Knee movements cause changes in the firing behaviour of muscle spindles located within the mono-articular ankle extensor soleus in the rat.

We recently showed that within an intact muscle compartment, changing the length of one muscle affects the firing behaviour of muscle spindles located within a neighbouring muscle. The conditions tested, however, involved muscle lengths and relative positions that were beyond physiological ranges. The aim of the present study was to investigate the effects of simulated knee movements on the firing behaviour of muscle spindles located within rat soleus (SO) muscle. Firing from single muscle spindle afferents in SO was measured intra-axonally for different lengths (static) and during lengthening (dynamic) of the lateral gastrocnemius and plantaris muscles. Also, the location of the spindle within the muscle was assessed. Changing the length of synergistic ankle plantar flexors (simulating different static knee positions, between 45 and 130°) affected the force threshold, but not the length threshold, of SO muscle spindles. The effects on type II afferents were substantially (four times) higher than those on type IA afferents. Triangular stretch-shortening of synergistic muscles (simulating dynamic knee joint rotations of 15°) caused sudden changes in the firing rate of SO type IA and II afferents. Lengthening decreased and shortening increased the firing rate, independent of spindle location. This supports our prediction that the major point of application of forces exerted by connections between adjacent muscles is at the distal end of SO. We conclude that muscle spindles provide the CNS with information about the condition of adjacent joints that the muscle does not span.

Improved Postoperative Outcomes after Prehabilitation for Colorectal Cancer Surgery in Older Patients: An Emulated Target Trial.

BACKGROUND: The aim of this study was to assess the effect of a multimodal prehabilitation program on perioperative outcomes in colorectal cancer patients with a higher postoperative complication risk, using an emulated target trial (ETT) design. PATIENTS AND METHODS: An ETT design including overlap weighting based on propensity score was performed. The study consisted of all patients with newly diagnosed colorectal cancer (2016-2021), in a large nonacademic training hospital, who were candidate to elective colorectal cancer surgery and had a higher risk for postoperative complications defined by: age ≥ 65 years and or American Society of Anesthesiologists score III/IV. Intention-to-treat (ITT) and per-protocol analyses were performed to evaluate the effect of prehabilitation compared with usual care on perioperative complications and length of stay (LOS). RESULTS: Two hundred fifty-one patients were included: 128 in the usual care group and 123 patients in the prehabilitation group. In the ITT analysis, the number needed to treat to reduce one or more complications in one person was 4.2 (95% CI 2.6-10). Compared with patients in the usual care group, patients undergoing prehabilitation had a 55% lower comprehensive complication score (95% CI -71 to -32%). There was a 33% reduction (95% CI -44 to -18%) in LOS from 7 to 5 days. CONCLUSIONS: This study showed a clinically relevant reduction of complications and LOS after multimodal prehabilitation in patients undergoing colorectal cancer surgery with a higher postoperative complication risk. The study methodology used may serve as an example for further larger multicenter comparative effectiveness research on prehabilitation.

Morphology of proximal and distal human semitendinosus compartments and the effects of distal tendon harvesting for anterior cruciate ligament reconstruction.

