The Relevance of Dual Tasking for Improving Trunk Muscle Endurance After Back Surgery.

OBJECTIVE: To determine the effect of dual tasking on trunk muscle endurance in patients after lumbar diskectomy. DESIGN: Cross-sectional study. SETTING: Rehabilitation hospital setting. PARTICIPANTS: Individuals (N=14) undergoing primary lumbar diskectomy. INTERVENTION: Using a randomized design on 2 separate days, muscle endurance was evaluated during prone bridging and Biering-Sorensen tests. Each test was randomly performed under 2 cognitive conditions: single task without cognitive condition and self-regulated dual task (ie, mathematical task). MAIN OUTCOME MEASURES: The primary outcomes were time to failure and pain assessed by the visual analog scale from 0 to 100 mm. The secondary outcomes were kinesiophobia assessed by the Tampa Scale and disability assessed by the Oswestry Disability Index. Associations were tested using a repeated measures analysis of variance with relevant interaction test. RESULTS: A significant interaction between condition, endurance tests, and kinesiophobia (P=.005) was found. The post hoc comparison showed positive effects between cognitive conditions in both endurance tests (prone bridging test: mean difference, 15.7s; 95% confidence interval [CI], 7.5-24s; P=.001; Biering-Sorensen test: mean difference, 7.9s; 95% CI, 1.9-14s; P=.014). The linear regression analysis between the Tampa Scale for Kinesiophobia and the difference of time to failure between cognitive conditions showed a positive correlation only during the Biering-Sorensen test (r=0.80; P=.001). CONCLUSIONS: A self-regulated dual task increases trunk muscle endurance in patients after lumbar diskectomy. The results suggest that the difference observed in time to failure between the single task and dual task is associated with fear avoidance, especially during back extension. This strategy seems especially relevant for patients with high levels of fear avoidance and may be used to improve trunk muscle endurance.

Effects of dual-task demands on the complexity and task performance of submaximal isometric handgrip force control.

PURPOSE: To determine the effect of cognitive-motor dual-task load on temporal structure irregularity (complexity) of motor output and task performance of submaximal isometric contractions. METHODS: Twelve young, sedentary subjects performed handgrip isometric contractions until failure at 50% of maximal voluntary contraction under mathematical self-regulated dual-task (own pace; SDT), regulated dual-task (imposed pace; RDT), and control. Force signal complexity was calculated by sample entropy at the initial, middle, and final thirds. Task performance was assessed by muscle fatigue (time to failure and rate of median frequency of the radial flexor of the carpus), force and math task error, and self-perceived difficulty. RESULTS: Only RDT decreased complexity with respect to control (17.4% ± 12.6%, p = 0.005), all conditions decreased complexity by the final third (Control: 52.8% ± 18.7%, p < 0.001; SDT: 41.1% ± 32.1%, p = 0.003; RDT: 19.1% ± 21.9%, p = 0.035). Conditions did not affect time to failure, and only RDT decreased the rate of median frequency (0.1%/s ± 0.1%/s, p = 0.020). Inferior force error rate was increased by conditions (SDT: 1.5% ± 0.8%, p < 0.001; RDT: 2% ± 1.5%, p = 0.002). Math error was only augmented by RDT (from 9.9 ± 6.7 to 51.7 ± 18.8, p < 0.001), categorized as "very hard" in 85.7% of participants (p = 0.015). CONCLUSION: Only the RDT condition reduced complexity and neuromuscular fatigue while increasing force error rate of the handgrip's motor output, without affecting time to failure. A highly demanding dual-task may become a strategy to modify the organization of the hand force motor output, which may contribute to its motor adaptations.

Effects of performing dual tasks on postural sway and postural control complexity in people with haemophilic arthropathy.

INTRODUCTION: People with haemophilic arthropathy (PWHA) have impairments in postural control. However, little is known about the effects of demanding conditions, including the unipedal stance and dual tasks, on postural control in PWHA. AIM: Determine the effects of performing dual tasks while in the one-leg stance on postural sway and postural control complexity in PWHA vs. healthy active (HAG) and non-active (HNAG) groups of individuals. METHODS: Fifteen PWHA and 34 healthy subjects (18 active and 16 non-active) were recruited. Vertical (V), mediolateral (ML) and anteroposterior (AP) centre of mass signals were acquired using a 3-axis accelerometer placed at the L3/L4 vertebrae of subjects as they performed the one-leg stance under single and dual-task conditions. Sway balance and the complexity of postural control were studied via root mean square (RMS) acceleration and sample entropy, respectively. Increased complexity of postural sway was attributed to increased automatism of postural control. RESULTS: RMS values for PWHA were higher than HAG under both conditions for the V and ML axes, and higher than HNAG under the dual-task condition for the ML axis. Sample entropy was lower in PWHA than healthy individuals under the dual-task condition for V and ML axes, and the single-task condition for the ML axis (P < .05). CONCLUSION: PWHA had poorer postural sway and decreased postural control complexity when performing a one-leg stance than healthy people, especially when the dual-task condition was applied. These results may help to design new approaches to assess and improve postural control in PWHA.

Effect of neuromuscular electrical stimulation frequency on postprandial glycemia, current-related discomfort, and muscle soreness. A crossover study.

Consensus is lacking regarding optimal neuromuscular electrical stimulation (NMES) parameters for postprandial glycemic control. Therefore, the aim of this study was to determine the NMES frequency inducing the greatest hypoglycemic effect in healthy individuals. The secondary aim was to compare current-related discomfort and muscle soreness between different frequencies. We conducted an experimental clinical study with a randomized crossover design. Sixteen healthy and sedentary participants received NMES for 20 min at 5, 10, or 50 Hz (pulse duration: 400 µs, on-off ratio: 4:12 s) following a standardized meal. Glycemia, discomfort, and muscle soreness during and after NMES were compared between conditions. Five-hertz NMES generated a significant hypoglycemic effect, contrary to 10 Hz and 50 Hz. Ten-hertz and 50-Hz NMES resulted respectively in lower current-related discomfort and greater muscle soreness compared with the other frequencies. Women reported higher discomfort than men. These findings contribute towards the possibility of more efficient long-term NMES treatments in terms of glycemic response and patient tolerance.