Effect of strength and speed of torque development on balance recovery with the ankle strategy
ABSTRACT In the event of an unexpected disturbance to balance, the ability to recover a stable upright stance should depend not only on the magnitude of torque that can be generated by contraction of muscles spanning the lower extremity joints but also on how quickly these torques can be developed. In the present study, we used a combination of experimental and mathematical models of balance recovery by sway (feet in place responses) to test this hypothesis. Twenty-three young subjects participated in experiments in which they were supported in an inclined standing position by a horizontal tether and instructed to recover balance by contracting only their ankle muscles. The maximum lean angle where they could recover balance without release of the tether (static recovery limit) averaged 14.9 +/- 1.4 degrees (mean +/- SD). The maximum initial lean angle where they could recover balance after the tether was unexpectedly released and the ankles were initially relaxed (dynamic recovery limit) averaged 5.9 +/- 1.1 degrees, or 60 +/- 11% smaller than the static recovery limit. Peak ankle torque did not differ significantly between the two conditions (and averaged 116 +/- 32 Nm), indicating the strong effect on recovery ability of latencies in the onset and subsequent rates of torque generation (which averaged 99 +/- 13 ms and 372 +/- 267 N. m/s, respectively). Additional experiments indicated that dynamic recovery limits increased 11 +/- 14% with increases in the baseline ankle torques prior to release (from an average value of 31 +/- 18 to 54 +/- 24 N. m). These trends are in agreement with predictions from a computer simulation based on an inverted pendulum model, which illustrate the specific combinations of baseline ankle torque, rate of torque generation, and peak ankle torque that are required to attain target recovery limits.
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- "The time to reach peak torque is another important parameter that represents the responsiveness of the body to a disturbance (Thelen et al., 1996, 1997). When a delay in response time to an imbalance occurs, the risk of falling is increased (Thelen et al., 1996; Robinovitch et al., 2002). Our findings demonstrated that the time to reach peak torque in knee flexion and ankle dorsiflexion in younger adults was shorter than all older participants regardless of "
ABSTRACT: This study aimed to evaluate the motor response time and ability to develop joint torque at the knee and ankle in older women with and without a history of falls, in addition to investigating the effect of aging on these capacities. We assessed 18 young females, 21 older female fallers and 22 older female non-fallers. The peak torque, rate of torque development, rate of electromyography (EMG) rise, reaction time, premotor time and motor time were obtained through a dynamometric assessment and simultaneous electromyography. Surface EMGs of the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), gastrocnemius lateralis (GL) and tibialis anterior (TA) muscles were recorded. Knee extension and flexion peak torques were lower in older fallers than in non-fallers. Knee extension and flexion and ankle plantarflexion and dorsiflexion peak torques were lower in both older groups than in the younger group. The rate of EMG rise of the BF and the motor time of the TA were lower and higher, respectively, in older fallers than in the younger adults. The time to reach peak torque in knee extension/flexion and ankle plantarflexion/ dorsiflexion and the motor times of the RF, VL, BF and GL were higher in both older groups than in the younger groups. The motor time of the TA during ankle dorsiflexion and the knee extension peak torque were the major predictors of falls in older women, accounting for approximately 28% of the number of falls. Thus, these results further reveal the biomechanical parameters that affect the risk of falls and provide initial findings to support the prescription of exercises in fall prevention programs.Journal of Electromyography and Kinesiology 06/2013; · 1.65 Impact Factor
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- "Oliveira et al.  calculated peak RTD during isokinetic muscle actions at 60 and 180 • ·s −1 by calculating the peak slope of the entire moment-time curve during the isokinetic muscle action and reported an increase in RTD at 60 • ·s −1 and 180 • ·s −1 after a single habituation session. Given the results of the present study, however, conclusions made based on isokinetic RTD data in these previous studies   may lack Fig. 3. iEMG during voluntary isokinetic muscle actions in 10 ms epochs (open circles) and integrated M-wave area of evoked isokinetic muscle actions (closed circle) at 60 • ·s −1 . The vertical line at zero represents the onset of moment and the area to the left of this line may be considered the electromechanical delay. "
