exhaustion at 2.2 Hz to a submaximal height. Spatio-temporal characteristics, mechanical characteristics and variability of the knee-ankle and hip-knee joint couplings were determined at 20% increments during the duration of the hopping task. Variability of the knee-ankle and hip-knee couplings in the flexion/extension axis significantly increased during the loading and propulsion phases during the hopping task (p < 0.05). Performance (vertical stiffness, hopping frequency and height) did not change significantly during the task (p > 0.05), however foot contact time increased progressively during this task (p < 0.05) and maximum hop height significantly decreased after the task (p < 0.05). The observed increase in variability between adjoining lower limb segments demonstrated the ability of the neuromotor system to adapt and maintain performance even with the onset of fatigue. This finding highlights that during the performance of a rapid and repetitive loading activity, performance can be preserved when there is variability in the neuromotor system.     

Modulation of motor variability related to experimental muscle pain during elbow-flexion contractions

Experimental muscle pain typically reorganizes the motor control. The pain effects may decrease when the three-dimensional force components are voluntarily adjusted, but it is not known if this could have negative consequences on other structures of the motor system. The present study assessed the effects of acute pain on the force variability during sustained elbow flexion when controlling task-related (one-dimensional) and all (three-dimensional) contraction force components via visual feedback. Experimental muscle pain was induced by bolus injection of hypertonic saline into m. biceps brachii, and isotonic saline was used as control. Twelve subjects performed sustained elbow flexion at different levels of the maximal voluntary contraction (5–30% MVC) before, during, and after the injections. Three-dimensional force components were measured simultaneously with surface electromyography (EMG) from elbow flexors and auxiliary muscles. Results showed that force variability was increased during pain compared to baseline for contractions using one-dimensional feedback (P < .05), but no significant differences were found for three-dimensional feedback. During painful contractions (1) EMG activity from m. trapezius was increased during contractions using both one-dimensional and three-dimensional feedback (P < .05), and (2) the complexity of EMG from m. triceps brachii and m. deltoid was higher for the three-dimensional feedback (P < .05). In conclusion, the three-dimensional feedback reduced the pain-related functional distortion at the cost of a more complex control of synergistic muscles.     

Explanatory models of muscle performance in acromegaly patients evaluated by knee isokinetic dynamometry: Implications for rehabilitation

PurposeTo evaluate the effects of demographics and hormonal variations on knee muscle performance in patients with acromegaly and develop explanatory models of peripheral muscle function in these individuals.MethodsThis was a cross-sectional study in which 53 acromegalics and 27 healthy subjects underwent knee isokinetic dynamometry to evaluate the peak torque value for leg extension at 75°/s (PTE75) and 240°/s (PTE240). Separate multivariable linear regression models for the prediction of PTE75 and PTE240 were tested using variables commonly used as predictors in the clinical setting and other specific variables related to acromegaly.ResultsThe final prediction model for PTE75 (R² = 0.888; adjusted R² = 0.820, SE of bias = 16.2 Nm, p < 0.001) was −0.221 × growth hormone + 36.791 × sex_male = 1 − 27.407 × status_active = 1 − 0.690 × age + 148.071. The final prediction model for PTE240 (R² = 0.816; adjusted R² = 0.805, SE of bias = 8.8 Nm, p < 0.001) was −0.174 × growth hormone + 12.522 × sex_male = 1 − 0.520 × age + 98.099.ConclusionsIn acromegalics, high growth hormone levels, female gender, and older age are associated with reduced muscle strength and endurance. Additionally, active disease negatively affects peripheral muscle strength in these patients.     