The human semitendinosus muscle is characterized by a tendinous inscription separating proximal and distal neuromuscular compartments. As each compartment is innervated by separate nerve branches, potential exists for independent operation and control of compartments. However, the morphology and function of each compartment have not been thoroughly examined in an adult human population. Further, the distal semitendinosus tendon is typically harvested for use in anterior cruciate ligament reconstruction surgery, which induces long-term morphological changes to the semitendinosus muscle-tendon unit. It remains unknown if muscle morphological alterations following anterior cruciate ligament reconstruction are uniform between proximal and distal semitendinosus compartments. Here, we performed magnetic resonance imaging on 10 individuals who had undergone anterior cruciate ligament reconstruction involving an ipsilateral distal semitendinosus tendon graft 14 ± 4 months prior, extracting morphological parameters of the whole semitendinosus muscle and each individual compartment from both the (non-injured) contralateral and surgical legs. In the contralateral leg, volume and length of the proximal compartment were smaller than the distal compartment. No between-compartment differences in volume or length were found for anterior cruciate ligament reconstructed legs, likely due to greater shortening of the distal compared to the proximal compartment after anterior cruciate ligament reconstruction. The maximal anatomical cross-sectional area of both compartments was substantially smaller on the anterior cruciate ligament reconstructed leg but did not differ between compartments on either leg. The absolute and relative between-leg differences in proximal compartment morphology on the anterior cruciate ligament reconstructed leg were strongly correlated with the corresponding between-leg differences in distal compartment morphological parameters. Specifically, greater between-leg morphological differences in one compartment were highly correlated with large between-leg differences in the other compartment, and vice versa for smaller differences. These relationships indicate that despite the heterogeneity in compartment length and volume, compartment atrophy is not independent or random. Further, the tendinous inscription endpoints were generally positioned at the same proximodistal level as the compartment maximal anatomical cross-sectional areas, providing a wide area over which the tendinous inscription could mechanically interact with compartments. Overall, results suggest the two human semitendinosus compartments are not mechanically independent.

Three-Dimensional Interactive Graphical Model of the Hindlimb Muscles of the Rat.

Many questions in human movement sciences are addressed by exploiting the advantages of animal models. However, a 3D graphical model of the musculoskeletal system of the frequently used rat model that includes a sufficient level of detail does not exist. Therefore, the aim of the present work was to develop an freely accessible 3D graphical model of the rat hindlimb. Using the anatomical data of the Wistar rat (Mus norvegicus albinus) published by Greene [1935], a 3D representation of 34 muscles of the hindlimb was drawn. Two models were created, one using muscle-like appearances and one using different colors. Each muscle can be viewed separately or within the context of its synergistic and antagonistic muscles. This model can serve to train new students before starting their experiments but also for producing illustrations of experimental conditions or results. Further development of the model will be needed to equip it with the same advanced functionalities of some of the human anatomy atlases.

Activity distribution among the hamstring muscles during high-speed running: A descriptive multichannel surface EMG study.

PURPOSE: This study assessed activity distribution among the hamstring muscles during high-speed running. The objective was to compare within and between muscle activity, relative contribution and hip and knee joint angles at peak muscle activity during high-speed running. METHODS: Through multichannel electromyography, we measured muscle activity in male basketball players during high-speed running on a treadmill at 15 locations: five for biceps femoris long head, four for semitendinosus, and six for semimembranosus. Muscle activity was calculated for each location within each hamstring muscle individually for each percent of a stride cycle. RESULTS: Twenty-nine non-injured basketball players were included (mean age: 17 ± 1 years; mass, 85 ± 9 kg; height, 193 ± 9 cm). Heterogeneous activity was found for all individual hamstring muscles across multiple events of the stride cycle. In the late-swing phase, muscle activity and relative contribution of the semimembranosus was significantly higher than of the semitendinosus. There was no significant difference in hip and knee joint angles at instant of peak muscle activity, assessed locally within individual hamstring muscles, as well as in general over the whole hamstring muscle. CONCLUSION: Hamstring muscles were most active in the late-swing phase during high-speed running. In this phase, the semimembranosus was most active and the semitendinosus was least active. Within the biceps femoris long head, the most proximal region was significantly more active in the late-swing phase, compared to other muscle regions. For each muscle and location, peak muscle activity occurred at similar hip and knee joint angles.

The Effect of the Nordic Hamstring Exercise on Muscle Activity: A Multichannel Electromyography Randomized Controlled Trial.

