Changes in muscle and joint coordination in learning to direct forces

Active control of static pedal force direction decreases maximum isometric force output

Perfect mechanical force effectiveness in cycling would be achieved if the forces applied to the pedal were perpendicular to the crank throughout the full crank cycle. However, empirical observations show that resultant pedal forces display substantial radial components in recreational and even highly-trained elite cyclists. Therefore, we hypothesized that attempting to maximize mechanical effectiveness during the entire downstroke of the pedal cycle must be associated with a penalty that outweighs the benefits of perfect effectiveness. Twenty recreational cyclists performed maximum isometric voluntary contractions at five static crank positions in the downstroke phase of cycling for two testing conditions: (i) a non-constrained (NC) condition, where athletes were asked to produce the maximum force possible on the pedal without consideration of the force direction and (ii) a constrained (C) condition, with the instruction to produce maximal pedal forces perpendicular to the crank. Resultant force and effective force (force perpendicular to the crank in the NC conditions) were compared to the force in the C condition that was, by definition, perpendicular to the crank. Maximum effective force in the NC condition was greater (mean = 50 %, range = 38-69 %) than for the C condition across all crank positions. Applying forces perpendicular to the crank in the downstroke of the pedal cycle resulted in severe reductions in force magnitude, suggesting that coaches and athletes should not attempt to change cycling technique towards perfect force effectiveness.

Changes in Muscle Control After Learning to Direct Pedal Forces in One-Legged Pedaling

The aim of this study was to describe how major leg muscle activities are altered after learning a novel one-legged pedaling task. Fifteen recreational cyclists practiced one-legged pedaling trials during which they were instructed to match their applied pedal force to a target direction perpendicular to the crank arm. Activity in 10 major leg muscles was measured with surface electromyography electrodes. Improved upstroke task performance was obtained by greater activity in the hip and ankle flexor muscles, counteracting the negative effects of gravity. Greater quadriceps activities explained improved targeting near top dead center. Reduced uniarticular knee and ankle extensor downstroke activities were necessary to prevent freewheeling. Greater hamstring and tibialis anterior activities improved targeting performance near the bottom of the pedal stroke. The activity patterns of the biarticular plantarflexors changed little, likely due to their contributions as knee flexors for smooth upstroke pedaling motion. These results add to our understanding of how the degrees of freedom at the muscle level are altered in a cooperative manner to overcome gravitational effects in order to achieve the learning goal of the motor task while satisfying multiple constraints—in this case, the production of smooth one-legged pedaling motion at the designated mechanical task demands.

Muscular activity patterns in 1-legged vs. 2-legged pedaling

BACKGROUND

One-legged pedaling is of interest to elite cyclists and clinicians. However, muscular usage in 1-legged vs. 2-legged pedaling is not fully understood. Thus, the study was aimed to examine changes in leg muscle activation patterns between 2-legged and 1-legged pedaling.

METHODS

Fifteen healthy young recreational cyclists performed both 1-legged and 2-legged pedaling trials at about 30 Watt per leg. Surface electromyography electrodes were placed on 10 major muscles of the left leg. Linear envelope electromyography data were integrated to quantify muscle activities for each crank cycle quadrant to evaluate muscle activation changes.

RESULTS

Overall, the prescribed constant power requirements led to reduced downstroke crank torque and extension-related muscle activities (vastus lateralis, vastus medialis, and soleus) in 1-legged pedaling. Flexion-related muscle activities (biceps femoris long head, semitendinosus, lateral gastrocnemius, medial gastrocnemius, tensor fasciae latae, and tibialis anterior) in the upstroke phase increased to compensate for the absence of contralateral leg crank torque. During the upstroke, simultaneous increases were seen in the hamstrings and uni-articular knee extensors, and in the ankle plantarflexors and dorsiflexors. At the top of the crank cycle, greater hip flexor activity stabilized the pelvis.

CONCLUSION

The observed changes in muscle activities are due to a variety of changes in mechanical aspects of the pedaling motion when pedaling with only 1 leg, including altered crank torque patterns without the contralateral leg, reduced pelvis stability, and increased knee and ankle stiffness during the upstroke.