ABSTRACT: Background: The rate of torque development (RTD) and the rate of velocity development (RVD) have previously been described as related; however, a direct comparison has not been performed. Objective: The purposes of this study were to compare voluntary and evoked RVD and RTD during the same maximal isokinetic leg extensions muscle actions and to indirectly explore the influence of motor unit discharge frequency on these variables. Methods: Sixteen men completed three maximal voluntary and three maximal evoked isokinetic leg extension muscle actions at 60°·s-1. Peak RVD, general RVD, peak RTD, and electromechanical delay (EMD) were calculated from the voluntary and evoked muscle actions. Voluntary and evoked RTD and RVD were also calculated for each 10 ms epoch up to 200 ms of the muscle actions. Results: There was no interaction between voluntary and evoked RVD across time (p=0.12), but there was an interaction for RTD (p<0.01). However, peak RTD occurred prior to the isokinetic load range. Peak RTD (p<0.001), peak RVD (p< 0.01), general RVD (p< 0.01), isokinetic load range (p<0.001), EMD (p<0.001), and PT (p<0.001) were greater for voluntary than evoked muscle actions, which was expected due to the influence of voluntary motor unit firing rates. Conclusions: Overall, these results suggested that the calculation of RTD during the acceleration phase of an isokinetic muscle action may not be valid due to the unknown load and increasing velocity. Furthermore, the RVD may be influenced by motor unit firing rate, but to a lesser extent than RTD.Isokinetics and exercise science 01/2013; 21(3):253-261. DOI:10.3233/IES-130504 · 0.49 Impact Factor
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- "Elderly individuals are less able to handle sudden , unexpected changes (Pijnappels et al. 2005; Karamanidis and Arampatzis 2007; Bierbaum et al. 2010). Reasons for the decreased ability to recover balance are the age-related reduction in muscle strength and tendon stiffness (Grabiner et al. 2005; Karamanidis et al. 2008), the delayed generation of propulsive ground reaction forces and joint torques (Robinovitch et al. 2002; Pijnappels et al. 2005; Tseng et al. 2009), and the lower muscular contraction velocities (Hortobágyi et al. 1995; Thelen et al. 1997). If the postural system is unstable, stepping strategies seem to be less successful for the elderly due to reductions in step length and speed (Wojcik et al. 2001; Karamanidis et al. 2008; Bierbaum et al. 2010). "
ABSTRACT: Unexpected changes during gait challenge elderly individuals to a greater degree than young adults. However, the adaptive potential of elderly seems to be retained, and therefore, the training of the mechanisms of dynamic stability as well as muscle strength training may improve the dynamic stability after unexpected perturbations. Thirty-eight subjects (65-75 years) participated in the study, divided into two experimental groups (stability training group, ST, n = 14 and mixed training group, MT, n = 14) and a control group (CG, n = 10). Both experimental groups performed exercises which focused on the mechanisms of dynamic stability. Additionally, the MT group executed a training to improve muscle strength. Session volume and duration were equal for both groups (14 weeks, twice a week, ~1.5 h per session). Pre- and post-intervention, subjects performed a gait protocol with an induced unexpected perturbation. Post-intervention, the margin of stability was significantly increased after the unexpected perturbation in the ST group, indicating an improvement in stability state (pre, -30.3 ± 5.9 cm; post, -24.1 ± 5.2 cm). Further, both intervention groups increased their base of support after the intervention to regain balance after gait perturbation, whereas only the ST group showed a statistically significant improvement (ST(pre), 90.9 ± 6.6 cm, ST(post), 98.2 ± 8.5 cm; MT(pre), 91.4 ± 6.2 cm; MT(post), 97.9 ± 12.7 cm). The CG showed no differences between pre- and post-measurements. The exercise of the mechanisms of dynamic stability led to a better application of these mechanisms after an unexpected perturbation during gait. We suggest that the repeated exercise of the mechanisms of dynamic stability contributes to significant improvements in postural stability. Additional strength training for healthy elderly individuals, however, shows no further effect on the ability to recover balance after unexpected perturbations during gait.Age 10/2012; 35(5). DOI:10.1007/s11357-012-9481-z · 3.45 Impact Factor