The aim of this study was to evaluate the effect of a Nordic hamstring exercise intervention on biceps femoris long head, semitendinosus, and semimembranosus muscle's activity and relative contributions through multichannel electromyography. Twenty-four injury-free male basketball players (mean age 20 [3] y) were randomly assigned to a 12-week intervention (n = 13) or control group (n = 11). The primary outcome measures were normalized muscle activity (percentage of maximal voluntary isometric contraction, %MVIC) and relative contribution of hamstring muscles over 12 weeks. No effects were found on any of the primary outcome measures. Between-group differences over 12 weeks were 2.7%MVIC (95% confidence interval 95% CI, -0.7 to 6.1) for the biceps femoris long head, 3.4%MVIC (95% CI, -1.4 to 8.2) for the semitendinosus, and 0.8%MVIC (95% CI, -3.0 to 4.6) for the semimembranosus, P = .366. Between-group differences over 12 weeks were 1.0% relative contribution (%con; 95% CI, -3.0 to 5.1) for the biceps femoris long head, 2.2% relative contribution (95% CI, -2.8 to 7.2) for the semitendinosus, and -3.3% relative contribution (95% CI, -6.4 to -0.1) for the semimembranosus P = .258. A positive value implies a higher value for the Nordic group. A Nordic hamstring exercise intervention did not affect the level of muscle activity and relative contribution of hamstring muscles in performance of the Nordic hamstring exercise.

Activity Distribution Among the Hamstring Muscles During the Nordic Hamstring Exercise: A Multichannel Surface Electromyography Study.

This study assessed activity distribution among the hamstring muscles during the Nordic hamstring exercise (NHE). The objective was to compare muscle activity between and within muscles during the NHE to add insights in its underlying protective mechanism. Through multichannel electromyography, we measured muscle activity in male basketball players during the NHE. Electromyography was assessed at 15 locations: 5 for biceps femoris long head, 4 for semitendinosus, and 6 for semimembranosus. For each percent of the eccentric phase of the NHE, muscle activity was calculated for each electrode location within each hamstring muscle individually. To quantify whole muscle head activity, means and variances across electrodes within each muscle were calculated. Thirty-five noninjured participants were included (mean age, 18 [2] y; mass, 87 [12] kg; height, 192 [9] cm). Heterogeneous muscle activity was found between 38% and 62% and over the whole eccentric contraction phase within the semitendinosus and the semimembranosus, respectively. Muscle activity of the semitendinosus was significantly higher than that of the biceps femoris long head. During the NHE, the relative contribution of the semitendinosus is the highest among hamstring muscles. Its strong contribution may compensate for the biceps femoris long head, the most commonly injured hamstring muscle head.

Altered neural control of gait and its association with pain and joint impairment in adults with haemophilic arthropathy: Clinical and methodological implications.

INTRODUCTION: It is unknown whether altered neural control is associated with clinical outcomes in people with haemophilic arthropathy (PWHA). The dynamic motor control index during walking (Walk-DMC) is a summary metric of neural control. AIMS: The primary aim of this study was to apply the Walk-DMC to assess if people diagnosed with haemophilic arthropathy have impaired neural control of gait and investigate the association of Walk-DMC with pain and joint impairment. METHOD: The Walk-DMC was assessed using surface electromyography in 11 leg muscles. Twenty-two PWHA and 15 healthy subjects walked on a 30-m walkway at 1 m/s. In addition, pain (visual analogue scale), knee flexion contracture (degrees) and joint impairment (Haemophilia Joint Health Score, HJHS) were assessed. The clinical outcomes were correlated with the Walk-DMC. Multiple regression analysis was performed to predict the Walk-DMC using the clinical outcomes. RESULTS: In 13 PWHA the Walk-DMC was beyond the normal range (80-120 pts). PWHA with an altered Walk-DMC showed more years with arthropathy, more pain, higher knee flexion contracture and a higher HJHS score (P < .05, effect size > .8). Significant negative moderate associations between Walk-DMC and pain, knee flexion contracture and HJHS were found (P < .05). The model that best predicted the Walk-DMC was the pain with knee flexion contracture (R2  = .44; P = .004). CONCLUSIONS: PWHA with abnormal neural control of gait also has more years with arthropathy, more pain, and more impaired joints. Our results indicate an association between the Walk-DMC index and joint damage, specifically with pain in combination with knee flexion contracture.