Relationships between coordination,active drag and propelling efficiency in crawl

This study examines the relationships between the index of coordination (IdC) and active drag (D) assuming that at constant average speed, average drag equals average propulsion. The relationship between IdC and propulsive efficiency (e_p) was also investigated at maximal speed. Twenty national swimmers completed two incremental speed tests swimming front crawl with arms only in free condition and using a measurement of active drag system. Each test was composed of eight 25-m bouts from 60% to 100% of maximal intensity whereby each lap was swum at constant speed. Different regression models were tested to analyse IdC–D relationship. Correlation between IdC and e_p was calculated. IdC was linked to D by linear regression (IdC = 0.246 · D − 27.06; R² = 0.88, P < .05); swimmers switched from catch-up to superposition coordination mode at a speed of ∼1.55 m s⁻¹ where average D is ∼110 N. No correlation between IdC and e_p at maximal speed was found. The intra-individual analysis revealed that coordination plays an important role in scaling propulsive forces with higher speed levels such that these are adapted to aquatic resistance. Inter-individual analysis showed that high IdC did not relate to a high e_p suggesting an individual optimization of force and power generation is at play to reach high speeds.     

Inbreeding depression and IQ in a study of 72 countries

In this ecological study, a robust negative correlation of r = ? .62 (P < .01) is reported between national IQs and consanguinity as measured by the log₁₀ transformed percentage of consanguineous marriages for 72 countries. This correlation is reduced in magnitude, when IQ is controlled for GDP per capita (r = ? .41, P < .01); education index (r = ? .40, P < .01); and democracy index (r = ? .42, P < .01). Multiple regression analysis revealed that in the absence of the democracy index; percentage consanguineous marriages, education index and GDP per capita all exhibited stable final standardized β coefficients, however consanguinity had the least impact (β = 0, P > .05) whereas GDP per capita had the highest (β = .35, P > .01). This result is interpreted in light of cultural feedback theory, whereby it is suggested that consanguinity could subtly influence IQ at larger scales as a result of small IQ handicaps bought about through inbreeding being amplified into much larger differences through their effect on factors that maximize IQ such as access to education and adequate nutrition. Finally, consideration is given to future potential research directions.     

Do developmental differences in mental toughness exist between specialized and invested Australian footballers?

Using a cross-sectional design, the primary purpose of the present study was to examine developmental differences in mental toughness between specialized and invested Australian footballers. A secondary purpose was to examine the psychometric properties of the Australian football Mental Toughness Inventory (AfMTI; Gucciardi, Gordon, & Dimmock, 2009a) with a sample of youth footballers. Participants were 350 footballers aged between 13 and 18 (M = 15.88; SD = 1.71); 144 (M_age = 14.06; SD = .89) and 206 (M_age = 17.02; SD = 1.06) footballers from the specialized and investment developmental stages, respectively. A confirmatory factor analysis of the AfMTI using AMOS did not reveal support for its psychometric structure; however, a revised version received support. A MANOVA revealed the presence of a significant difference between the two developmental groups, and follow-up ANOVA’s indicated that the desire success and sport awareness subscales contributed to multivariate effect. It appears that developmental differences should be considered in future theorizing on the development of mental toughness.     

Bidirectional pathways between relational aggression and temperament from late childhood to adolescence

Relational aggression is linked to numerous adverse consequences. However, we know little about how temperament leads individuals to become perpetrators/victims of relational aggression, or how being a perpetrator/victim influences the development of temperament. We used longitudinal data from 674 Mexican-origin youth to examine relations between relational aggression and mother- and child-reported temperament from 5th grade (M_age = 10.8; SD = 0.60) through 11th grade (M_age = 16.8; SD = 0.50). Results show that: (a) high Negative Emotionality and low Effortful Control predicted increases in victimization; (b) low Effortful Control predicted increases in perpetration; (c) victims increased in Negative Emotionality and decreased in Effortful Control; and (d) perpetrators increased in Negative Emotionality and Surgency. Thus, temperament serves as both an antecedent to and a consequence of relational aggression.     