Neuromuscular activation pattern of lower extremity muscles during pedaling in cyclists with single amputation of leg and with two legs: a case study

Objective

In Para-cycling competitions, cyclists with amputation of one-leg and no prosthesis, i.e., Division Cycle, Sport Class C2, perform pedaling movement on bicycle by unilateral leg. The purpose of this study was to describe neuromuscular activation of lower extremity muscles in two cyclists with single leg amputation and one cyclist with two legs during pedaling. We compared averaged rectified values (ARV) of surface electromyography for lower extremity muscles during crank cycle for two single leg cyclists with one cyclist with two legs at 65%, 80%, and 95% of VO₂ max.

Results

Characteristic features of cyclists with single amputation of leg were increases in ARV for proximal region of the rectus femoris muscle in first half of pulling phase, increases in ARV for the biceps femoris muscle in first half of pulling phase, and increases in ARV for the medial gastrocnemius muscle in pulling phase. These findings in this study suggest that cyclists with single amputation of leg use characteristic neuromuscular coordination in the muscles contributing to hip and knee flexion joint moments during pulling phase and this may be the strategy in cyclists with single amputation of leg to compensate lack of hip and/or knee extension torque from contralateral leg.

Emphasizing one leg facilitates single-leg training using standard cycling equipment

PURPOSE

Single-leg cycling exercise is one of the most potent, but underutilized, stimuli for promoting peripheral muscle respiratory capacity. Special ergometers used to facilitate single-leg cycling, while maintaining biomechanics similar to double-leg cycling, are not widely available. This lack of availability of specialized ergometers may explain why single-leg cycling has not been widely implemented as standard clinical practice. Therefore, we explored the extent to which participants could emphasize one leg and de-emphasize the other to perform "single-leg emphasis cycling" using standard cycle ergometers.

METHODS

Sixteen athletic participants performed single-leg emphasis cycling, emphasizing each leg in separate trials, and double-leg cycling. Pedal forces and limb kinematics were collected and used to calculate joint-specific work and power at the ankle, knee, and hip.

RESULTS

Study participants were able to produce approximately three times as much power with their emphasized leg compared to the de-emphasized leg during single-leg emphasis cycling. Ankle plantar flexion, dorsiflexion, knee extension, and hip extension work produced during single-leg emphasis cycling did not differ from those during double-leg cycling (all P > .60). Hip and knee flexion work during single-leg emphasis cycling exhibited small but significant differences (both P < .05) from double-leg cycling.

CONCLUSIONS

These results demonstrate that single-leg emphasis cycling provides a convenient alternative to single-leg cycling requiring specialized ergometers, therefore, facilitating improved training in clinical and athletic populations using commonly available equipment. Further, biomechanics during single-leg emphasis cycling closely approximated double-leg cycling ensuring that training adaptations are highly applicable to double-leg cycling.

Strategies for improving the pedaling technique

INTRODUCTION

Pedaling technique which can be defined as the way the cyclists pedal, has been mostly studied in lab conditions from pedal force kinetic, joints kinematic, and/or muscular activity patterns because it is considered as a main factor for gross efficiency (GE). Although this method is much controversial, its quality has extensively been evaluated from the index of pedal force effectiveness (IFE), i.e. the ratio between the effective to the total pedal force. Over the last thirty years, preferred pedaling technique has been compared between the experienced cyclists and non-cyclists and also often been manipulated by instructing these subjects to improve their effective force production during the downstroke phase ("pushing"), the upstroke phase ("pulling-up") or around top and bottom dead centers ("circling").

EVIDENCE ACQUISITION

It has been shown that PREF pedaling technique is much repeatable across crank cycles in experienced cyclists than in novice cyclists. PULL involves a significant increase of IFE compared to PREF, mainly attributed to the increase of the muscular work of hip (RF) and knee flexors muscles (BF) during the upstroke. This improvement is larger in non-cyclists than in experienced cyclists but it can be optimized in the latter after a short-term training (2-4 weeks) with pedal force feedback or uncoupled cranks.

EVIDENCE SYNTHESIS

Despite that PULL enhances a lower muscular recruitment of contralateral knee extensors, GE and cycling performance variables are not significantly increased, probably due to the reversal effect of training with normal cranks and the highly robust pedaling technique of experienced cyclists. The question arises, as to whether or not, changes in pedaling technique can improve cycling efficiency if enough time is given for cyclists to adapt to a new pedaling technique.

