The validity of a single inertial sensor to assess cervical active range of motion.

Cervical active range of motion (AROM) is an important outcome measure for clinicians working with a range of patient populations, especially people with neck pain. Multi-sensor inertial measurement unit (IMU) devices demonstrate good validity in the research laboratory but are expensive and not easily accessible in clinical settings. The use of single-IMU devices has been proposed but their validity for measuring cervical AROM is unknown. A concurrent and content validity study was conducted, comparing accuracy of single-IMU NeckCare Pro™ with multi-IMU Xsens™ for measuring cervical AROM in healthy adults (8 males, 7 females, mean age 30.6 years [SD 10.4]). Cervical AROM was assessed for flexion, extension, rotation (right and left), and lateral flexion (right and left), whereby six repetitions were performed for each movement with the subjects strapped to a high-back chair. Regarding content validity, Xsens™ detected a small amount of thoracic movement that could not be detected by the NeckCare Pro™ during cervical AROM testing, with means ranging from 1.5° to 4.1°. However, this did not significantly impact concurrent validity, which was good for all movements (ICC 0.764 - 0.966). This paper found that single-IMU technology (NeckCare Pro™) had good validity for measuring cervical AROM in healthy adults when subjects were strapped to a chair to limit trunk movement.

Criterion validity of neural networks to assess lower limb motion during cycling.

The use of marker-less methods to automatically obtain kinematics of movement is expanding but validity to high-velocity tasks such as cycling with the presence of the bicycle on the field of view is needed when standard video footage is obtained. The purpose of this study was to assess if pre-trained neural networks are valid for calculations of lower limb joint kinematics during cycling. Motion of twenty-six cyclists pedalling on a cycle trainer was captured by a video camera capturing frames from the sagittal plane whilst reflective markers were attached to their lower limb. The marker-tracking method was compared to two established deep learning-based approaches (Microsoft Research Asia-MSRA and OpenPose) to estimate hip, knee and ankle joint angles. Poor to moderate agreement was found for both methods, with OpenPose differing from the criterion by 4-8° for the hip and knee joints. Larger errors were observed for the ankle joint (15-22°) but no significant differences between methods throughout the crank cycle when assessed using Statistical Parametric Mapping were observed for any of the joints. OpenPose presented stronger agreement with marker-tracking (criterion) than the MSRA for the hip and knee joints but resulted in poor agreement for the ankle joint.

Validity of Neural Networks to Determine Body Position on the Bicycle.

Purpose: With the increased access to neural networks trained to estimate body segments from images and videos, this study assessed the validity of some of these networks in enabling the assessment of body position on the bicycle. Methods: Fourteen cyclists pedaled stationarily in one session on their own bicycles while video was recorded from their sagittal plane. Reflective markers attached to key bony landmarks were used to manually digitize joint angles at two positions of the crank (3 o'clock and 6 o'clock) extracted from the videos (Reference method). These angles were compared to measurements taken from videos generated by two deep learning-based approaches designed to automatically estimate human joints (Microsoft Research Asia-MSRA and OpenPose). Results: Mean bias for OpenPose ranged between 0.03° and 1.81°, while the MSRA method presented errors between 2.29° and 12.15°. Correlation coefficients were stronger for OpenPose than for the MSRA method in relation to the Reference method for the torso (r = 0.94 vs. 0.92), hip (r = 0.69 vs. 0.60), knee (r = 0.80 vs. 0.71), and ankle (r = 0.23 vs. 0.20). Conclusion: OpenPose presented better accuracy than the MSRA method in determining body position on the bicycle, but both methods seem comparable in assessing implications from changes in bicycle configuration.

Caffeine mouth rinse enhances performance, fatigue tolerance and reduces muscle activity during moderate-intensity cycling.

