Biomechanical Examination of Wrist Flexors and Extensors with Biodex System Dynamometer-Isometric, Isokinetic and Isotonic Protocol Options.

Background and Objectives: Biodex System® is an advanced dynamometer used for testing various biomechanical parameters of muscles. Test outcomes allow for the identification of muscle pathology and consequently lead to a clinical diagnosis. Despite being widely used for the testing and rehabilitation of the human musculoskeletal system, no universal and acceptable protocol for wrist examination has been proposed for patients with wrist pathology. In this study, the authors aim to identify the most appropriate protocol for testing the biomechanical parameters of flexors and extensors of the wrist. Materials and Methods: A group of 20 patients with symptomatic tennis elbow and 26 healthy volunteers were examined using three different protocols: isokinetic, isometric and isotonic. Protocol order for each study participant was assigned at random with a minimum of a 24 h break between protocols. All protocol parameters were set according to data obtained from a literature review and an earlier pilot study. Following completion of each protocol, participants filled out a questionnaire-based protocol, assessing pain intensity during the exam, difficulty with exam performance and post-exam muscle fatigue. Results: The isotonic protocol showed the best patient tolerance and the highest questionnaire score. There was a significant difference (p < 0.05) between the three protocols in average pain intensity reported by study participants. All participants completed the isotonic protocol, but not all patients with symptomatic tennis elbow were able to complete the isometric and isokinetic protocols. The isotonic protocol was deemed "difficult but possible to complete" by study participants. Conclusions: The isotonic protocol is most suitable for testing the flexors and extensors of the wrist. It gives the most biomechanical data of all protocols, is well tolerated by patients and rarely causes pain during examination even in symptomatic participants.

Influence of stimulation frequency on early and late phase rate of torque and velocity development.

The early (≤50 ms) rate of torque development (RTD) is dependent upon the speed of neuromuscular activation; however, few studies have evaluated the determinants of rate of velocity development (RVD), which may be load-dependent. The purpose here was to explore the relationship between stimulation frequency with the early and late (≥100 ms) phase isometric RTD and isotonic RVD. The knee extensors of 16 (five female) young recreationally active participants were stimulated using 14 frequencies from 1 to 100 Hz during isometric and isotonic ("unloaded" and 7.5% of the isometric maximal voluntary contraction [MVC]) contractions. Isometric RTD and isotonic RVD were evaluated for the early (0-50 ms) and late (0-100 ms) phases from torque and velocity onset, respectively. Sigmoid functions were fit and bilinear regressions were used to examine the slopes of the steep portion of the curve and the plateau frequency. RTD- and RVD-frequency relationships were well described by a sigmoid function (all r2 > 0.96). Compared with the late phase, early isometric RTD, and unloaded RVD displayed lower slopes (all P ≤ 0.001) and higher plateau frequencies (all P < 0.001). In contrast, early and late RVD of a moderately loaded isotonic contraction did not display different slopes (P = 0.055) or plateau frequencies (P = 0.690). Early isometric RTD and unloaded isotonic RVD are more dependent on changes in stimulation frequency compared with late phases. However, RVD for a moderately loaded isotonic contraction displayed similar responses for the early and late phases. Therefore, a high frequency of activation is critical for early torque and velocity generation but dependent upon the load for isotonic contractions.NEW & NOTEWORTHY We show that during an "unloaded" isotonic contraction, the early phase rate of velocity development is more dependent upon a high electrical activation frequency compared with the late phase, similar to isometric torque. However, early and late phase rates of velocity development of moderately loaded isotonic contractions display similar responses. These results indicate that the determinants of isotonic shortening function are dependent on the externally applied load, highlighting the importance of task-specificity of contraction.

Differential effects of stimulation frequency on isometric and concentric isotonic contractile function in human quadriceps.