CONCLUSIONS

Further studies should investigate the pedaling techniques in more "ecological" conditions, as there is not probably one but several pedaling techniques that could optimize cycling efficiency according to the pedaling conditions (time-trial, uphill, road, off-road and track cycling), and should also focus on the potential effects of long-term training of PULL pedaling technique on cycling efficiency and cycling performance.

On the biological mechanics and energetics of the hip joint muscle-tendon system assisted by passive hip exoskeleton

Passive exoskeletons have potential advantages in reducing metabolic energy cost. We consider a passive elastic exoskeleton (peEXO) providing hip flexion moment to assist hip flexors during walking, our goal is to use a biomechanical model to explore the biological mechanics and energetics of the hip joint muscle-tendon-exotendon system for obtaining the optimum stiffness of this peEXO at the muscle-level. Based on our developed hip musculoskeletal model capable of replicating human-like behaviors, the hip peEXO is firstly abstracted as a spring (i.e. exotendon), we then simulate the peEXO assisted human walking over a series of stiffnesses, the biological muscle-tendon dynamics is optimally solved by minimizing the total metabolic cost of muscles. The simulation results are consistent with the experimental data of walking with an exoskeleton prototype. We find peEXO of minor stiffness helps reducing the muscle force, activation, and metabolic energy cost of hip flexors, especially the iliopsoas; while stiffer peEXO causes extra metabolic energy cost of antagonist muscles especially the gluteus maximus. With an optimum rotational stiffness of 350 Nm rad^-1, the peEXO can reduce the metabolic energy cost of walking by ~7.1% and the hip joint muscles simultaneously have a 3% muscle efficiency promotion. The changes in muscle-tendon dynamics indicate it is more economical to assist the hip joint compared with the ankle joint, and periods of high muscle activation are ideal assistance phases for hip joint muscles. The modeling framework provides deep insights into the potential muscle-level mechanisms which are difficult to study via experiments alone, which is helpful to recover the mechanism of how energy cost is reduced under the external passive assistance and guide the design of passive hip EXOs.

The Role of Statins in Disease Modification and Cardiovascular Risk in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune, inflammatory disorder associated with excess cardiovascular morbidity and mortality. A complex interplay between traditional risk factors (dyslipidemia, insulin resistance, arterial hypertension, obesity, smoking) and chronic inflammation is implicated in the development of premature atherosclerosis and consequently in the higher incidence of cardiovascular events observed in RA patients. Despite the acknowledgment of elevated cardiovascular risk among RA individuals, its management remains suboptimal. While statin administration has a crucial role in primary and secondary cardiovascular disease prevention strategies as lipid modulating factors, there are limited data concerning the precise benefit of such therapy in patients with RA. Systemic inflammation and anti-inflammatory treatments influence lipid metabolism, leading to variable states of dyslipidemia in RA. Hence, the indications for statin therapy for cardiovascular prevention may differ between RA patients and the general population and the precise role of lipid lowering treatment in RA is yet to be established. Furthermore, some evidence supports a potential beneficial impact of statins on RA disease activity, attributable to their anti-inflammatory and immunomodulatory properties. This review discusses existing data on the efficacy of statins in reducing RA-related cardiovascular risk as well as their potential beneficial effects on disease activity.

Associations Between Practice-Related Changes in Motor Performance and Muscle Activity in Healthy Individuals: A Systematic Review

BACKGROUND

A well-learned motor skill is characterized by the efficient activation of muscles that are involved in movement execution. However, it is unclear if practice-related changes in motor performance correlate with those in quantitative markers of muscle activity and if so, whether the association is different with respect to the investigated muscle (i.e., agonist and antagonist) and quantitative myoelectric parameter. Thus, we conducted a systematic review and characterized associations between practice-related changes in motor performance and muscle activity in healthy individuals.

