Effects of current amplitude and pulse duration modulation on neuromuscular fatigue during repetitive electrical stimulation

Functional electrical stimulation (FES) has been used to enhance function and prevent muscle atrophy in people with spinal cord injury (SCI). In this study, we examined the effect of two different stimulation parameter sets on FES-induced muscle fatigue in 10 healthy individuals. Methods: 3 FES protocols were applied to the knee extensor muscle group of participants. The experimental protocols were as follows: practice session, test session 1 and test session 2. Subjects were trained to perform the MVIC test, and their MVIC was measured in the practice session. A long pulse duration (1000μs) and a current amplitude set to evoke 25% MVIC at 30 Hz was applied on subject's thigh for 2 minutes in test session 1. The protocol for test session 2 was identical to the test session 1 with the exception of a different pulse shape. A short pulse duration (200μs) and a current amplitude set to evoke 25% MVIC was used in test session 2. The percentage decline in peak force, the recovery rate during rest-periods, and self-reported pain were compared between the two FES parameter sets in both test sessions. Results: Percent muscle fatigue was significantly lower for the parameter set with long pulse duration (1000μs) and low current amplitude (LL) than for the stimulation parameter set with short pulse duration (200μs) and high current amplitude (SH). The reduction of peak force between the first and last peaks was significantly lower in the LL condition than in the SH condition. Pain scores were significantly lower for the LL than for the SH. Conclusion: The use of LL reduced the occurrence of muscle fatigue and pain compared to the use of SH. These results suggest that stimulation with LL may help reduce muscle fatigue during FES application.Kinesiology and Health Educatio

Differences in Bone Mineral Density at the Femoral Neck and Lumbar Regions across Female Soccer Players, Olympic Lifters and Power Lifters

Power lifting can improve total body bone mineral density (BMD), but improvements in the regions most susceptible to injury (femoral neck and lumbar vertebrae) have not been demonstrated. Soccer players, who engage in odd-impact loading, have greater BMD at the femoral neck than sedentary controls. Olympic lifting involves both high- and odd-impact loading at the femoral neck and lumbar regions, but comparisons in BMD across sport-specific athletes have not yet been made. PURPOSE: To examine differences in total BMD and BMD at the femoral neck and lumbar vertebrae between female power lifters (PL), Olympic lifters (OL), soccer players (SP) and recreationally active individuals (RA). METHODS: Thirty-seven females participated in this study: 10 PL, 8 OL, 8 SP, and 11 RA (mean age = 24.5 ± 7.9 years). Total BMD, BMD at lumbar vertebrae L1-L4, and BMD at the femoral neck of the dominant leg were measured along with body composition (total fat mass, lean mass, and percent body fat) with dual-energy x-ray absorptiometry. Body composition components were compared across groups with a one-way ANOVA. BMD measures were compared across groups with an ANCOVA with weight, height, and body mass index as covariates. Tukey’s tests were used for post-hoc analysis. Significance was accepted at P \u3c 0.05. RESULTS: All three athletic groups had greater total BMD than RA (1.071 ± 0.066 g∙cm-2). OL (1.306 ± 0.08 g∙cm-2) had greater total BMD than PL (1.071 ± 0.07 g∙cm-2), but it was not different than SP. At the femoral neck, OL (1.127 ± 0.09 g∙cm-2) and SP (1.212 ± 0.10 g∙cm-2) [but not PL (1.075 ± 0.16 g∙cm-2)] had greater BMD than RA (0.971 ± 0.99 g∙cm-2). BMD at the femoral neck was greater in SP than in PL, with no difference between OL and PL. At lumbar spine sites L2 – L4, there was no difference across the three athletic groups. OL and PL had a greater BMD than RA at L2-4, whereas SP had greater BMD than RA at only at L4. There was no difference across all groups at L1. CONCLUSION: Olympic lifting includes both high- and odd- impact movements in addition to high-force loading. Olympic lifters showed similar BMD at the femoral neck as soccer players and similar BMD in the lumbar spine as power lifters. Thus, Olympic lifting may have greater BMD effects in the two key regions that are susceptible to injury compared to sports that do not combine power and odd-impact training

