Neuromuscular Characteristics and Physical Function in Participants with Parkinson’s Disease

PURPOSE: This study aimed to investigate the level of physical function, lower body strength, and muscle activation during various types of muscle contraction in participants with and without Parkinson’s disease (PD).METHODS: Twelve participants with PD (mean age=63.17±6.24 years) and 12 age- and sex-matched healthy adults (mean age = 58.67±6.39 years) were recruited. An isokinetic dynamometer was used to measure the length- and velocity-dependent maximum voluntary force and the rate of torque development (RTD) of the knee extensor muscles. Muscle activation of the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles of both legs was examined using surface electromyography. The 6-minute walk test, chair stand test, timed up-and-go test, sit-and-reach test, and back-scratch test were performed to assess physical function.RESULTS: Compared to healthy individuals, participants with PD showed significantly lower maximum voluntary force and RTD (<i>p</i><.05), performed fewer repetitions in the chair stand test (11.64±1.75 vs. 17.08±2.27, <i>p</i><.001), were slower in the timed up-andgo test (8.36±1.42 vs. 5.65±1.07, <i>p</i><.001), and walked shorter distances in the 6-minute walk test (424.17±65.97 vs. 539.47±63.18, <i>p</i><.001). However, activation of the three different muscles during isometric and isokinetic muscle contraction was not different between participants with and without PD.CONCLUSIONS: Preserved muscle activation and significantly lower muscle strength during various types of muscle contractions may suggest lower muscle strength and efficiency. The lower physical function seen in participants with mild PD could be due to disease and low physical activity-related muscle atrophy rather than lower muscle activation.

Comparison of single and multiple joint muscle functions and neural drive of trained athletes and untrained individuals

BACKGROUND: There is insufficient knowledge about the rate of force development (RFD) characteristics over both single and multiple joint movements and the electromechanical delay (EMD) values obtained in athletes and untrained individuals. OBJECTIVE: To compare single and multiple joint functions and the neural drive of trained athletes and untrained individuals. METHODS: Eight trained athletes and 10 untrained individuals voluntarily participated to the study. The neuromuscular performance was assessed during explosive and maximum voluntary isometric contractions during leg press and knee extension related to single and multiple joint. Explosive force and surface electromyography of eight superficial lower limb muscles were measured in five 50-ms time windows from their onset, and normalized to peak force and electromyography activity at maximum voluntary force, respectively. The EMD was determined from explosive voluntary contractions (EVC’s). RESULTS: The results showed that there were significant differences in absolute forces during knee extension maximum voluntary force and EVC’s (p< 0.01) while trained athletes achieved greater relative forces than untrained individuals of EVC at all five time points (p< 0.05). CONCLUSIONS: The differences in explosive performance between trained athletes and untrained individuals in both movements may be explained by different levels of muscle activation within groups, attributed to variation in biarticular muscle function over both activities.

Dorsiflexion But Not Plantarflexion Force Declines At Lower Foot Skin Temperatures