Electrically evoked contractions are used to assess the relationship between frequency input and contractile output to characterize inherent muscle function, and these have been done mostly with isometric contractions (i.e., no joint rotation). The purpose was to compare the electrically stimulated frequency and contractile function relationship during isometric (i.e., torque) with isotonic (i.e., concentric torque, angular velocity, and mechanical power) contractions. The knee extensors of 16 (5 female) young recreationally active participants were stimulated (∼1-2.5 s) at 14 frequencies from 1 to 100 Hz. This was done during four conditions, which were isometric and isotonic at loads of 0 (unloaded), 7.5%, and 15% isometric maximal voluntary contraction (MVC), and repeated on separate days. Comparisons across contractile parameters were made as a % of 100 Hz. Independent of the load, the mechanical power-frequency relationship was rightward shifted compared with isometric torque-frequency, concentric torque-frequency, and velocity-frequency relationships (all P ≤ 0.04). With increasing load (0%-15% MVC), the isotonic concentric torque-frequency relationship was shifted leftward systematically from 15 to 30 Hz (all P ≤ 0.04). Conversely, the same changes in load caused a rightward shift in the velocity-frequency relationship from 1 to 40 Hz (all P ≤ 0.03). Velocity was leftward shifted of concentric torque in the unloaded isotonic condition from 10 to 25 Hz (all P ≤ 0.03), but concentric torque was leftward shifted of velocity at 15% MVC isotonic condition from 10 to 50 Hz (all P ≤ 0.03). Therefore, isometric torque is not a surrogate to evaluate dynamic contractile function. Interpretations of evoked contractile function differ depending on contraction type, load, and frequency, which should be considered relative to the specific task.NEW & NOTEWORTHY In whole human muscle, we showed that the electrically stimulated power-frequency relationship was rightward shifted of the stimulated isometric torque-frequency relationship independent of isotonic load, indicating that higher stimulation frequencies are needed to achieve tetanus. Therefore, interpretations of evoked contractile function differ depending on contraction type (isometric vs. dynamic), load, and frequency. And thus, isometric measures may not be appropriate as a surrogate assessment when evaluating dynamic isotonic contractile function.

Voluntary activation of human knee extensors during isotonic shortening contractions.

PURPOSE: The interpolated twitch technique (ITT) is often used to assess voluntary activation during isometric contractions; however, this may have limited relevance to dynamic contractions. Although the ITT has been applied to relatively slow isokinetic contractions (< 150°/s), it has received limited consideration during unconstrained velocity (i.e., isotonic) contractions, despite their relevance to natural movements. Here, we explored the ITT during isotonic knee extension contractions using a modified dynamometer. METHODS: Young males (n = 6) and females (n = 4) performed isometric and isotonic knee extension contractions of sub-maximal and maximal intensities with doublet (150 Hz) muscle belly stimulations to assess voluntary activation. Following each voluntary isotonic contraction (velocity range ~ 35°/s to ~ 275°/s), resting potentiated doublets were evaluated during passive joint rotation at the same angular velocity achieved during voluntary efforts, to account for force-velocity characteristics. Correlations between voluntary activation and the proportion of maximal torque or power were evaluated for isometric and isotonic contractions, respectively. RESULTS: Isometric voluntary activation was strongly correlated with increasing torque output (r = 0.96, p < 0.001). Doublet torque during passive joint rotation displayed a hyperbolic relationship with increasing angular velocity (r = 0.98, p < 0.001). Isotonic voluntary activation was strongly correlated with increasing power output (r = 0.89, p < 0.001). During maximal effort contractions, no differences were observed in voluntary activation between isometric and isotonic conditions (89.4% vs. 89.2%, p = 0.904). CONCLUSIONS: The ITT is a valid approach to evaluate voluntary activation during an isotonic contraction using a modified dynamometer. Participants were able to achieve a similar high level of voluntary activation during isometric and isotonic contractions.

Three-Dimensional Ankle Exercise with Combined Isotonic Technique for an Obese Subject with Plantar Fasciitis: A Case Study.

Background and objectives: Obese people have many foot-related disorders and plantar fasciitis (PF) is the most common disorder among them. However, research on the role of therapeutic exercises in PF is lacking and there is no evidence to suggest its benefits. As such, a further insight into therapeutic exercises is needed within this group. This case study investigated the effect of three-dimensional (3D) ankle exercises using a combined isotonic (CI) technique on function and balance in an obese subject with PF. Material and methods: The subject in this study was a 28-year-old obese woman who was diagnosed with PF by an orthopedic surgeon. A 3D ankle exercise program was commenced three times a week for 15 min over 4 weeks. The evaluations were conducted at five intervals: pre-test, and at 1, 2, 3 and 4 weeks from the initiation of the intervention. The tests were conducted in the following order: the patient-specific functional scale test (PSFS), an ultrasound of the plantar fascia, the heel pressure and balance test, the pressure pain threshold (PPT), and the 4-way ankle strength test. Results: The mean score of the PSFS test reduced by 70.55% after 4 weeks of the intervention. The thickness of the plantar fascia and heel pressure measured during single-leg standing decreased by 6.67% and 10.37%, respectively, after 4 weeks of the intervention. The anteroposterior and medial-lateral balance ability showed improvements of 8.29% and 8.61%, respectively, after 4 weeks of the intervention. The PPT improved by 38.01% after 4 weeks of the intervention. In the 4-way ankle strength test, dorsiflexion, plantar flexion, inversion, and eversion increased by 14.46%, 9.63%, 4.3% and 13.25%, respectively, after 4 weeks of the intervention. Conclusion: 3D ankle exercises utilizing the CI technique were shown to be effective in improving foot function, pressure pain, and muscle strength in dorsiflexion and inversion in an obese patient with PF.