Age-Related Differences in Kinematics, Kinetics, and Muscle Synergy Patterns Following a Sudden Gait Perturbation: Changes in Movement Strategies and Implications for Fall Prevention Rehabilitation

Falls in older adults are leading causes of fatal and non-fatal injuries, negatively impacting quality of life among those in this demographic. Most elderly falls occur due to unrecoverable limb collapse during balance control in the single-limb support (SLS) phase. To understand why older adults are more susceptible to falls than younger adults, we investigated age-related differences in lower limb kinematics, kinetics, and muscle synergy patterns during SLS, as well as their relationship to postural control strategies. Thirteen older and thirteen younger healthy adults were compared during the SLS phase of balance recovery following an unexpected surface drop perturbation. Compared to younger adults, older adults demonstrated (1) greater trunk flexion, (2) increased hip extension torque and reduced hip abduction torque of the perturbed leg, and (3) higher postural sway. Trunk flexion was correlated with a delayed latency to the start of lateral-to-medial displacement of center of mass from the perturbation onset. The group-specific muscle synergy revealed that older adults exhibited prominent activation of the hip extensors, while younger adults showed prominent activation of the hip abductors. These findings provide insights into targeted balance rehabilitation and indicate ways to improve postural stability and reduce falls in older adults

The influence of smoothness and speed of stand-to-sit movement on joint kinematics, kinetics, and muscle activation patterns

BackgroundStand-to-sit (StandTS) is an important daily activity widely used in rehabilitation settings to improve strength, postural stability, and mobility. Modifications in movement smoothness and speed significantly influence the kinematics, kinetics, and muscle activation patterns of the movement. Understanding the impact of StandTS speed and smoothness on movement control can provide valuable insights for designing effective and personalized rehabilitation training programs.Research questionHow do the smoothness and speed of StandTS movement affect joint kinematics, kinetics, muscle activation patterns, and postural stability during StandTS?MethodsTwelve healthy younger adults participated in this study. There were two StandTS conditions. In the reference condition, participants stood in an upright position with their feet positioned shoulder-width apart on the force plate. Upon receiving a visual cue, participants performed StandTS at their preferred speed. In the smooth condition, participants were instructed to perform StandTS as smoothly as possible, aiming to minimize contact pressure on the seat. Lower leg kinetics, kinematics, and coordination patterns of muscle activation during StandTS were measured: (1) angular displacement of the trunk, knee, and hip flexion; (2) knee and hip extensor eccentric work; (3) muscle synergy pattern derived from electromyography (EMG) activity of the leg muscles; and (4) postural sway in the anterior–posterior (A-P), medio-lateral (M-L), and vertical directions.ResultsCompared to the reference condition, the smooth condition demonstrated greater eccentric knee extensor flexion and increased joint work in both the knee and hip joints. Analysis of specific muscle synergy from EMG activity revealed a significant increase in the relative contribution of hip joint muscles during the smooth condition. Additionally, a negative correlation was observed between knee extensor and vertical postural sway, as well as hip extensor work and M-L postural sway.ConclusionSmooth StandTS facilitates enhanced knee eccentric control and increased joint work at both the hip and knee joints, along with increased involvement of hip joint muscles to effectively manage falling momentum during StandTS. Furthermore, the increased contributions of knee and hip joint work reduced postural sway in the vertical and M-L directions, respectively. These findings provide valuable insights for the development of targeted StandTS rehabilitation training

Effects of aging on muscle activation patterns and postural control during sit-to-stand and balance recovery from medio-lateral perturbations across different initial foot positions