We investigated the effects of caffeine mouth rinse on endurance performance, muscle recruitment (i.e., electromyographic activity of the vastus lateralis and rectus femoris), rating of perceived effort and heart rate. Twelve physically-active healthy men cycled at 80% of their respiratory compensation point until task failure. The participants rinsed their mouths for 10 seconds with placebo (PLA, 25 mL of a solution composed of non-caloric mint essence) or caffeine (CAF, 25 mL of 1.2% of anhydrous caffeine concentration with non-caloric mint essence) every 15 minutes of exercise. Time until exhaustion increased 17% (effect size = 0.70) in CAF compared to PLA (p = 0.04). The wavebands of low-frequency electromyographic activity (EMG) of the vastus lateralis and rectus femoris was lower in CAF group than PLA at 50% of the time until exhaustion (p = 0.04). The global EMG signal was lower in CAF group than PLA at 100% of the time until exhaustion (p = 0.001). The rating of perceived effort pooled was higher in CAF mouth rinse (p = 0.001) than PLA group. No effect was found on the heart rate between the groups (p > 0.05). Caffeine mouth rinse increases endurance performance, rating of perceived effort and decreases muscle activity during a moderate-intensity exercise.

Comparison of linea alba length and core-muscles engagement during core and lower back orientated exercises.

BACKGROUND: A comparison of Linea Alba (LA) length and engagement of the Transverse Abdominis (TrA), External Oblique (EO) and Internal Oblique (IO) between core-orientated and lower back orientated exercises (e.g. glute bridge and hip extension) is lacking. Therefore, the aim of this study was to compare the length of the LA and the engagement of TrA, EO and IO when performing the prone plank, bird dog, dead bug, lateral plank, glute bridge and hip extension. METHODS: Thirteen apparently healthy participants volunteered to this study. Ultrasound scanning of the anterior and antero-lateral abdominal walls at baseline and whilst performing prone plank, bird dog, dead bug, lateral plank, glute bridge and hip extension exercises was performed. LA length and thickness of the TrA, EO and IO were measured from ultrasound images. RESULTS: LA length (p = 0.77) and TrA thickness (p = 0.23) were not different between exercises. EO thickness was larger for the lateral plank compared to the bird dog (p = 0.01, d = 1.73), glute bridge (p < 0.01, d = 2.64), and hip extension (p < 0.01, d = 1.89). The dead bug was also larger in comparison to the glute bridge (p < 0.01, d = 2.05) and to the hip extension (p = 0.01, d = 1.45). For the IO thickness, the lateral plank was larger than the bird dog (p = 0.03, d = 1.21) and the dead bug (p = 0.04, d = 1.12). CONCLUSION: No difference was observed between exercises for the length of the LA or for the thickness of the TrA, which suggests that this muscle is similarly engaged in the assessed exercises, leading to a consistent stretch for the LA.

Effects from loaded walking with polyurethane and styrene-butadiene rubber midsole military boots on kinematics and external forces: A statistical parametric mapping analysis.

This study compared ground reaction forces (GRF) and lower limb two-dimensional (2D) kinematic waveforms, with and without load carriage, in military personnel walking in two different types of boots. Data were measured in 24-soldiers walking on a 10-m walkway under four randomized crossover trials: wearing two military boots (styrene-butadiene rubber midsole - SBR - 63 Shore A; and polyurethane midsole - PU - 48 Shore A); with and without a 15-kg backpack. GRF traditional parameters were evaluated by two-way ANOVAs. GRF and kinematic waveforms were assessed using a statistical parametric mapping (SPM) method (two-way ANOVA). No interaction effects were observed between footwear and load. GRF at the beginning of stance was lower while wearing the SBR boot condition compared to the PU boot condition. Load carriage increased trunk, hip, and knee flexion. The analyzed military boots did not affect movement patterns during loaded walking and the military boot with SBR midsole material reduced impact to a greater extent. The study demonstrated that the design and materials (e.g., midsole material and thickness) used in boot manufacturing can influence military boot performance.

Effects of exercise mode in knee cartilage thickness.