Background/Aims Muscle maximum voluntary force declines at skin temperature <20°C, attributed to cold muscle, however large muscle deep fibres remain at >20°C. Large muscle maximum voluntary force decline is comparable to that in small superficial muscle where muscle temperature remains close to skin temperature. Therefore, factors in addition to temperature may contribute to large muscle maximum voluntary force decline. This study compares the effects of foot and/or shank skin temperature on dorsiflexion and plantarflexion maximum voluntary force with the hypotheses that: dorsiflexion maximum voluntary force>plantarflexion maximum voluntary force decline at lower skin temperature; and, plantarflexion and dorsiflexion maximum voluntary force will decline at lower shank skin temperature independent of foot skin temperature. Methods A total of 24 adults (15 females, 9 males, 29 ± 11.8 years, 170.1 ± 8.0 cm, 66.9 ± 9.3 kg [mean ± standard deviation]) gave informed consent to participate on three visits – cooling/warming of: foot only; foot and shank; and shank only. Foot and/or shank temperature was adjusted using Cryocuff™ sleeves filled with ~45°C or ~4°C water. Temperature, taken before each maximum voluntary force set, was monitored through thermocouples placed on the limb. Plantarflexion and dorsiflexion maximum voluntary force were measured with a KinCom isokinetic dynamometer, with subjects seated on a plinth with knee fully extended and neutral ankle. A general mixed model was used to evaluate the effects of skin temperature on maximum voluntary force. Fixed effects were skin temperature and condition, with subject as a random effect. The skin temperature*condition interaction was also modelled. P-values were obtained by likelihood ratio tests. Results Foot skin temperature <18.5°C resulted in a 10% (χ2(1)=5.479, P=0.019) dorsiflexion maximum voluntary force decline, with a skin temperature*condition interaction (χ2(2)=11.031, P=0.004), this decline was 12% (χ2(1)=13.18, P=0.0003) in foot only and 8% (χ2(1)=4.675, P=0.031) in foot and shank. Leg skin temperature did not affect (χ2(1)=2.849, P=0.091) dorsiflexion maximum voluntary force. Plantarflexion maximum voluntary force did not change with foot skin temperature (χ2(1)=0.04, P=0.841) or leg skin temperature (χ2(1)=0.082, P=0.929). Conclusions Dorsiflexion maximum voluntary force declines at lower foot skin temperature independently of shank skin temperature, whereas plantarflexion maximum voluntary force is unaffected by skin temperature, possibly because in this protocol the shank was insufficiently cooled. Therefore factors other than direct muscle cooling must contribute to dorsiflexion maximum voluntary force decline. One theory is a rightward shift in the force-length relationship, due to stiffer tendon, could result in dorsiflexions operating in the descending limb of the force-length relationship. This warrants further investigation.

NemaFlex: a microfluidics-based technology for standardized measurement of muscular strength of C. elegans

NemaFlex measures a behavior- and gait-independent measure of C. elegans strength analogous to maximum voluntary force in humans.

Grip Type Alters Maximal Pinch Forces in Syringe Use

Objective: The purpose of this study was to determine maximum forces during syringe use for different grips found in the field. Background: Prolonged syringe use in chemotherapy drug delivery is associated with pain and injury in nurses and technicians. Method: Twenty healthy female hospital workers generated isometric maximum voluntary force using a 30 cc syringe with four pinch grips (chuck, chuck variation, thenar, two-handed). Both dominant and nondominant hands were used with the syringe plunger fixed in wide (8.3 cm) and narrow (2.5 cm) grip spans. Participants were encouraged to position the apparatus in the most comfortable position and exert a maximal effort for 5 seconds. Results: Significant interaction effects were found: Grip Span × Pinch Type, Hand × Pinch Type, and Grip Span × Hand × Pinch Type ( p < .05). The results demonstrated that the thenar (103.6 ± 22.9 N) and two-handed (104.7 ± 17.1 N) pinches produced the highest forces. Conclusion: Thenar and two-handed pinch grips may be the preferred pinch type to lower the relative efforts required to use a syringe and may be one strategy to assist with reduction of musculoskeletal disorder risk associated with syringe use. Application: Determining maximal syringe press forces allows workers and ergonomists to develop better strategies for managing the cumulative loads during drug delivery and mixing.

Preliminary findings of finger independency and visual force control in children with DCD

<p>Finger independency and visual force control were studied in children with DCD. Five children, 9 to10 years of age, diagnosed with DCD and five age-matched typically developing children were asked to perform two isometric tasks, maximum voluntary force production (MVF) and visual force control (VFC), in seven different finger conditions [Index (I), Middle (M), Ring (R), Little (L) IM, IMR, and IMRL]. For the VFC tasks, the participants were asked to continuously control their finger forces at 20% of the MVF. To examine finger force independency, maximum voluntary force (MVF), force enslaving (FE) and force sharing (FS) values were computed. To analyze the ability of children with DCD to visually control their finger forces, the following performance measures were calculated: rate of force change, initial overshoot, coefficient of variation (CV), root mean square error (RMSe), and inter-trial variability. The results from the MVF task showed that children with DCD as compared with TD children (a) produced similar levels of maximum finger force; (b) demonstrated less finger independency; (c) had similar finger-force sharing patterns. In addition, from the VFC task we found (d) larger performance errors in children with DCD; (e) and lower inter-trial consistency as compared to their TD peers. Our preliminary findings suggest that the impairments in manipulative skills often observed in children with DCD during everyday activities may be related to deficits in finger independency. Additionally we found that children with DCD do not have difficulties in reducing the number of joint/muscle-level degrees of freedom in order to achieve a common motor task.</p>