Evaluación de la función muscular del cuádriceps en pacientes con EPOC modera-severa / Evaluation of quadricep muscle function in patients with moderate-severe COPD

Objetivo: el objetivo del estudio fue evaluar la función muscular periférica de pacientes con EPOC moderadasevera, mediante la medición de la fuerza muscular isométrica e isotónica del cuádriceps y la masa muscular mediante ecografía. Método: fueron incluidos pacientes con EPOC moderada-severa estables, remitidos a Rehabilitación Respiratoria. En la extremidad dominante, se midió la fuerza isométrica (dinamómetro hidráulico), test 1RM y se realizó una ecografía para obtener el área transversal y dimensiones de diversas secciones musculares. Resultados: participaron 34 pacientes con EPOC estable: GOLD 2 (n = 11), GOLD 3 (n = 12) y GOLD 4 (n = 11) Los GOLD 4 tenían un IMC P50 (P25 - P75) 25,3 (22,5 - 28,8), significativamente menor que los GOLD 3: 32,0 (27,5 - 34,0); p = 0,025. Se evidenció debilidad del cuádriceps (1RM/peso <0,60 1RM/IMC <120%), de forma global: 0,33 (0,22 - 0,41) y 93% (61 - 112) respectivamente, y en cada grupo, sin diferencias significativas entre ellos. Tampoco hubo diferencias significativas entre los grupos en las mediciones de ecografía muscular. La fuerza isotónica (1RM) se correlacionó con el grosor del cuádriceps QT (r = 0,529; p = 0,003) y el grosor del músculo vasto intermedio Q1(r = 0,514; p = 0,004) La fuerza isométrica se correlacionó con el QT (0,621; p <0,001), Q1 (0,441; p = 0,009) y el área transversal AQ (r = 0,587; p <0,001) Para cada grupo, el QT y la fuerza isométrica se correlacionaron significativamente. Conclusión: en nuestra serie de pacientes se demuestra la existencia de debilidad muscular del cuádriceps, independientemente del grado de severidad de la enfermedad y en estrecha relación con la masa muscular de dicho músculo. Palabras clave: disfunción muscular, fuerza isotónica, 1RM, fuerza isométrica, ecografía muscular

Objective: The objective of this study was to evaluate peripheral muscle function in patients with moderate-severe COPD by measuring isometric and isotonic muscular strength of the quadriceps and muscle mass through ultrasound. Method: This study included stable patients with moderate-severe COPD who were referred to pulmonary rehabilitation. In the dominant extremity, isometric strength (hydraulic dynamometer) and the 1RM test were measured and an ultrasound was done to determine the transversal area and dimensions of different sections of muscle. Results: 34 stable patients with COPD participated: GOLD 2 (n = 11), GOLD 3 (n = 12) and GOLD 4 (n = 11). GOLD 4 patients had a BMI P50 (P25 - P75) 25.3 (22.5 - 28.8), which was significantly lower than GOLD 3 patients: 32.0 (27.5 - 34.0); p = 0.025. Weakness in the quadriceps was observed (1 RM/weight <0.60; 1 RM/BMI <120%) overall: 0.33 (0.22 - 0.41) and 93% (61 - 112), respectively, and in each group, without significant differences between groups. There were also no significant differences between groups for ultrasound muscle measurements. Isotonic strength (1 RM) correlated to quadricep thickness QT (r = 0.529; p = 0.003) and vastus intermedius muscle thickness Q1(r = 0.514; p = 0.004). Isometric strength correlated to QT (0.621; p <0.001), Q1 (0.441; p = 0.009) and transversal area AQ (r = 0.587; p <0.001). QT and isometric strength were significantly correlated in each group. Conclusion: In our study, patients showed muscular weakness in the quadriceps, regardless of the degree of disease severity and this weakness was closely related to the mass of said muscle

Resposta aguda do exercício resistido dinâmico e isométrico em variáveis hemodinâmicas e autonômicas cardíacas em homens adultos / Respuesta aguda del ejercicio resistido dinámico y isométrico en variables hemodinámicas y autonómicas cardíacas en hombres adultos / Acute response to dynamic and isometric resistance exercise in hemodynamic and autonomic cardiac variables in male adults