BACKGROUND: It is unclear how cycling and running would differ in terms of changes in cartilage thickness. Also, given squats are a popular type of exercise used to strengthen lower limbs, it is critical to assess if loads used during resisted training could lead to changes in cartilage cushioning properties. Therefore, the purpose of this study was to compare the effects of exercise mode in knee cartilage thickness. METHODS: This study utilized a randomized cross-over design with repeated measures. All sessions were completed between 48hrs and seven days, at the same time of the day. Fourteen (seven males and seven females) apparently healthy participants without musculoskeletal or neurological diseases volunteered for the study. Participants were assessed after squats and functional exercises (n = 18 knees) or after running and cycling (n = 10 knees). All ultrasound images were collected at participants' arrival in the laboratory (Baseline), after warm-up (Pre-exercise), after the completion of each exercise protocol (Post-exercise), and at five (5-min) and 10 minutes (10-min) after exercise. RESULTS: Cartilage thickness did not change after squats performed with 60% of 1-RM or after a set of three functional exercises (i.e. sit-to-stand, lunges, and step-ups; p = 0.68). However, longer duration exercises (i.e. cycling and running) led to increases in cartilage thickness after 5-min from the completion of the exercise (p = 0.02). CONCLUSION: Knee cartilage may have capacity to sustain short-term cyclical loads applied during exercise (i.e. squats and functional exercises) but not to moderate duration exercises (i.e. cycling and running).

Corrigendum: Triceps Surae Muscle Architecture Adaptations to Eccentric Training.

[This corrects the article DOI: 10.3389/fphys.2019.01456.].

Physiological and biomechanical comparison between electrically assisted bicycles and motorbikes during simulated mail delivery.

Electrically assisted bicycles (EABs) and motorbikes were compared in terms of energy expenditure, internal and external forces, and technique when delivering mail with different loads at different distances from the mailbox. Twenty-two postal workers performed two simulated postal tasks (foot placement [close vs. far] and delivery, and simulated mail delivery circuit) while carrying 0 and 32 kg. Independent of mail load, delivering mail with EABs was classified as moderate intensity and resulted in 33% higher energy expenditure when compared to motorbikes. Ground reaction forces were larger (7-25%) for EAB when compared to motorbike. Larger ground reaction forces were observed when both EABs and motorbikes were positioned further from the mailbox (5-23%). Using EABs during mail delivery has potential to result in numerous health benefits that are associated with moderate intensity physical activity, but can lead to larger external forces when compared to motorbikes. Practitioner summary: In order to compare electrically assisted bicycles (EAB) and motorbikes, postal workers performed simulated deliveries in the laboratory whilst measurements of energy expenditure, body loads and movement patters were undertaken. Body loads and energy expenditure were larger using EAB, which result in health benefits associated with moderate intensity exercise. Abbreviations: EAB: electrically assisted bicycles; CI: confidence interval; UHEC: University Human Ethics Committee; MB: motorbike;SH: seat height; SF: seat to floor distance; VO2: oxygen uptake; VCO2: exhaled carbon dioxide; RER: respiratory exchangeratio; TTL signal: Transistor-Transistor Logic; MET: metabolic equivalent; 3D: three-dimensional; IIR: infinite impulse response; Hz:Hertz; N: Newtons; ROM: range of motion; SD: standard deviation; p: significance level; d: Cohen effect sizes.

Triceps Surae Muscle Architecture Adaptations to Eccentric Training.

BACKGROUND: Eccentric exercises have been used in physical training, injury prevention, and rehabilitation programs. The systematic use of eccentric training promotes specific morphological adaptations on skeletal muscles. However, synergistic muscles, such as the triceps surae components, might display different structural adaptations due to differences in architecture, function, and load sharing. Therefore, the purpose of this study was to determine the effects of an eccentric training program on the triceps surae (GM, gastrocnemius medialis; GL, gastrocnemius lateralis; and SO, soleus) muscle architecture. METHODS: Twenty healthy male subjects (26 ± 4 years) underwent a 4-week control period followed by a 12-week eccentric training program. Muscle architecture [fascicle length (FL), pennation angle (PA), and muscle thickness (MT)] of GM, GL, and SO was evaluated every 4 weeks by ultrasonography. RESULTS: Fascicle lengths (GM: 13.2%; GL: 8.8%; SO: 21%) and ML increased (GM: 14.9%; GL: 15.3%; SO: 19.1%) from pre- to post-training, whereas PAs remained similar. GM and SO FL and MT increased up to the 8th training week, whereas GL, FL increased up to the 4th week. SO displayed the highest, and GL the smallest gains in FL post-training. CONCLUSION: All three synergistic plantar flexor muscles increased FL and MT with eccentric training. MT increased similarly among the synergistic muscles, while the muscle with the shortest FL at baseline (SO) showed the greatest increase in FL.