Preliminary findings of finger independency and visual force control in children with DCD

To examine finger force independency, maximum voluntary force (MVF), force enslaving (FE) and force sharing (FS) values were computed. To analyze the ability of children with DCD to visually control their finger forces, the following performance measures were calculated: rate of force change, initial overshoot, coefficient of variation (CV), root mean square error (RMSe), and inter-trial variability. The results from the MVF task showed that children with DCD as compared with TD children (a) produced similar levels of maximum finger force; (b) demonstrated less finger independency;(c) had similar finger-force sharing patterns. In addition, from the VFC task we found (d) larger performance errors in children with DCD;(e) and lower inter-trial consistency as compared to their TD peers.Our preliminary findings suggest that the impairments in manipulative skills often observed in children with DCD during everyday activities may be related to deficits in finger independency.Additionally we found that children with DCD do not have difficulties in reducing the number of joint/muscle-level degrees of freedom in order to achieve a common motor task.

Muscle-tendon unit stiffness does not independently affect voluntary explosive force production or muscle intrinsic contractile properties

This study examined the relationship of muscle-tendon unit (MTU) stiffness and explosive force production during voluntary and evoked contractions of the knee extensors. Thirty-four untrained participants performed a series of explosive voluntary and electrically evoked (octets (8 pulses, 300 Hz) via femoral nerve stimulation) isometric contractions. Maximum voluntary force (MVF) was assessed during maximum voluntary contractions. Explosive force production was assessed as the time taken, from force onset (0 N), to achieve specific levels of absolute (25–300 N) and relative force (5%–75% MVF) during the explosive contractions. Ultrasonic images of the vastus lateralis were recorded during 10-s ramp contractions to assess MTU stiffness, which was expressed in absolute (N·mm−1) and relative (to MVF and resting tendon-aponeurosis length) terms. Bivariate correlations suggested that absolute MTU stiffness was associated with voluntary explosive force (time to achieve 150–300 N: r = –0.35 to –0.54, P < 0.05). However, no relationships between stiffness and voluntary explosive force were observed when the influence of MVF was removed, either via partial correlations of absolute values (P ≥ 0.49) or considering relative values (P ≥ 0.14). Similarly, absolute MTU stiffness was related to explosive force during evoked octet contractions (r = –0.41 to –0.64, P < 0.05), but these correlations were no longer present when accounting for the influence of MVF (P ≥ 0.15). Therefore, once maximum strength was considered, MTU stiffness had no independent relationship with voluntary explosive force production or the evoked capacity for explosive force.

The Influence of Task Frequency and Force Direction on Psychophysically Acceptable Forces in the Context of the Biomechanically Weakest Links

This study examined the influence of frequency and direction of force application on psychophysically acceptable forces for simulated work tasks. Fifteen male participants exerted psychophysically acceptable forces on a force transducer at 1, 3, or 5 repetitions per minute by performing both a downward press and a pull toward the body. These exertions were shown previously to be strength and balance limited, respectively. Workers chose acceptable forces at a lower percentage of their maximum voluntary force capacity during downward (strength-limited) exertions than during pulling (balance-limited) exertions at all frequencies (4% to 11%, P = .035). Frequency modulated acceptable hand force only during downward exertions, where forces at five repetitions per minute were 13% less (P = .005) than those at one exertion per minute. This study provides insight into the relationship between biomechanically limiting factors and the selection of acceptable forces for unilateral manual tasks.