Did you know? Using entropy and fractal geometry to quantify fluctuations in physiological outputs

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Fatigue-induced changes in knee-extensor torque complexity and muscle metabolic rate are dependent on joint angle

Purpose Joint angle is a signifcant determinant of neuromuscular and metabolic function. We tested the hypothesis that previously reported correlations between knee-extensor torque complexity and metabolic rate (mVȮ 2) would be conserved at reduced joint angles (i.e. shorter muscle lengths). Methods Eleven participants performed intermittent isometric knee-extensor contractions at 50% maximum voluntary torque for 30 min or until task failure (whichever occurred sooner) at joint angles of 30º, 60º and 90º of fexion (0º=extension). Torque and surface EMG were sampled continuously. Complexity and fractal scaling of torque were quantifed using approximate entropy (ApEn) and detrended fuctuation analysis (DFA) α. mVȮ 2 was determined using near-infrared spectroscopy. Results Time to task failure/end increased as joint angle decreased (P<0.001). Over time, complexity decreased at 90º and 60º (decreased ApEn, increased DFA α, both P<0.001), but not 30º. mVȮ 2 increased at all joint angles (P<0.001), though the magnitude of this increase was lower at 30º compared to 60º and 90º (both P<0.01). There were signifcant correlations between torque complexity and mVȮ 2 at 90º (ApEn, r= −0.60, P=0.049) and 60º (ApEn, r= −0.64, P=0.035; DFA α, ρ=0.68, P=0.015). Conclusion The lack of correlation between mVȮ 2 and complexity at 30º was likely due to low relative task demands, given the similar kinetics of mVȮ 2 and torque complexity. An inverse correlation between mVȮ 2 and knee-extensor torque complexity occurs during high-intensity contractions at intermediate, but not short, muscle lengths

Physiological complexity: influence of ageing, disease and neuromuscular fatigue on muscle force and torque fluctuations

New Findings: What is the topic of this review? Physiological complexity in muscle force and torque fluctuations, specifically the quantification of complexity, how neuromuscular complexityis altered by perturbations and the potential mechanism underlying changes in neuromuscular complexity. What advances does it highlight? The necessity to calculate both magnitude- and complexity-based measures for the thorough evaluation of force/torque fluctuations. Also the need for further research on neuromuscular complexity, particularly how it relates to the performance of functional activities (e.g. manual dexterity, balance, locomotion). Abstract: Physiological time series produce inherently complex fluctuations. In the last 30 years, methods have been developed to characterise these fluctuations, and have revealed that they contain information about the function of the system producing them. Two broad classes of metrics are used: (1) those which quantify the regularity of the signal (e.g. entropy metrics); and (2) those which quantify the fractal properties of the signal (e.g. detrended fluctuation analysis). Using these techniques, it has been demonstrated that ageing results in a loss of complexity in the time series of a multitude of signals, including heart rate, respiration, gait and, crucially, muscle force or torque output. This suggests that as the body ages, physiological systems become less adaptable (i.e. the systems’ ability to respond rapidly to a changing external environment is diminished). More recently, it has been shown that neuromuscular fatigue causes a substantial loss of muscle torque complexity, a process that can be observed in a few minutes, rather than the decades it requires for the same system to degrade with ageing. The loss of torque complexity with neuromuscular fatigue appears to occur exclusively above the critical torque (at least for tasks lasting up to 30 min). The loss of torque complexity can be exacerbated with previous exercise of the same limb, and reduced by the administration of caffeine, suggesting both peripheral and central mechanisms contribute to this loss. The mechanisms underpinning the loss of complexity are not known but may be related to altered motor unit behaviour as the muscle fatigues

The influence of heel pad confinement on heel pad mechanical properties

This study examined the effects of different amounts of heel pad confinement on the mechanical behaviour of the human heel pad. Confinement can be manipulated in two ways: containment defined as the act of heel pad confinement by an external device (representing the heel counter) from the impact surface superiorly, and exposure defined as the amount of heel pad left unconfined distally before the start of the containment device. It is hypothesised that with greater containment, the heel pad will demonstrate less maximal deformation and increased heel pad stiffness compared with the uncontained heel pad. With increasing exposure, it is hypothesised that the heel pad will demonstrate greater maximum deformation and decreased heel pad stiffness compared with the uncontained heel pad. Cadaver heel pads were compressed using loading profiles based on vertical ground reaction force profiles collected from 11 subjects running at their preferred running velocities. Ten cadaver heel pads were each loaded 60 times to peak forces scaled to body weight with a constant time interval between loadings, under different conditions of containment and exposure. Statistical comparisons indicated that fully containing the human heel pad significantly alters the heel pad mechanical behaviour by decreasing the maximum deformation and increasing its stiffness. Thus, these results supported the first hypothesis. Statistical comparisons indicated that partially exposing human heel pad significantly alters the heel pad mechanical behaviour by decreasing the maximum deformation and increasing its stiffness, to a greater extent than fully containing the heel pad. These results are the reverse of the predictions of the second hypothesis. Overall these results have implications for heel pad mechanical behaviour when shod, and for footwear design