Muscle force adaptation to changes in upper body position during seated sprint cycling.

Sprint cycling performance depends upon the balance between muscle and drag forces. This study assessed the influence of upper body position on muscle forces and aerodynamics during seated sprint cycling. Thirteen competitive cyclists attended two sessions. The first session was used to determine handlebar positions to achieve pre-determined hip flexion angles (70-110° in 10° increments) using dynamic bicycle fitting. In the second session, full body kinematics and pedal forces were recorded throughout 2x6-s seated sprints at the pre-determined handlebar positions, and frontal plane images were used to determine the projected frontal area. Leg work, joint work, muscle forces and frontal area were compared at three upper body positions, being optimum (maximum leg work), optimal+10° and optimal-10° of hip flexion. Larger hip (p = 0.01-0.02) and reduced knee (p = 0.02-0.03) contribution to leg work were observed at the optimal+10° position without changes at the ankle joint (p = 0.39). No differences were observed in peak muscle forces across the three body positions (p = 0.06-0.48). Frontal area was reduced at optimum+10° of hip flexion when compared to optimum (p = 0.02) and optimum-10° (p < 0.01). These findings suggest that large changes in upper body position can influence aerodynamics and alter contributions from the knee and hip joints, without influencing peak muscle forces.

Time course of neuromechanical and morphological adaptations to triceps surae isokinetic eccentric training.

OBJECTIVES: To document the magnitude and the time course of neuromechanical and morphological adaptations in response to a triceps surae eccentric training program. METHODS: Twenty healthy male subjects completed a control period followed by a 12-week isokinetic eccentric training program. Triceps surae neuromechanical and morphological evaluations were performed every 4 weeks. RESULTS: The training program led to increases in: eccentric (32%), isometric (13%) and concentric (20%) torques; eccentric (32%) and isometric (24%) electromyographic activity; and, muscle thickness (14%). Torque and muscle thickness increased until the 8th training week. Eccentric and isometric activation increased until the 4th training week. No change was found in concentric activation. The angles of peak torque in eccentric and concentric tests shifted towards longer muscle lengths. While eccentric and isometric strength gains are explained by increased neural activation and muscle mass, changes in concentric torque are not related to neural effects. CONCLUSIONS: Eccentric training led to increases in maximum eccentric and isometric force production due to adaptations in muscle activation and muscle mass. Among the advantages of the shift in the optimal length for force production towards longer lengths, are the increased total joint range of motion and a lower predisposition for muscle strain injuries.

Potential factors associated with knee pain in cyclists: a systematic review.

The potential factors associated with overuse injuries and pain in cyclists that are supported by evidence remain unclear. Our study aimed at assessing, using a systematic search of the most updated evidence, the main factors related to overuse knee-related pain and/or injuries in cyclists. The search assessed any potential mechanism related to knee pain or injury that could be used in the clinical practice. Databases were searched (i.e., PubMed, Scopus, Web of Science, and EBSCO). Studies were included if they presented results from original studies. They had to include, preferably but not limited to, recreational and/or competitive cyclists with or without knee pain. Quality of articles was assessed. Eleven articles were deemed eligible for full text appraisal. Studies involved generally the assessment of biomechanical outcomes associated with knee pain in cyclists. Overall, studies showed that cyclists with knee pain present larger knee adduction and larger ankle dorsiflexion and differences in activation for hamstrings and quadriceps muscles. Unclear results were observed for knee moments and no differences were observed for knee flexion angle, tibiofemoral and patellofemoral forces. It is important to state that varied types of knee pain were mixed in most studies, with 2 focused on anterior-related pain. Cyclists with overuse-related pain or injuries on their knees presented an increased medial projection of their knees and an altered activation of the Vastus Medialis and Vastus Lateralis muscles. However, this limited evidence is based on retrospective studies comparing cyclists with and without pain, which limits the conclusion on how cyclists develop knee pain and what are the main options for treatment of knee pain.