Detection of epimuscular myofascial forces by Golgi tendon organs.

Skeletal muscles embed multiple tendon organs, both at the proximal and distal ends of muscle fibers. One of the functions of such spatial distribution may be to provide locally unique force feedback, which may become more important when stresses are distributed non-uniformly within the muscle. Forces exerted by connections between adjacent muscles (i.e. epimuscular myofascial forces) may cause such local differences in force. The aim of this exploratory study was to investigate the effects of mechanical interactions between adjacent muscles on sensory encoding by tendon organs. Action potentials from single afferents were recorded intra-axonally in response to ramp-hold release (RHR) stretches of a passive agonistic muscle at different lengths or relative positions of its passive synergist. The tendons of gastrocnemius (GAS), plantaris (PL) and soleus (SO) muscles were cut from the skeleton for attachment to servomotors. Connective tissues among these muscles were kept intact. Lengthening GAS + PL decreased the force threshold of SO tendon organs (p = 0.035). The force threshold of lateral gastrocnemius (LG) tendon organs was not affected by SO length (p = 0.371). Also displacing LG + PL, kept at a constant muscle-tendon unit length, from a proximal to a more distal position resulted in a decrease in force threshold of LG tendon organs (p = 0.007). These results indicate that tendon organ firing is affected by changes in length and/or relative position of adjacent synergistic muscles. We conclude that tendon organs can provide the central nervous system with information about local stresses caused by epimuscular myofascial forces.

Implementation of prehabilitation in colorectal cancer surgery: qualitative research on how to strengthen facilitators and overcome barriers.

PURPOSE: Prehabilitation is increasingly offered to patients with colorectal cancer (CRC) undergoing surgery as it could prevent complications and facilitate recovery. However, implementation of such a complex multidisciplinary intervention is challenging. This study aims to explore perspectives of professionals involved in prehabilitation to gain understanding of barriers or facilitators to its implementation and to identify strategies to successful operationalization of prehabilitation. METHODS: In this qualitative study, semi-structured interviews were performed with healthcare professionals involved in prehabilitation for patients with CRC. Prehabilitation was defined as a preoperative program with the aim of improving physical fitness and nutritional status. Parallel with data collection, open coding was applied to the transcribed interviews. The Ottawa Model of Research Use (OMRU) framework, a comprehensive interdisciplinary model guide to promote implementation of research findings into healthcare practice, was used to categorize obtained codes and structure the barriers and facilitators into relevant themes for change. RESULTS: Thirteen interviews were conducted. Important barriers were the conflicting scientific evidence on (cost-)effectiveness of prehabilitation, the current inability to offer a personalized prehabilitation program, the complex logistic organization of the program, and the unawareness of (the importance of) a prehabilitation program among healthcare professionals and patients. Relevant facilitators were availability of program coordinators, availability of physician leadership, and involving skeptical colleagues in the implementation process from the start. CONCLUSIONS: Important barriers to prehabilitation implementation are mainly related to the intervention being complex, relatively unknown and only evaluated in a research setting. Therefore, physicians' leadership is needed to transform care towards more integration of personalized prehabilitation programs. IMPLICATIONS FOR CANCER SURVIVORS: By strengthening prehabilitation programs and evidence of their efficacy using these recommendations, it should be possible to enhance both the pre- and postoperative quality of life for colorectal cancer patients during survivorship.

Characteristics and outcomes of older patients hospitalised for COVID-19 in the first and second wave of the pandemic in The Netherlands: the COVID-OLD study.