Objetivo: Comparar respostas hemodinâmicas e autonômicas cardíacas após sessões agudas de exercício resistido dinâmico e isométrico. Método: Após familiarização às sessões experimentais e teste de uma repetição máxima, 12 homens (idade: 49.0±6.4 anos) sem o uso de medicamentos e experiência em exercício resistido foram randomizados de forma cruzada à duas sessões experimentais de exercício resistido dinâmico e isométrico compostos por um circuito de seis exercícios alternados por segmento corporal e à uma intensidade de 60% de uma repetição máxima. Aos momentos de repouso e recuperação foram mensuradas a pressão arterial sistólica e diastólica e registrado os intervalos R-R com posterior cálculo de índices da variabilidade da frequência cardíaca. Resultados: Não foram observadas diferenças estatisticamente significantes nas respostas pressóricas entre as sessões experimentais. O duplo produto se recuperou para valores basais aos 25min da recuperação em ambas as sessões. A frequência cardíaca permaneceu mais elevada durante momentos da recuperação na sessão dinâmico, ao passo que a sessão isométrica recuperou menos batimentos cardíacos para essa mesma variável. Adicionalmente, o balanço simpato-vagal permaneceu elevado e indicadores parassimpáticos diminuídos, em relação ao repouso, após sessão isométrica. Conclusão: Não ocorreram diferenças nas respostas hemodinâmicas entre as sessões de exercício resistido. Por outro lado, demonstrou-se diferentes recuperações para a frequência cardíaca e variáveis autonômicas após as sessões experimentais

Objetivo: Comparar respuestas hemodinámicas y autonómicas cardíacas después de sesiones agudas de ejercicio resistido dinámico y isométrico. Método: Después de familiarización en las sesiones experimentales y prueba de una repetición máxima, 12 hombres (edad: 49.0±6.4 años) sin el uso de medicamentos y experiencia en ejercicio resistido fueron randomizados de forma cruzada a dos sesiones experimentales de ejercicio resistido dinámico y isométricos compuestos por un circuito de seis ejercicios alternados por segmento corporal con una intensidad del 60% de una repetición máxima. Durante los momentos de reposo y recuperación se midieron la presión arterial sistólica y diastólica y se registraron los intervalos R-R con posterior cálculo de índices de la variabilidad de la frecuencia cardíaca. Resultados: No se observaron diferencias estadísticamente significativas en las respuestas de presión arterial entre las sesiones experimentales. El doble producto se recuperó a valores basales a los 25min de la recuperación en ambas sesiones. La frecuencia cardiaca permaneció más elevada durante momentos de recuperación en la sesión dinámica, mientras que la sesión isométrica recuperó menos latidos cardíacos para esa misma variable. Todavía, el balance simpático-vagal permaneció elevado e indicadores parasimpáticos disminuidos, en relación al reposo, después de la sesión isométrica. Conclusión: No ocurrieron diferencias en las respuestas hemodinámicas entre las sesiones de ejercicio. Sin embargo, se demostró diferentes recuperaciones entre las variables autonómicas después de las sesiones experimentales

Objective: To compare hemodynamic and cardiac autonomic responses after acute sessions of dynamic and isometric resistance exercise. Methods: After familiarization with the experimental sessions and maximal repetition test, 12 men (age: 49.0±6.4 years) without medication and experience in resistance exercise were cross-randomized in two experimental sessions of dynamic and isometric resistance exercise composed by a circuit with six alternating exercises per body segment and at intensities of 60% of a one maximum repetition. At rest and recovery moments, systolic and diastolic blood pressure were measured and R-R intervals were recorded with subsequent calculation of heart rate variability indexes. Results: No statistically significant differences were observed in blood pressure responses between experimental sessions. The rate pressure product recovered to baseline at 25min of recovery in both sessions. The heart rate remained higher during moments of recovery in the dynamic session, while the isometric session recovered fewer heart beats for that same variable. In addition, the sympatho-vagal balance remained high and the parasympathetic indicators decreased in relation to rest after the isometric session. Conclusion: There were no differences in hemodynamic response between resistance exercise sessions. Otherwise, different recoveries between the autonomic variables after the experimental sessions were demonstrated

Ankle Rotation and Muscle Loading Effects on the Calcaneal Tendon Moment Arm: An In Vivo Imaging and Modeling Study.

In this combined in vivo and computational modeling study, we tested the central hypothesis that ankle joint rotation and triceps surae muscle loading have independent and combinatory effects on the calcaneal (i.e., Achilles) tendon moment arm (CTma) that are not fully captured in contemporary musculoskeletal models of human movement. We used motion capture guided ultrasound imaging to estimate instantaneous variations in the CTma during a series of isometric and isotonic contractions compared to predictions from scaled, lower extremity computational models. As hypothesized, we found that muscle loading: (i) independently increased the CTma by up to 8% and (ii) attenuated the effects of ankle joint rotation, the latter likely through changes in tendon slack and tendon curvature. Neglecting the effects of triceps surae muscle loading in lower extremity models led to an underestimation of the CTma, on average, particularly in plantarflexion when those effects were most prominent. We also found little agreement between in vivo estimates and model predictions on an individual subject by subject basis, alluding to unaccounted for variation in anatomical morphology and thus fundamental limitations in model scaling. Together, these findings contribute to improving our understanding of the physiology of ankle moment and power generation and novel opportunities for model development.