Effects of high loading by eccentric triceps surae training on Achilles tendon properties in humans.

PURPOSE: To document the magnitude and time course of human Achilles tendon adaptations (i.e. changes in tendon morphological and mechanical properties) during a 12-week high-load plantar flexion training program. METHODS: Ultrasound was used to determine Achilles tendon cross-sectional area (CSA), length and elongation as a function of plantar flexion torque during voluntary plantar flexion. Tendon force-elongation and stress-strain relationships were determined before the start of training (pre-training) and after 4 (post-4), 8 (post-8) and 12 (post-12) training weeks. RESULTS: At the end of the training program, maximum isometric force had increased by 49% and tendon CSA by 17%, but tendon length, maximal tendon elongation and maximal strain were unchanged. Hence, tendon stiffness had increased by 82%, and so had Young's modulus, by 86%. Significant changes were first detected at post-4 in stiffness (51% increase) and Young's modulus (87% increase), and at post-8 in CSA (15% increase). CONCLUSIONS: Achilles tendon material properties already improved after 4 weeks of high-load training: stiffness increased while CSA remained unchanged. Tendon hypertrophy (increased CSA) was observed after 8 training weeks and contributed to a further increase in Achilles tendon stiffness, but tendon stiffness increases were mostly caused by adaptations in tissue properties.

Reproducibility of upper leg EMG frequency content during cycling.

Reproducibility of frequency content from surface electromyography (sEMG) signals has not been assessed and it is unknown if incremental load testing design could affect sEMG in cycling. The goals of this study were to assess the reproducibility of measures from sEMG frequency content between sessions and to compare these frequency components between a ramp and a step incremental cycling test. Eighteen cyclists performed four incremental load cycling tests to exhaustion. Two tests were performed using a step increment (load started at 100 W for 3 min followed by increments of 30 W every 3 min) and two were performed using a ramp increment (load started at 100 W for 1 min followed by increments of 30 W·min-1). sEMG was monitored bilaterally for the rectus femoris and vastus lateralis throughout the tests and converted into overall activation (whole signal bandwidth), high- and low-frequency contents. The reproducibility of the frequency content ranged from none to strong (ICC = 0.07-0.90). Vastus lateralis activation was larger at the step compared to the ramp test (P < 0.01), without differences for rectus femoris (P = 0.22-0.91) and for the high-frequency (P = 0.28-0.95) and low-frequency contents (P = 0.13-0.94). sEMG from vastus lateralis and rectus femoris presented none to strong reproducibility. Vastus lateralis is more activated in step test design.

Neuromuscular fatigue is weakly associated with perception of fatigue and function in patients with rheumatoid arthritis.

To assess electromyographic parameters of neuromuscular fatigue in knee extensors and their association with clinical, functional and emotional features in patients with rheumatoid arthritis (RA). Thirty-eight female patients with RA participated. Electromyography parameters (changes in signal amplitude, represented by the root mean square, and frequency content, represented by median frequency-MDF) were assessed during a submaximal (60%) isometric contraction of the knee extensors, sustained for 60 s. Clinical characteristics; the 28-joint Disease Activity Score (DAS-28) in which includes count of swollen joints (out of the 28) and tender joints (out of the 28), the erythrocyte sedimentation rate and global disease activity measured on a visual analogue scale; serum C reactive protein (CRP); information on treatment; the Health Assessment Questionnaire; the Functional Assessment of Chronic Illness Therapy fatigue scale (FACIT-F); the Short Form Health Survey (SF-36) and the International Physical Activity Questionnaire (IPAQ), were also assessed. The mean patient age was 51.0 ± 8.2 years, mean disease activity score was 11.5 ± 7.1, and mean CRP level was 8.0 ± 7.8 mg/dL. There was a moderate correlation between MDF and age (r = 0.5), as well as weak correlations of MDF with FACIT-F (r = 0.3), physical functioning (r = - 0.3) and vitality domains (r = - 0.3) of the SF-36, and IPAQ (r = - 0.3) (p ≤ 0.05 for all). No association was observed between electromyography measurements and clinical or treatment features. The electromyographic parameter MDF was correlated with perception of fatigue, age, physical functioning and vitality domains of SF-36, and physical activity level in this sample. These results indicate that primary muscle factors should also be considered when managing perceived fatigue in patients with RA.