METHODS

A computerized systematic literature search was performed in the electronic databases PubMed, Web of Science, and SPORTDiscus up to September 2017 to capture all relevant articles. A systematic approach was applied to evaluate the 1670 articles identified for initial review. Studies were included only if they investigated healthy subjects aged 6 years and older and tested at least one measure of motor performance (e.g., error score, movement time) and quantitative muscle activity (i.e., amplitude domain: iEMG [integrated electromyography], RMS [root mean square]; time domain: duration of muscle activity, time to peak muscle activation). In total, 24 studies met the inclusionary criteria for review. The included studies were coded for the following criteria: age, learning task, practice modality, and investigated muscles (i.e., agonist and antagonist). Correlation coefficients for the relationship of motor performance changes with changes in electromyography (EMG) amplitude, and duration were extracted, transformed (i.e., Fisher's z-transformed r_z value), aggregated (i.e., weighted mean r_z value), and back-transformed to r values. To increase sample size, we additionally extracted pre and post practice data for motor performance and myoelectric variables and calculated percent change values as well as associations between both. Correlations were classified according to their magnitude (i.e., small r ≤ 0.69, medium r ≤ 0.89, large r ≥ 0.90).

RESULTS

Five studies reported correlation coefficients for the association between practice-related alterations in motor performance and EMG activity. We found small associations (range r = 0.015-0.50) of practice-related changes in motor performance with measures of agonist and antagonist EMG amplitude and duration. A secondary analysis (17 studies) that was based on the calculation of percent change values also revealed small correlations for changes in motor performance with agonist (r = - 0.25, 11 studies) and antagonist (r = - 0.24, 7 studies) EMG amplitude as well as agonist (r = 0.46, 8 studies) and antagonist (r = 0.29, 5 studies) EMG duration.

CONCLUSIONS

Our systematic review showed small-sized correlations between practice-related changes in motor performance and agonist and antagonist EMG amplitude and duration in healthy individuals. These findings indicate that practice-related changes can only partly be explained by quantitative myoelectric measures. Thus, future studies investigating biomechanical mechanisms of practice-related changes in motor performance should additionally include qualitative measures of muscle activity (e.g., timing of muscle activity, level of coactivation) and other biomechanical variables (i.e., kinetics, kinematics).

NF-κβ: A Potential Target in the Management of Vascular Complications of Diabetes

Diabetes is a metabolic disorder affecting large percentage of population worldwide. NF-κβ plays key role in pathogenesis of vascular complications of diabetes. Persistent hyperglycemia activates NF-κβ that triggers expression of various cytokines, chemokines and cell adhesion molecules. Over-expression of TNF-α, interleukins, TGF-β, Bcl2 and other pro-inflammatory proteins and pro-apoptotic genes by NF-κβ is key risk factor in vascular dysfunction. NF-κβ over-expression also triggers calcification of endothelial cells leading to endothelial dysfunction and further vascular complications. Inhibition of NF-κβ pro-inflammatory pathway is upcoming novel target for management of vascular complications of diabetes. Various natural and synthetic inhibitors of NF-κβ have been studied in management of diabetic complications. Recent preclinical and clinical studies validate NF-κβ as promising target in the management of vascular complications of diabetes.

Oliveira CN, de Lorena VMB, de Paiva-Cavalcanti M. The Equivocal Role of Th17 Cells and Neutrophils on Immunopathogenesis of Leishmaniasis

Advances in the understanding of leishmaniasis progression indicate that cellular interactions more complex than the Th1/Th2 paradigm define the course of infection. Th17 cells are a crucial modulator of adaptive immunity against Leishmania parasites acting mainly on neutrophil recruitment and playing a dual role at the site of infection. This review describes the roles of both these cell types in linking innate defense responses to the establishment of specific immunity. We focus on the Th17-neutrophil interaction as a crucial component of anti-Leishmania immunity, and the clinical evolution of cutaneous or visceral leishmaniasis. To date, information obtained through experimental models and patient evaluations suggests that the influence of the presence of interleukin (IL)-17 (the main cytokine produced by Th17 cells) and neutrophils during Leishmania infections is strictly dependent on the tissue (skin or liver/spleen) and parasite species. Also, the time at which neutrophils are recruited, and the persistence of IL-17 in the infection microenvironment, may also be significant. A clearer understanding of these interactions will enable better measurement of the influence of IL-17 and its regulators, and contribute to the identification of disease/resistance biomarkers.