Comparative performance of isometric and isotonic quadriceps strength testing in total knee arthroplasty.

BACKGROUND: Early quadriceps muscle strength assessment after a total knee arthroplasty (TKA) provides timely information on progress, but little is known about the pain profile and predictive validity associated with common clinical muscle strength tests. This study aimed to, in patients with a recent TKA, examine the associations of isometric and isotonic quadriceps strength with gait speed, accounting for knee pain experienced during testing. METHODS: A sample of 76 patients (mean age 68 years; 46 women) with a recent TKA (median, 1.5 months) participated. Quadriceps strength was measured on both limbs using a knee extension machine. Isotonic strength was assessed with a one-repetition maximum test. Isometric strength was measured at 40° and 70° of knee flexion using a custom-built load cell. To allow for valid comparisons between the tests, quadriceps strength symmetry ratios were calculated. Knee pain during testing was measured using an 11-point pain scale. Fast gait speed was measured using the 10-m walk test. RESULTS: Compared with isotonic test, quadriceps strength ratio was higher for the 40° flexion isometric test (P = 0.01), and this difference may be explained by the lower knee pain intensity elicited during the isometric tests (P's < 0.001). All strength measures were closely associated with fast gait speed after adjustment for knee pain and covariates (P's < 0.001). CONCLUSIONS: Early in the post-TKA period, isometric and isotonic strength tests may be used to assess quadriceps strength but these tests are not interchangeable. Isometric quadriceps testing may be preferable to isotonic testing as it was associated with lower knee pain intensity.

Do isometric, isotonic and/or isokinetic strength trainings produce different strength outcomes?

INTRODUCTION: Several studies have been developed to determine which type of muscular action (isometric, isotonic and isokinetic) elicits more gains in functional strength and muscle mass. The comparisons between training outcomes are inconclusive due to lack of exercise standardization. OBJECTIVE: To compare muscle strength, mass, and functional performance in response to isometric, isotonic, and isokinetic contractions, when training loads (volume and intensity) are equated. METHOD: Data were derived from a university community-recruited sample (n = 31 men). INTERVENTIONS: Untrained men were assigned to isotonic (IT), isometric (IM), or isokinetic (IK) group, and trained their dominant quadriceps muscle 3 sessions/week for 8 weeks with a dynamometer. Muscle strength was assessed using Cybex 6000 dynamometer; the triple-hop-distance test was used to assess functional performance, and dual energy x-ray absorptiometry to assess lean muscle mass. RESULTS: After training, muscle lean muscle mass increased in isometric (+3.1%, p < 0.01) and isotonic groups (+3.9%, p < 0.01); only the isokinetic group showed a significant improvement in the triple-hop-distance test (4.84%, p < 0.01). CONCLUSION: Clinicians should consider isometric training as an alternative for isotonic training to gain muscle mass, and isokinetic training to improve functional performance of daily activities and/or sports.

Force-velocity relationship during isometric and isotonic fatiguing contractions.

Fatiguing contractions change the force-velocity relationship, but assessment of this relationship in fatigue has usually been obtained after isometric contractions. We studied fatigue caused by isometric or isotonic contractions, by assessment of the force-velocity relationship while the contractions maintaining fatigue were continued. This approach allowed determination of the force-velocity relationship during a steady condition of fatigue. We used the in situ rat medial gastrocnemius muscle, a physiologically relevant preparation. Intermittent (1/s) stimulation at 170 Hz for 100 ms resulted in decreased isometric force to ~35% of initial or decreased peak velocity of shortening in dynamic contractions to ~45% of initial. Dynamic contractions resulted in a transient initial increase in velocity, followed by a rapid decline until a reasonably steady level was maintained. Data were fit to the classic Hill equation for determination of the force-velocity relationship. Isometric and dynamic contractions resulted in similar decreases in maximal isometric force and peak power. Only Vmax was different between the types of contraction ( P < 0.005) with greater decrease in Vmax during isotonic contractions to 171.7 ± 7.3 mm/s than during isometric contractions to 208.8 mm/s. Curvature indicated by a/Po (constants from fit to Hill equation) changed from 0.45 ± 0.04 to 0.71 ± 0.11 during isometric contractions and from 0.51 ± 0.04 to 0.85 ± 0.18 during isotonic contractions. Recovery was incomplete 45 min after stopping the intermittent contractions. At this time, recovery of low-frequency isometric force was substantially less after isometric contractions, implicating force during intermittent contractions as a determining factor with this measure of fatigue. NEW & NOTEWORTHY The force-velocity relationship was captured while fatigue was maintained at a constant level during isometric and dynamic contractions. The curvature of the force-velocity relationship was less curved during fatigue than prefatigued, but within 45 min this recovered. Low-frequency fatigue persisted with greater depression of low-frequency force after isometric contractions, possibly because of higher force contractions during intermittent contractions.