BACKGROUND: as the coronavirus disease of 2019 (COVID-19) pandemic progressed diagnostics and treatment changed. OBJECTIVE: to investigate differences in characteristics, disease presentation and outcomes of older hospitalised COVID-19 patients between the first and second pandemic wave in The Netherlands. METHODS: this was a multicentre retrospective cohort study in 16 hospitals in The Netherlands including patients aged ≥ 70 years, hospitalised for COVID-19 in Spring 2020 (first wave) and Autumn 2020 (second wave). Data included Charlson comorbidity index (CCI), disease severity and Clinical Frailty Scale (CFS). Main outcome was in-hospital mortality. RESULTS: a total of 1,376 patients in the first wave (median age 78 years, 60% male) and 946 patients in the second wave (median age 79 years, 61% male) were included. There was no relevant difference in presence of comorbidity (median CCI 2) or frailty (median CFS 4). Patients in the second wave were admitted earlier in the disease course (median 6 versus 7 symptomatic days; P < 0.001). In-hospital mortality was lower in the second wave (38.1% first wave versus 27.0% second wave; P < 0.001). Mortality risk was 40% lower in the second wave compared with the first wave (95% confidence interval: 28-51%) after adjustment for differences in patient characteristics, comorbidity, symptomatic days until admission, disease severity and frailty. CONCLUSIONS: compared with older patients hospitalised in the first COVID-19 wave, patients in the second wave had lower in-hospital mortality, independent of risk factors for mortality.The better prognosis likely reflects earlier diagnosis, the effect of improvement in treatment and is relevant for future guidelines and treatment decisions.

Trajectories and prognostic factors for recovery after hip fracture: a longitudinal cohort study.

PURPOSE: The aim of this study was to determine recovery trajectories and prognostic factors for poor recovery in frail and non-frail patients after hip fracture. METHODS: Patients with a hip fracture aged 65 years and older admitted to a hospital in the Netherlands from August 2015 to November 2016 were asked to complete questionnaires at one week and one, three, six, 12, and 24 months after injury. The questionnaires included the ICEpop CAPability measure for older people, Health Utility Index, and the Hospital Anxiety Depression Scale. Latent class trajectory analysis was used to determine trajectories of recovery. Patient and injury characteristics for favourable and unfavourable outcome were compared with logistic regression. RESULTS: In total, 696 patients were included of which 367 (53%) patients were frail. Overall, recovery trajectories in frail patients were worse compared to trajectories in non-frail patients. In frail patients, poor recovery was significantly associated with dementia. Lower age was a prognostic factor for good recovery. Immobility, loneliness and weight loss were prognostic for respectively poor capability and symptoms of anxiety and depression. In non-frail patients, recovery after hip fracture was associated with loneliness and the type of hip fracture. CONCLUSION: Although frailty is associated with poor recovery in older patients with hip fracture, a large proportion of frail patients show good recovery. Loneliness determines poor recovery with anxiety and depressive symptoms. TRAIL REGISTRATION: ClinicalTrials.gov identifier: NCT02508675 (July 27, 2015).

Modular reorganization of gait in chronic but not in artificial knee joint constraint.

It is currently unknown if modular reorganization does occur if not the central nervous system, but the musculoskeletal system is affected. The aims of this study were to investigate 1) the effects of an artificial knee joint constraint on the modular organization of gait in healthy subjects; and 2) the differences in modular organization between healthy subjects with an artificial knee joint constraint and people with a similar but chronic knee joint constraint. Eleven healthy subjects and eight people with a chronic knee joint constraint walked overground at 1 m/s. The healthy subjects also walked with a constraint limiting knee joint movement to 20°. The total variance accounted (tVAF) for one to four synergies and modular organization were assessed using surface electromyography from 11 leg muscles. The distribution of number of synergies were not significantly different between groups. The tVAF and the motor modules were not significantly affected by the artificial knee constraint. A higher tVAF for one and two synergies, as well as merging of motor modules were observed in the chronic knee constraint group. We conclude that in the short-term a knee constraint does not affect the modular organization of gait, but in the long-term a knee constraint results in modular reorganization. These results indicate that merging of motor modules may also occur when changes in the mechanics of the musculoskeletal system is the primary cause of the motor impairment.NEW & NOTEWORTHY It is currently unknown if modular reorganization does occur if not the central nervous system, but the musculoskeletal system is affected. This study showed that in the short-term a knee constraint does not affect the modular organization of gait, but in the long-term a knee constraint results in modular reorganization. These results indicate that modular reorganization may also occur when changes in the mechanics of the musculoskeletal system is the primary cause of the motor impairment.