Anticipation of landing leg masks ankle inversion orientation deficits and peroneal insufficiency during jump landing in people with chronic ankle instability

Ankle inversion orientation and peroneal activation insufficiency may contribute to lateral ankle sprains during landing in chronic ankle instability (CAI), however, how anticipation alters these factors is neglected. This study aimed to assess the impact of anticipation on joint orientation and muscle activity during landing in individuals with CAI. Fifteen participants with CAI and fifteen healthy participants (control) were recruited to perform single-leg landings after bilateral countermovement jumps when the landing limb was specified before (planned) or after (unplanned) take-off. Joint angle (hip, knee, and ankle) and electromyography (gluteus medius, rectus femoris, biceps femoris, gastrocnemius lateral head, tibialis anterior, peroneal longus) were collected and analysed with 2 (groups) x 2 (conditions) statistical parametric mapping ANOVA. In the unplanned condition, the CAI group demonstrated a less plantarflexed (maximum difference = 9.5˚, p=0.047) and more inverted ankle joint (maximum difference = 4.1˚, p<0.001) before ground contact, along with lower peroneal activity at ground contact compared to the control group (maximum difference = 28.9 % of peak activation, p<0.001). No significant differences between groups were observed in the planned condition. In conclusion, anticipation may mask jump landing deficits in people with CAI, including inverted ankle orientation and reduced peroneus longus activity pre- and post-landing, which were observed exclusively in unplanned landings. Clinicians and researchers need to recognize the impact of anticipation on apparent landing deficits and consider the implications for injury prevention and rehabilitation strategies.</p

Novel real-time OEP phase angle feedback system for dysfunctional breathing pattern training—an acute intervention study

Dysfunctional breathing patterns (DBP) can have an impact on an individual’s quality of life and/or exercise performance. Breathing retraining is considered to be the first line of treatment to correct breathing pattern, for example, reducing ribcage versus abdominal movement asynchrony. Optoelectronic plethysmography (OEP) is a non-invasive 3D motion capture technique that measures the movement of the chest wall. The purpose of this study was to investigate if the use of a newly developed real-time OEP phase angle and volume feedback system, as an acute breathing retraining intervention, could result in a greater reduction of phase angle values (i.e., an improvement in movement synchrony) when compared to real-time OEP volume feedback alone. Eighteen individuals with a DBP performed an incremental cycle test with OEP measuring chest wall movement. Participants were randomly assigned to either the control group, which included the volume-based OEP feedback or to the experimental group, which included both the volume-based and phase angle OEP feedback. Participants then repeated the same cycle test using the real-time OEP feedback. The phase angle between the ribcage versus abdomen (RcAbPhase), between the pulmonary ribcage and the combined abdominal ribcage and abdomen (RCpAbPhase), and between the abdomen and the shoulders (AbSPhase) were calculated during both cycle tests. Significant increases in RcAbPhase (pre: −2.89°, post: −1.39°, p < 0.01), RCpAbPhase (pre: −2.00°, post: −0.50°, p < 0.01), and AbSPhase (pre: −2.60°, post: −0.72°, p < 0.01) were found post-intervention in the experimental group. This indicates that the experimental group demonstrated improved synchrony in their breathing pattern and therefore, reverting towards a healthy breathing pattern. This study shows for the first time that dysfunctional breathing patterns can be acutely improved with real-time OEP phase angle feedback and provides interesting insight into the feasibility of using this novel feedback system for breathing pattern retraining in individuals with DBP

Anticipation of landing leg masks ankle inversion orientation deficits and peroneal insufficiency during jump landing in people with chronic ankle instability

Ankle inversion orientation and peroneal activation insufficiency may contribute to lateral ankle sprains during landing in chronic ankle instability (CAI), however, how anticipation alters these factors is neglected. This study aimed to assess the impact of anticipation on joint orientation and muscle activity during landing in individuals with CAI. Fifteen participants with CAI and fifteen healthy participants (control) were recruited to perform single-leg landings after bilateral countermovement jumps when the landing limb was specified before (planned) or after (unplanned) take-off. Joint angle (hip, knee, and ankle) and electromyography (gluteus medius, rectus femoris, biceps femoris, gastrocnemius lateral head, tibialis anterior, peroneal longus) were collected and analysed with 2 (groups) x 2 (conditions) statistical parametric mapping ANOVA. In the unplanned condition, the CAI group demonstrated a less plantarflexed (maximum difference = 9.5˚, p=0.047) and more inverted ankle joint (maximum difference = 4.1˚, p<0.001) before ground contact, along with lower peroneal activity at ground contact compared to the control group (maximum difference = 28.9 % of peak activation, p<0.001). No significant differences between groups were observed in the planned condition. In conclusion, anticipation may mask jump landing deficits in people with CAI, including inverted ankle orientation and reduced peroneus longus activity pre- and post-landing, which were observed exclusively in unplanned landings. Clinicians and researchers need to recognize the impact of anticipation on apparent landing deficits and consider the implications for injury prevention and rehabilitation strategies.</p

Pressure generated by the modern human hand during vertical climbing [Abstract]

Conference abstract: Pressure generated by the modern human hand during vertical climbing.</p