Isokinetic peak torque and flexibility changes of the hamstring muscles after eccentric training: Trained versus untrained subjects.

OBJECTIVE: The aim of this study was to examine the effect of eccentric isotonic training on hamstring flexibility and eccentric and concentric isokinetic peak torque in trained and untrained subjects. METHODS: Sixty healthy subjects (mean age: 21.66 ± 2.64) were divided into three equal groups, each with 20 voluntary participants. Two experimental groups (untrained and trained groups) participated in a hamstring eccentric isotonic strengthening program (five days/week) for a six-week period and one control group that was not involved in the training program. The passive knee extension range of motion and hamstring eccentric and concentric isokinetic peak torque were measured at angular velocities 60° and 120°/s for all groups before and after the training period. RESULTS: Two-way analysis of variance showed that there was a significant increase in the hamstring flexibility of the untrained and trained groups (25.65 ± 6.32°, 26.55 ± 5.99°, respectively), (p < 0.05) without a significant increase in the control group (31.55 ± 5.84°), (p > 0.05). Moreover, there was a significant increase in eccentric isokinetic peak torque of both the untrained and trained groups (127.25 ± 22.60Nm, 139.65 ± 19.15Nm, 125.40 ± 21.61Nm, 130.90 ± 18.71Nm, respectively), (p < 0.05) without a significant increase in the control group (109.15 ± 20.89Nm, 105.70 ± 21.31Nm, respectively), (p > 0.05) at both angular velocities. On the other hand, there was no significant increase in the concentric isokinetic peak torque of the three groups (92.50 ± 20.50Nm, 79.05 ± 18.95Nm, 92.20 ± 21.96Nm, 79.85 ± 18.97Nm, 100.45 ± 25.78Nm, 83.40 ± 23.73Nm, respectively), (p > 0.05) at both angular velocities. The change scores in the hamstring flexibility (06.25 ± 1.86°) and eccentric peak torque of the untrained group (16.60 ± 4.81Nm, 17.45 ± 5.40Nm, respectively) were significantly higher (p < 0.05) than those of the trained group (03.40 ± 1.14°, 9.90 ± 5.14Nm, 9.80 ± 7.57Nm, respectively), and the control group (00.90 ± 2.10°, 0.60 ± 2.93Nm, 1.40 ± 3.53Nm, respectively), at both angular velocities. Meanwhile, the change scores of the concentric peak torques of the three groups (1.15 ± 1.50Nm, -0.15 ± 2.16Nm, 1.35 ± 1.63Nm, 0.20 ± 2.95Nm, 0.60 ± 2.28Nm, -0.30 ± 2.25Nm) were statistically insignificant (p > 0.05). CONCLUSION: After a six-week period of eccentric isotonic training, the hamstring eccentric peak torque and flexibility of trained and untrained groups improved without changes in the concentric peak torque. Moreover, the improvement of untrained subjects was higher than trained subjects. These findings may be helpful in designing the hamstring rehabilitation program.

The profile of upper extremity muscular strength in female wheelchair basketball players: a pilot study.

BACKGROUND: The purpose of this study was to analyze and compare the profile of upper extremity muscle strength in female wheelchair basketball players with that of sex-matched non-disabled controls. METHODS: Nineteen female subjects were enrolled in this study. These were divided into two groups. Group 1 (N.=10) consisted of wheelchair basketball players and Group 2 (N.=9) of non-disabled individuals. Muscular strength in the shoulder was measured using an isokinetic dynamometer. Isometric and isotonic muscular endurance in the shoulder joint was evaluated in terms of the length of time subjects could hold a 5-kg dumbbell at 45° and the number of abduction repetitions to 45° with a 5-kg dumbbell in 30 seconds, respectively. Pinch strength and hand grip strength were measured using a Pinch gauge and hand dynamometer, respectively. RESULTS: Significant differences were observed between the groups in terms of all parameters of muscular strength in the shoulder joint, hand grip and pinch strength. Upper extremity muscular strength in female wheelchair basketball players was greater than in the non-disabled controls. CONCLUSIONS: We concluded that the difference in muscle strength between the groups mostly derived from using wheelchairs due to players' intense training and busy match schedules. Additionally, the profile of upper extremity muscle strength in female wheelchair basketball players in our study can be used as basic data for the introduction of exercise rehabilitation programs and as a guide for future research.