Primary Anastomosis Versus End-Ostomy in Left-Sided Colonic and Proximal Rectal Cancer Surgery in the Elderly Dutch Population: A Propensity Score Matched Analysis.

BACKGROUND: Primary anastomosis (PA) in left-sided colorectal cancer (CRC) surgery in elderly patients is disputed. The aim of our study was to evaluate the differences in postoperative outcomes after left-sided CRC surgery in elderly patients in The Netherlands, comparing patients with PA and those who underwent end-ostomy (EO). METHOD: Patients aged ≥ 75 years with stage I-III left-sided CRC, diagnosed and surgically treated in 2015-2017 were selected from the Netherlands Cancer Registry (n = 3286). Postoperative outcomes, short-term (30-, 60-, and 90-day) mortality and 3-year overall and relative survival were analyzed, stratified by surgical resection with PA versus EO. Propensity score matching (PSM) and multivariable logistic regression analysis were conducted. RESULTS: Patients with higher age, higher American Society of Anesthesiologists classification and higher tumor stage, a perforation, ileus or tumor located in the proximal rectum, and after open or converted surgery were more likely to receive EO. No difference in anastomotic leakage was seen in PA patients with or without defunctioning stoma (6.2% vs. 7.0%, p = 0.680). Postoperative hospital stay was longer (7.0 vs. 6.0 days, p < 0.0001) and more often prolonged (19% vs. 13%, p = 0.03) in EO patients. Sixty-day mortality (2.9% vs. 6.4%, p < 0.0001), 90-day mortality (3.4% vs. 7.7%, p < 0.0001), and crude 3-year survival (81.2% vs. 58.7%, p < 0.0001) were significantly higher in EO patients, remaining significant after multivariable and PSM analysis. CONCLUSION: There are significant differences between elderly patients after left-sided CRC surgery with PA versus EO in terms of postoperative length of stay, short-term survival, 3-year overall survival, and relative survival at disadvantage of EO patients. This information could be important for decision making regarding surgical treatment in the elderly.

Frailty is associated with in-hospital mortality in older hospitalised COVID-19 patients in the Netherlands: the COVID-OLD study.

BACKGROUND: During the first wave of the coronavirus disease 2019 (COVID-19) pandemic, older patients had an increased risk of hospitalisation and death. Reports on the association of frailty with poor outcome have been conflicting. OBJECTIVE: The aim of the present study was to investigate the independent association between frailty and in-hospital mortality in older hospitalised COVID-19 patients in the Netherlands. METHODS: This was a multicentre retrospective cohort study in 15 hospitals in the Netherlands, including all patients aged ≥70 years, who were hospitalised with clinically confirmed COVID-19 between February and May 2020. Data were collected on demographics, co-morbidity, disease severity and Clinical Frailty Scale (CFS). Primary outcome was in-hospital mortality. RESULTS: A total of 1,376 patients were included (median age 78 years (interquartile range 74-84), 60% male). In total, 499 (38%) patients died during hospital admission. Parameters indicating presence of frailty (CFS 6-9) were associated with more co-morbidities, shorter symptom duration upon presentation (median 4 versus 7 days), lower oxygen demand and lower levels of C-reactive protein. In multivariable analyses, the CFS was independently associated with in-hospital mortality: compared with patients with CFS 1-3, patients with CFS 4-5 had a two times higher risk (odds ratio (OR) 2.0 (95% confidence interval (CI) 1.3-3.0)) and patients with CFS 6-9 had a three times higher risk of in-hospital mortality (OR 2.8 (95% CI 1.8-4.3)). CONCLUSIONS: The in-hospital mortality of older hospitalised COVID-19 patients in the Netherlands was 38%. Frailty was independently associated with higher in-hospital mortality, even though COVID-19 patients with frailty presented earlier to the hospital with less severe symptoms.