Patellofemoral and tibiofemoral forces during knee extension: simulations to strength training and rehabilitation exercises / Forças nas articulações tibiofemoral e patelofemoral durante a extensão dos joelhos: simulações aplicadas ao treino de força e à reabilitação

Abstract Introduction: Limited evidence has been shown on ways to optimize the mechanical design of machines in order to minimize knee loads. Objective: This study compared six computer simulated models of open kinetic knee extension exercises for patellofemoral pressure and tibiofemoral forces. Methods: A musculoskeletal model of the lower limb was developed using six different cam radius to change resistive forces. A default machine, a constant cam radius, a torque-angle model, a free-weight model and two optimized models were simulated. Optimized models reduced cam radius at target knee flexion angles to minimize knee forces. Cam radius, human force, tibiofemoral compressive and shear force, and patellofemoral pressure were compared for the six models using data from five knee flexion angles. Results: Large reductions in cam radius comparing the free-weight model to other models (73-180%) were limited to the large human force for the constant cam model to other models (9-36%). Larger human force (13 -36%) was estimated to perform knee extension using a constant cam radius compared other models without large effects in knee joint forces. Conclusion: Changes in cam design effected human without a potential impact in knee loads.

Resumo Introdução: As evidências são limitadas quanto às formas de otimização do arranjo mecânico das máquinas a fim de minimizar as forças na articulação do joelho. Objetivo: O presente estudo comparou seis modelos de extensão de joelhos realizados em cadeia cinética aberta sob a pressão aplicada nas articulações patelofemoral e tibiofemoral. Métodos: Um modelo do sistema musculo-esquelético do membro inferior foi desenvolvido utilizando seis desenhos de roldana com o objetivo de alterar as forças resistivas. Uma máquina referência foi utilizada, uma com uma roldana concêntrica, um modelo baseado na relação torque-ângulo dos extensores do joelho, um modelo de peso livre e dois modelos otimizando a aplicação de cargas foram simulados. A otimização foi aplicada visando reduzir o raio da roldana excêntrica e minimizar as forças aplicadas no joelho. O raio da roldana, a força produzida pelo executante, as forças compressivas e de cisalhamento nas articulações tibiofemoral e a pressão na articulação patelofemoral foram comparadas para os seis modelos de máquina utilizando cinco ângulos de flexão do joelho. Resultados: Reduções no raio da roldana foram observadas comparando o modelo de peso livre com os demais modelos (73-180%). Maior força produzida foi observada para o modelo de roldana constante comparado aos demais modelos (9-36%). Maior força produzida foi estimada para realizar a extensão do joelho utilizando a roldana constante comparada com os demais modelos (13-36%) sem efeitos sobre as forças no joelho. Conclusão: O arranjo mecânico das máquinas alterou a força produzida pelo executante sem afetar as forças aplicadas no joelho.

Implicações da cadência de pedalada sobre a potência mecânica e o período de contração muscular no ciclismo / Pedaling cadence effects on mechanical power and muscle contraction timing during cycling