Regional variation in the mechanical properties and fibre-type composition of the rat extensor digitorum longus muscle.

NEW FINDINGS: What is the central question of this study? Mammalian muscle is typically heterogeneous in fibre-type distribution, with distinct regional variation in composition. The effects this might have on mechanical performance are largely unknown. What is the main finding and its importance? Contractile properties vary regionally within a heterogeneous muscle. The mixed extensor digitorum longus muscle has phenotypically distinct compartments that differ in their isometric twitch kinetics, the optimal cycle frequency for maximal power generation and fatigue resistance. The mechanisms underpinning the decline in performance during fatigue differ between compartments. Regional variation in mechanical performance suggests that regions of the extensor digitorum longus muscle might be differentially recruited during locomotion, depending upon functional demand. Fibre-type composition is heterogeneous, and distribution varies spatially in many muscles, indicating that there might be regional variation in recruitment and mechanical output. The rat extensor digitorum longus muscle is composed of predominantly fast-twitch fibres and exhibits a gradient in phenotype, resulting in oxidative medial (areal composition 24.3% type I/IIa) and glycolytic lateral (92.4% type IIx/IIb) compartments. Here, we investigated the variation in mechanical performance between the medial and lateral compartments during isometric, isotonic and cyclical contractions. Isometric tetanic stress and force-velocity relationships were similar in both compartments, but isometric twitch kinetics were slower in the medial compared with the lateral compartment. The medial compartment also had a lower optimal cycle frequency for maximal net power generation (11 versus 15 Hz; P < 0.05) attributable to slower isometric kinetics, resulting in a lower level of activation and reduced net work generation at higher cycle frequencies, compared with the lateral compartment. The more oxidative, medial compartment had higher fatigue resistance, maintaining net power 26% longer than the lateral compartment. The predominant mechanisms underpinning the decrease in net power varied between the compartments, resulting from an increase in the work to extend the muscle and from a reduction in work during shortening in the medial and lateral compartments, respectively. Regional variation in mechanical performance and resistance to fatigue within a mixed muscle suggests that a differential recruitment pattern is likely during locomotion, with the medial compartment being used during slow-speed locomotion and the lateral compartment during burst activities.

Effect of localised vibration on muscle strength in healthy adults: a systematic review.

OBJECTIVE: To investigate the effects of local vibration on muscle strength in healthy adults. DATA SOURCES: The electronic databases PubMed, CINAHL, Scopus and Web of Science were searched using a combination of the following keywords: vibration, vibration therapy, power, maximal voluntary contraction, performance, rate of force development and vibratory exercise. In addition, the Medical Subject Headings 'vibration', 'strength' and 'exercise' were used. The bibliographical search was limited to articles published in English. STUDY SELECTION: Trials that evaluated the effect of localised vibration on muscle strength in healthy humans were included. DATA EXTRACTION: Two independent evaluators verified the quality of the selected studies using the PEDro Scale and the Cochrane Collaboration's tool for assessing the risk of bias. Muscle strength was calculated for each intervention. RESULTS: In total, 29 full-text studies were assessed for eligibility. Eighteen studies did not match the inclusion criteria, and were excluded. The 11 studies included in this review had an average PEDro score of 5.36/10. Most of the studies reported significant improvements in muscle strength after the application of local vibration. There was considerable variation in the vibration training parameters and target muscle location. CONCLUSIONS: The use of local vibration on the target muscle can enhance muscle strength in healthy adults. Further well-designed controlled studies are required to confirm the effect of local vibration training on muscle strength.

Utilizing Physiological Principles of Motor Unit Recruitment to Reduce Fatigability of Electrically-Evoked Contractions: A Narrative Review.

Neuromuscular electrical stimulation (NMES) is used to produce contractions to restore movement and reduce secondary complications for individuals experiencing motor impairment. NMES is conventionally delivered through a single pair of electrodes over a muscle belly or nerve trunk using short pulse durations and frequencies between 20 and 40Hz (conventional NMES). Unfortunately, the benefits and widespread use of conventional NMES are limited by contraction fatigability, which is in large part because of the nonphysiological way that contractions are generated. This review provides a summary of approaches designed to reduce fatigability during NMES, by using physiological principles that help minimize fatigability of voluntary contractions. First, relevant principles of the recruitment and discharge of motor units (MUs) inherent to voluntary contractions and conventional NMES are introduced, and the main mechanisms of fatigability for each contraction type are briefly discussed. A variety of NMES approaches are then described that were designed to reduce fatigability by generating contractions that more closely mimic voluntary contractions. These approaches include altering stimulation parameters, to recruit MUs in their physiological order, and stimulating through multiple electrodes, to reduce MU discharge rates. Although each approach has unique advantages and disadvantages, approaches that minimize MU discharge rates hold the most promise for imminent translation into rehabilitation practice. The way that NMES is currently delivered limits its utility as a rehabilitative tool. Reducing fatigability by delivering NMES in ways that better mimic voluntary contractions holds promise for optimizing the benefits and widespread use of NMES-based programs.