Validation française d’une version brève de l’Échelle de satisfaction maritale

IntroductionFew measuring instruments of couple satisfaction maximizing the individual perception of the relationship exists in French. Settings such as Liaison psychiatry of a general hospital could benefit from a questionnaire adapting to a variety of clinical profiles.ObjectiveThis article proposes a French revision and validation of the Marital Satisfaction Scale (MSS; Roach, Frazier, and Bowden, 1981), a 48-item self-reported questionnaire designed to evaluate personal satisfaction towards one's couple relationship.MethodA sample of 349 community-dwelling individuals aged 20–85 answered the MSS, the Dyadic Adjustment Scale (DAS; Spanier, 1976), and a series of inquiries related to sociodemographics. As an initial Exploratory Factor Analysis (EFA) did not validate the unidimensional structure postulated by the original authors, the item number was reduced to 14.ResultsThis brief version of the scale (MSS-14) was subsequently validated with an internal replication analysis, a strong criterion-related validity with the DAS (r_s = 0.73, P < 0.001), an excellent internal consistency (α = 0.961, IC à 95% [0.955, 0.967]), a strong test-retest reliability (r_s = 0.90, CI à 95% [0.85, 0.93], P < 0.001, Z = − 0.033, P = 0.973), and strong item-to-total correlations (> 0.69). The MSS-14 could differentiate individuals with and without marital distress (AUC = 0.97), while no sociodemographic variable seemed to have a significant influence on couple satisfaction.ConclusionThe MSS-14 appears to be a reliable instrument to assess the personal satisfaction towards a couple relationship in community-dwelling adults.     

Local muscle oxygen consumption related to external and joint specific power

The purpose of the present study was to examine the effects of external work rate on joint specific power and the relationship between knee extension power and vastus lateralis muscle oxygen consumption (mVO₂). We measured kinematics and pedal forces and used inverse dynamics to calculate joint power for the hip, knee and ankle joints during an incremental cycling protocol performed by 21 recreational cyclists. Vastus lateralis mVO₂ was estimated using near-infrared spectroscopy with an arterial occlusion. The main finding was a non-linear relationship between vastus lateralis mVO₂ and external work rate that was characterised by an increase followed by a tendency for a levelling off (R² = 0.99 and 0.94 for the quadratic and linear models respectively, p < 0.05). When comparing 100 W and 225 W, there was a ∼43 W increase in knee extension but still a ∼9% decrease in relative contribution of knee extension to external work rate resulting from a ∼47 W increase in hip extension. When vastus lateralis mVO₂ was related to knee extension power, the relationship was still non-linear (R² = 0.99 and 0.97 for the quadratic and linear models respectively, p < 0.05). These results demonstrate a non-linear response in mVO₂ relative to a change in external work rate. Relating vastus lateralis mVO₂ to knee extension power showed a better fit to a linear equation compared to external work rate, but it is not a straight line.     

Emotional intelligence and risky driving behaviour in adults

BackgroundRisky driving is considered a key predictive factor in road traffic accidents resulting in morbidity and mortality. Intra-individual emotional and personality factors have been shown to influence risk-taking behaviours among drivers. Despite this, there is limited research investigating the individual dimensions of these constructs and their relationship to risky driving behaviour (RDB). The current study therefore aimed to assess whether the individual dimensions of Emotional Intelligence (EI) were implicated in RDB.MethodsThe sample comprised 179 adults (55% male) aged between 18 and 64 years (M = 29.85, SD = 11.46) and who currently held a valid driver’s licence completed an online survey. Emotional Intelligence was assessed via self-report using the Swinburne University Emotional Intelligence Test (SUEIT), and RDB was measured using both the Brief Distracted Driving Scale (BDDS) and the Dula Dangerous Driving Index (DDDI).ResultsRegression analyses revealed that ‘Risky Driving’ was related to greater levels of Emotional Recognition and Expression and lesser Age [F_{(6, 172)} = 2.27, p < 0.05: R² = 7.3%], and the Negative Emotions sub-scale of DDDI, was significantly predicted by Emotional Control and Age [F_{(6, 172)} = 6.41, p < 0.05: R² = 18.3%]. A mediation model incorporating Age, Emotional Control scores and the Negative Emotions driving behaviour score indicated that a significant indirect effect of Age through Emotional Control (K² = 0.08, 95% CI [−0.02, −0.03]). (H [3] = 10.98, p = 0.012).ConclusionsLower scores on specific indices of EI are associated with increased rates of RDB, suggesting that poor emotional control may impede an individuals’ ability to make safe behavioural decisions when driving. The effect sizes for these models were small, however, and further research is needed to explore the contributory components in this association. Greater awareness of the role of emotional regulation and driving behaviours may be useful in preventing RDB in adults.