A energia mecânica necessária para a pedalada no ciclismo depende de ações musculares concêntricas e excêntricas. Contudo, até o momento não se tem conhecimento de como variações na cadência de pedalada podem influenciar o tipo de ação muscular utilizada. O presente estudo investigou os efeitos de alterações na cadência nas ações musculares concêntricas e excêntricas durante a pedalada. A absorção e a produção de potência pelas articulações foram calculadas para monitorar possíveis repercussões das mudanças na cadência sobre a cinética articular. Vinte e um ciclistas participaram do estudo (VO2pico: 64,1 ± 5.0 ml/kg/min; volume de treinamento: 368,2 ± 69,5 km/semana). Na primeira sessão de avaliação, a potência máxima (POMAX) e a potência produzida relativa ao segundo limiar ventilatório (POLV2) foram determinadas durante teste incremental até a exaustão. Na segunda sessão, os ciclistas realizaram dois testes de dois minutos de duração a 70 e 90 rpm e carga constante (POLV2). A ativação de seis músculos, a força aplicada no pedal e a cinemática do membro inferior direito foram avaliadas. Um maior tempo de ativação foi observado em fase excêntrica para os músculos vasto medial (8%; p < 0,01) e bíceps femoral (20%; p = 0,04) a 70 rpm em relação a 90 rpm, além de maior tempo de ativação em fase concêntrica para o músculo vasto medial (10%; p = 0,04) a 90 rpm em relação a 70 rpm. Não se observou diferença nas potências articulares entre as cadências testadas. A não alteração da potência articular sugere uma tendência de conservação do padrão do movimento com a alteração da cadência de pedalada. A ativação excêntrica de músculos da articulação do joelho pode estar relacionada com o controle articular, transmissão de força e redução do custo energético

The mechanical energy required to propel the crank may depend on eccentric and concentric muscle actions. However, it is uncertain whether pedaling cadence would elicit changes in concentric and eccentric contributions. Therefore, the purpose of the present study was to investigate the effects of alterations in pedaling cadence on the eccentric and concentric muscle actions. Joint power production and absorption were calculated to assess potential effects from variations in pedaling cadence on joint kinetics. Twenty-one cyclists participated in this study (VO2pico: 64.1 ± 5.0 ml/kg/min; training volume: 368.2 ± 69.5 km/week). In their first session, maximal power output (POMAX) and power output related to the second ventilation threshold (POVT2) were determined during an incremental maximal cycling test to exhaustion. In their second session, cyclists performed two 2-min trials with workload from their POVT2 at two different cadences (70 and 90 rpm). Muscle activation of six muscles, pedal forces and lower limb joint kinematics were evaluated. Longer eccentric contraction at 70 rpm for vastus medialis (8%; p < 0.01) and biceps femoris (20%; p = 0.04) were observed compared to 90 rpm. Longer concentric contraction for vastus medialis muscle (10%; p = 0.04) at 90 rpm was observed compared to 70 rpm. There were no differences in joint power production and absorption among pedaling cadences. No alterations in joint power could indicate maintenance of movement when pedaling cadence is changed. Eccentric contractions from knee muscles could be related to joint control, force transmission and reduced energy cost

Saddle height effects on pedal forces, joint mechanical work and kinematics of cyclists and triathletes.

The effects of saddle height on pedal forces and joint kinetics (e.g. mechanical work) are unclear. Therefore, we assessed the effects of saddle height on pedal forces, joint mechanical work and kinematics in 12 cyclists and 12 triathletes. Four sub-maximal 2-min cycling trials (3.4 W/kg and 90 rpm) were conducted using preferred, low and high saddle heights (±10° knee flexion at 6 o'clock crank position from the individual preferred height) and an advocated optimal saddle height (25° knee flexion at 6 o'clock crank position). Right pedal forces and lower limb kinematics were compared using effect sizes (ES). Increases in saddle height (5% of preferred height, ES=4.6) resulted in large increases in index of effectiveness (7%, ES=1.2) at the optimal compared to the preferred saddle height for cyclists. Greater knee (11-15%, ES=1.6) and smaller hip (6-8%, ES=1.7) angles were observed at the low (cyclists and triathletes) and preferred (triathletes only) saddle heights compared to high and optimal saddle heights. Smaller hip angle (5%, ES=1.0) and greater hip range of motion (9%, ES=1.0) were observed at the preferred saddle height for triathletes compared to cyclists. Changes in saddle height up to 5% of preferred saddle height for cyclists and 7% for triathletes affected hip and knee angles but not joint mechanical work. Cyclists and triathletes would opt for saddle heights <5 and <7%, respectively, within a range of their existing saddle height.