High-Speed Cycling Intervention Improves Rate-Dependent Mobility in Older Adults

PURPOSE

The aim was to determine the feasibility of a 6-wk speed-based exercise program that could be used to initiate new exercise behaviors and to improve rapid movement in older adults approaching frailty.

METHODS

The intervention group included 14 older adults (3 males and 11 females; mean ± SD, age = 70 ± 7.6 yr, height = 1.6 ± 0.11 m, mass = 76.8 ± 12.0 kg, body mass index = 27.7 ± 4.7 kg·m). The control group included 12 older adults (6 males and 6 females; mean ± SD, age = 69.2 ± 6.9 yr, height = 1.7 ± 0.09 m, mass = 78.2 ± 10.9 kg, body mass index = 25.3 ± 2.7 kg·m). Subjects included active older adults, including regular exercisers, but none were engaged in sports or exercises with an emphasis on speed (e.g., cycling spin classes or tennis). Stationary recumbent cycling was selected to minimize fall risk, and low pedaling resistance reduced musculoskeletal and cardiovascular load. Two weekly 30-min exercise sessions consisted of interval training in which subjects pedaled at preferred cadence and performed ten 20-s fast cadence intervals separated by 40 s of active recovery at preferred cadence.

RESULTS

Significant group-time interactions (P < 0.05) supported a 2-s improvement in the timed up and go test and a 34% improvement in rapid isometric knee extension contractions in the exercise group but not in controls. Central neural adaptations are suggested because this lower extremity exercise program also elicited significant improvements in the untrained upper extremities of the exercise group (elbow extension rate of force development scaling factor and Nine-Hole Peg Test, P < 0.05).

CONCLUSION

These results demonstrate that a relatively low dose of speed-based exercise can improve neuromuscular function and tests of mobility in older adults. Such a program serves as a sensible precursor to subsequent, more vigorous training or as an adjunct to a program where a velocity emphasis is lacking.

Effectiveness of pedalling retraining in reducing bilateral pedal force asymmetries

Previous studies have been limited to describe asymmetries during pedalling and suggest possible repercussion on performance and/or injury risks. However, few studies have presented strategies to mitigate asymmetries. The purpose of this study was to assess the effectiveness of a pedalling retraining intervention to reduce bilateral pedal force asymmetries. Twenty cyclists were assessed and 10 enrolled in a pedalling retraining method receiving visual and verbal feedback of pedal forces. The asymmetry index was computed for comparison of bilateral peak pedal forces and used during retraining (12 trials at 70% of peak power). Significantly larger asymmetry was observed for asymmetrical cyclists at the first three trials (P < 0.01 and ES = 1.39), which was reduced when post-retraining was compared to measures from symmetrical cyclists (P = 0.69 and ES = 0.18). Cyclists with larger asymmetry (>20%) in bilateral pedal forces reduce their asymmetries using sessions of pedalling retraining and achieve asymmetry indices similar to symmetrical cyclists.

Quadriceps and hamstring muscle activity during cycling as measured with intramuscular electromyography

Purpose

The aim of this study was to describe thigh muscle activation during cycling using intramuscular electromyographic recordings of eight thigh muscles, including the biceps femoris short head (BFS) and the vastus intermedius (Vint).

Methods

Nine experienced cyclists performed an incremental test (start at 170 W and increased by 20 W every 2 min) on a bicycle ergometer either for a maximum of 20 min or to fatigue. Intramuscular electromyography (EMG) of eight muscles and kinematic data of the right lower limb were recorded during the last 20 s in the second workload (190 W). EMG data were normalized to the peak activity occurring during this workload. Statistical significance was assumed at p ≤ 0.05.

Results

The vastii showed a greater activation during the 1st quadrant compared to other quadrants. The rectus femoris (RF) showed a similar activation, but with two bursts in the 1st and 4th quadrants in three subjects. This behavior may be explained by the bi-articular function during the cycling movement. Both the BFS and Vint were activated longer than, but in synergy with their respective agonistic superficial muscles.

Conclusion

Intramuscular EMG was used to verify muscle activation during cycling. The activation pattern of deep muscles (Vint and BFS) could, therefore, be described and compared to that of the more superficial muscles. The complex coordination of quadriceps and hamstring muscles during cycling was described in detail.