The contractile adaption to preload depends on the amount of afterload.

AIMS: The Frank-Starling mechanism (rapid response (RR)) and the secondary slow response (SR) are known to contribute to increases contractile performance. The contractility of the heart muscle is influenced by pre-load and after-load. Because of the effect of pre-load vs. after-load on these mechanisms in not completely understood, we studied the effect in isolated muscle strips. METHODS AND RESULTS: Progressive stretch lead to an increase in shortening/force development under isotonic (only pre-load) and isometric conditions (pre- and after-load). Muscle length with maximal function was reached earlier under isotonic (Lmax-isotonic ) compared with isometric conditions (Lmax-isometric ) in nonfailing rabbit, in human atrial and in failing ventricular muscles. Also, SR after stretch from slack to Lmax-isotonic was comparable under isotonic and isometric conditions (human: isotonic 10 ± 4%, isometric 10 ± 4%). Moreover, a switch from isotonic to isometric conditions at Lmax-isometric showed no SR proving independence of after-load. To further analyse the degree of SR on the total contractile performance at higher pre-load muscles were stretched from slack to 98% Lmax-isometric under isotonic conditions. Thereby, the SR was 60 ± 9% in rabbit and 51 ± 14% in human muscle strips. CONCLUSIONS: This work shows that the acute contractile response largely depends on the degree and type of mechanical load. Increased filling of the heart elevates pre-load and prolongs the isotonic part of contraction. The reduction in shortening at higher levels of pre-load is thereby partially compensated by the pre-load-induced SR. After-load shifts the contractile curve to a better 'myofilament function' by probably influencing thin fibers and calcium sensitivity, but has no effect on the SR.

Associations of isokinetic and isotonic knee strength with knee function and activity level after anterior cruciate ligament reconstruction: a prospective cohort study.

BACKGROUND: Although isokinetic dynamometry often serves as a reference to assess the concurrent validity of weight-machine isotonic strength testing, it is unknown whether isokinetic knee strength is associated with knee function and activity level more strongly than isotonic knee strength in patients with an anterior cruciate ligament reconstruction (ACLR). This study aimed to compare the associations of isokinetic and isotonic knee strength with knee function and work-and-sports activity levels in patients with ACLR. METHODS: One-hundred and six patients with a unilateral ACLR participated. At three months post-ACLR, isokinetic quadriceps and hamstrings strength was measured using an isokinetic dynamometer whilst isotonic strength was measured using weight machines. At six months post-ACLR, patients performed the single-leg hop-for-distance test. Self reported knee function and work-and-sports activity levels were assessed by the Lysholm Knee Score and Tegner Activity Score, respectively. RESULTS: In multivariable analyses, isotonic and isokinetic quadriceps strength limb symmetry indices (LSIs) were significantly associated with all outcomes (P≤0.03) and had comparable predictive performance. Isotonic and isokinetic hamstrings strength LSIs were significantly associated with Lysholm scores (P≤0.03) and isotonic hamstrings strength was additionally significantly associated with hop-for-distance LSI (P=0.01). CONCLUSIONS: Weight machine-derived isotonic quadriceps strength was independently and consistently associated with knee function and work-and-sport activity level post-ACLR. Isokinetic knee strength was not more strongly associated than isotonic knee strength with the various outcomes. These findings have logistic and economic implications because the isokinetic dynamometer system is relatively expensive and its operation requires more logistic effort and technical skills.

Mathematical model for isometric and isotonic muscle contractions.

A new mathematical model is presented to describe both the active and passive mechanics of muscles. In order to account for the active response, a two-layer kinematics that introduces both the visible and rest lengths of the muscle is presented within a rational mechanics framework. The formulation is based on an extended version of the principle of virtual power and the dissipation principle. By using an accurate constitutive description of muscle mobility under activation, details of microscopic processes that lead to muscle contraction are glossed over while macroscopic effects of chemical/electrical stimuli on muscle mechanics are retained. The model predictions are tested with isometric and isotonic experimental data collected from murine extensor digitorum muscle. It is shown that the proposed model captures experimental observations with only three scalar parameters.