Negligible epimuscular myofascial force transmission between the human rectus femoris and vastus lateralis muscles in passive conditions.

PURPOSE: There have been contradictory reports of the effects of epimuscular myofascial force transmission in humans. This study investigated the transmission of myofascial force to the human vastus lateralis muscle by determining whether vastus lateralis slack angle changed with hip angle. Since the distance between the origin and insertion of the vastus lateralis muscle does not change when hip angle changes, any change in vastus lateralis slack angle with hip position can be attributed to epimuscular myofascial force transmission. METHODS: Nineteen young adults were tested in hip flexed ([Formula: see text]) and neutral ([Formula: see text]) positions. Ultrasound images of the vastus lateralis muscle were obtained as the knee was passively flexed at [Formula: see text]/s. The knee angle at which vastus lateralis muscle fascicles began to lengthen was used to identify muscle slack angle. RESULTS: Overall, there was a negligible effect of hip position on vastus lateralis slack angle ([Formula: see text] [[Formula: see text] to 1.9]; mean [95% confidence interval]). However, a small and variable effect was noted in 3/19 participants. CONCLUSION: This result indicates that, over the range of joint angles tested here, there is little or no epimuscular myofascial force transmission between the vastus lateralis muscle and neighbouring bi-articular structures under passive conditions. More broadly, this result provides additional evidence that epimuscular myofascial force transmission tends to be small and variable under passive conditions in healthy human muscle.

Changes in muscle-tendon unit length-force characteristics following experimentally induced photothrombotic stroke cannot be explained by changes in muscle belly structure.

PURPOSE: The aim of this study was to assess the effects of experimentally induced photothrombotic stroke on structural and mechanical properties of rat m. flexor carpi ulnaris. METHODS: Two groups of Young-adult male Sprague-Dawley rats were measured: stroke (n = 9) and control (n = 7). Photothrombotic stroke was induced in the forelimb region of the primary sensorimotor cortex. Four weeks later, muscle-tendon unit and muscle belly length-force characteristics of the m. flexor carpi ulnaris, mechanical interaction with the neighbouring m. palmaris longus, the number of sarcomeres in series within muscle fibres, and the physiological cross-sectional area were measured. RESULTS: Stroke resulted in higher force and stiffness of the m. flexor carpi ulnaris at optimum muscle-tendon unit length, but only for the passive conditions. Stroke did not alter the length-force characteristics of m. flexor carpi ulnaris muscle belly, morphological characteristics, and the extent of mechanical interaction with m. palmaris longus muscle. CONCLUSION: The higher passive force and passive stiffness at the muscle-tendon unit level in the absence of changes in structural and mechanical characteristics of the muscle belly indicates that the experimentally induced stroke resulted in an increased stiffness of the tendon.

Modulation of soleus muscle H-reflexes and ankle muscle co-contraction with surface compliance during unipedal balancing in young and older adults.