Comparison of kinetics, kinematics, and electromyography during single-leg assisted and unassisted cycling

To use single-leg cycling training for varying populations, it is important to understand whether a counterweight attached to the contralateral crank during single-leg cycling drills replicates the effects of the opposite leg in the ipsilateral leg. Therefore, we compared single-leg assisted cycling using a counterweight on the contralateral crank for joint kinetics, kinematics, and lower-limb muscle activation. Fourteen healthy nonathletes performed 2 bilateral cycling trials (240 ± 23 W and 90 ± 2 rpm) and 2 single-leg trials (120 ± 11 W and 90 ± 2 rpm) for measurements of pedal force, joint kinematics, and muscle activation of their right lower limb. For 1 single-leg trial, a custom-made adaptor was used to attach 10 kg of weight to the contralateral leg. Total force applied on the pedal, pedal force effectiveness, the mean joint angles and range of motion, mechanical work at the crank, hip, knee, and ankle joints, electromyography, pedaling cadence, and right crank mechanical work were assessed. Biceps femoris (87%), vastus lateralis (15%), rectus femoris (57%), tibialis anterior (57%), and gastrocnemius medialis (12%) activations were larger in the single-leg assisted trial compared with the bilateral trial. Lower total pedal force (17%) and increased index of effectiveness (16%) also indicate mechanical differences in single-leg cycling using a counterweight on the contralateral crank than conventional bilateral cycling. Single-leg assisted training should be used with caution because of potential differences in muscle recruitment and pedaling kinetics compared with bilateral cycling.

How to assess performance in cycling: the multivariate nature of influencing factors and related indicators

Finding an optimum for the cycling performance is not a trivial matter, since the literature shows the presence of many controversial aspects. In order to quantify different levels of performance, several indexes have been defined and used in many studies, reflecting variations in physiological and biomechanical factors. In particular, indexes such as Gross Efficiency (GE), Net Efficiency (NE) and Delta Efficiency (DE) have been referred to changes in metabolic efficiency (Eff_Met), while the Indexes of Effectiveness (IE), defined over the complete crank revolution or over part of it, have been referred to variations in mechanical effectiveness (Eff_Mech). All these indicators quantify the variations of different factors [i.e., muscle fibers type distribution, pedaling cadence, setup of the bicycle frame, muscular fatigue (MFat), environmental variables, ergogenic aids, psychological traits (Psych_Tr)], which, moreover, show high mutual correlation. In the attempt of assessing cycling performance, most studies in the literature keep all these factors separated. This may bring to misleading results, leaving unanswered the question of how to improve cycling performance. This work provides an overview on the studies involving indexes and factors usually related to performance monitoring and assessment in cycling. In particular, in order to clarify all those aspects, the mutual interactions among these factors are highlighted, in view of a global performance assessment. Moreover, a proposal is presented advocating for a model-based approach that considers all factors mentioned in the survey, including the mutual interaction effects, for the definition of an objective function E representing the overall effectiveness of a training program in terms of both Eff_Met and Eff_Mech.

Effects of different pedalling techniques on muscle fatigue and mechanical efficiency during prolonged cycling

The present study aimed to test the influence of the pedalling technique on the occurrence of muscular fatigue and on the energetic demand during prolonged constant-load cycling exercise. Subjects performed two prolonged (45 min) cycling sessions at constant intensity (75% of maximal aerobic power). In a random order, participants cycled either with their preferred technique (PT) during one session or were helped by a visual force-feedback to modify their pedalling pattern during the other one (FB). Index of pedalling effectiveness was significantly (P<0.05) improved during FB (41.4 ± 5.5%); compared with PT (36.6 ± 4.1%). Prolonged cycling induced a significant reduction of maximal power output, which was greater after PT (-15 ± 9%) than after FB (-7 ± 12%). During steady-state FB, vastus lateralis muscle activity was significantly (P<0.05) reduced, whereas biceps femoris muscles activities increased compared with PT. Gross efficiency (GE) did not significantly differ between the two sessions, except during the first 15 min of exercise (FB: 19.0 ± 1.9% vs PT: 20.2 ± 1.9%). Although changes in muscular coordination pattern with feedback did not seem to influence GE, it could be mainly responsible for the reduction of muscle fatigue after prolonged cycling.