This study aimed to assess modulation of lower leg muscle reflex excitability and co-contraction during unipedal balancing on compliant surfaces in young and older adults. Twenty healthy adults (ten aged 18-30 years and ten aged 65-80 years) were recruited. Soleus muscle H-reflexes were elicited by electrical stimulation of the tibial nerve, while participants stood unipedally on a robot-controlled balance platform, simulating different levels of surface compliance. In addition, electromyographic data (EMG) of soleus (SOL), tibialis anterior (TA), and peroneus longus (PL) and full-body 3D kinematic data were collected. The mean absolute center of mass velocity was determined as a measure of balance performance. Soleus H-reflex data were analyzed in terms of the amplitude related to the M wave and the background EMG activity 100 ms prior to the stimulation. The relative duration of co-contraction was calculated for soleus and tibialis anterior, as well as for peroneus longus and tibialis anterior. Center of mass velocity was significantly higher in older adults compared to young adults ([Formula: see text] and increased with increasing surface compliance in both groups ([Formula: see text]. The soleus H-reflex gain decreased with surface compliance in young adults [Formula: see text], while co-contraction increased [Formula: see text]. Older adults did not show such modulations, but showed overall lower H-reflex gains [Formula: see text] and higher co-contraction than young adults [Formula: see text]. These results suggest an overall shift in balance control from the spinal level to supraspinal levels in older adults, which also occurred in young adults when balancing at more compliant surfaces.

Neuromuscular control during gait in people with haemophilic arthropathy.

INTRODUCTION: Effects of haemophilic arthropathy on neuromuscular control during gait are currently unknown. AIMS: (a) To assess how haemophilic arthropathy affects the complexity of neuromuscular control during gait; (b) To investigate the relationship between complexity of neuromuscular control and joint impairment. METHODS: Thirteen control subjects (CG) walked overground at their preferred and a slow velocity and thirteen people with haemophilic arthropathy (PWHA) walking at their preferred velocity. Surface electromyography (EMG) was collected from eleven leg muscles. Electromyography variance explained by muscle synergies (sets of co-activated muscles that can be recruited by a single signal) was calculated by the total variance accounted (tVAF). Three measures were used to evaluate complexity of neuromuscular control: (a) the number of synergies required for tVAF > 90%, (b) tVAF as a function of the number of muscle synergies, and (c) the dynamic motor control index (Walk-DMC). Impairment of ankle and knee joints was determined by the Haemophilia Joint Health Score (HJHS). RESULTS: The same number of the muscle synergies was found for each group (P > 0.05). For both walking velocities tested, tVAF1 was higher in PHWA (P < 0.05). The Walk-DMC of PWHA was lower than that of the CG for both walking velocities (P < 0.05). For PWHA, no significant correlation was found between HJHS (sum knee and ankle) and Walk-DMC index (r = -0.32, P = 0.28). CONCLUSIONS: These results indicate differences between PWHA and CG in the neuromuscular control of gait. The Walk-DMC and tVAF1 may be useful measures to assess changes in neuromuscular control in response to treatment.

Single finger movements in the aging hand: changes in finger independence, muscle activation patterns and tendon displacement in older adults.

With aging, hand mobility and manual dexterity decline, even under healthy circumstances. To assess how aging affects finger movement control, we compared elderly and young subjects with respect to (1) finger movement independence, (2) neural control of extrinsic finger muscles and (3) finger tendon displacements during single finger flexion. In twelve healthy older (age 68-84) and nine young (age 22-29) subjects, finger kinematics were measured to assess finger movement enslaving and the range of independent finger movement. Muscle activation was assessed using a multi-channel electrode grid placed over the flexor digitorum superficialis (FDS) and the extensor digitorum (ED). FDS tendon displacements of the index, middle and ring fingers were measured using ultrasound. In older subjects compared to the younger subjects, we found: (1) increased enslaving of the middle finger during index finger flexion (young: 25.6 ± 12.4%, elderly: 47.0 ± 25.1%; p = 0.018), (2) a lower range of independent movement of the index finger (youngmiddle = 74.0%, elderlymiddle: 45.9%; p < 0.001), (3) a more evenly distributed muscle activation pattern over the finger-specific FDS and ED muscle regions and (4) a lower slope at the beginning of the finger movement to tendon displacement relationship, presenting a distinct period with little to no tendon displacement. Our study indicates that primarily the movement independence of the index finger is affected by aging. This can partly be attributed to a muscle activation pattern that is more evenly distributed over the finger-specific FDS and ED muscle regions in the elderly.