We investigated the effects of initial foot position (IFP) on muscle activation patterns and postural control during sit-to-stand (STS) and balance recovery from medio-lateral (M-L) perturbations and how they are different between younger and older adults. In study 1, the effects of different symmetric and asymmetric IFPs on leg muscle activation patterns and balance during and after a STS were examined. A faster forward velocity of the body’s center of mass (CoM) was required in more anterior symmetric IFPs and the greater forward velocity of the body’s CoM caused more postural sway following completion of upright stance. In the one-third back non-dominant leg with two-thirds back dominant leg asymmetric IFP from a 90° knee flexion, the weight-bearing symmetry was not different from the symmetric IFPs and postural stability after STS was improved. In study 2, we investigated the effects of different IFPs and aging on muscle activation patterns and balance during and after a STS. We found that the trunk forward-tilt angle and hip extension torque during uprising were smaller in TO and Wide for both age groups. Postural sway and center of pressure sway area were smallest in TO after completion of uprising with no difference between age groups. Adductor longus and gluteus medius activity was also greater in TO, and older adults activated these muscles more than younger adults in this IFP. This study showed that smaller trunk flexion with greater activation of the hip ab/adductor muscles in TO can contribute to improving postural stability during the STS. Study 3 evaluated the effects of IFPs and aging on changes in muscle activation patterns, kinematics, and postural sway during standing balance recovery in response to unexpected sudden M-L ground perturbations. We observed that M-L standing balance recovery starts with a reflex response to control the body’s CoM position immediately. Although the fibularis longus activity at the ankle joint is smaller in older adults, toes-out IFP provides greater activation of the soleus and fibularis longus and smaller increments of postural sway following perturbations in both age groups. The findings from these series of studies show that IFPs change leg muscle activation patterns and kinematics during a balance recovery motion and influence balance maintenance. These findings are important for designing strength and balance exercise interventions for clinical populations to improve dynamic balance and prevent falls.Kinesiology and Health Educatio

A Preliminary Study on How Combining Internal and External Focus of Attention in a Movement Language Can Improve Movement Patterns

Background: Movement feedback is used to promote anatomically correct movement patterns. Two primary forms of movement feedback exist: verbal cues and visual cues. There is ongoing debate regarding which type of feedback yields superior effects for learning desired movements. This study investigated how a combination of visual and verbal cues improved shoulder stability in four arm movements, Biceps Curls, Reverse Flys, Rowing, and Shoulder Extensions. Methods: Twelve participants were allocated to three different conditions and instructed to perform four different arm movements: Condition 1 (no specific instructions), Condition 2 (image only), and Condition 3 (verbal cues and image). Measurements of acromioclavicular (AC) joint displacement, and electromyography (EMG) peak and burst duration were taken for each arm movement within each condition. Results: Condition 3 exhibited a significant reduction in AC displacement and prolonged EMG burst duration. Variations in EMG peak and burst duration across different arm movements were attributed to anticipated muscle activation specific to each movement. Conclusions: The combination of visual and verbal cues through the “reConnect Your Dots” movement language was found to improve scapular stabilization and associated muscle activation. This approach to movement patterns practice holds promise for injury rehabilitation and risk mitigation for future occurrences

Perturbation-Induced Protective Arm Responses: Effect of Age, Perturbation-Intensity, and Relationship with Stepping Stability: A Pilot Study

During balance recovery from slip perturbations, forward flexion (elevation) of the arms serves to counterbalance the posteriorly displaced center of mass (CoM). We aimed to investigate whether aging affects modulation of arm responses to various intensities of unpredictable slip perturbations and whether arm responses are related to compensatory stepping stability. Ten healthy young adults and ten healthy older adults participated. Participants were asked to react naturally to three randomly administered levels of slip-like surface perturbations (intensity 1 (7.75 m/s2), intensity 2 (12.00 m/s2) and intensity 3 (16.75 m/s2), which occurred by means of forward acceleration of the treadmill belt while standing. Kinematic data were collected using a motion capture system. Outcomes included arm elevation displacement, velocity, and margin of stability (MoS) of compensatory stepping. The results reveal no modulation of arm elevation velocity in older adults from perturbation intensity 1 to 2, whereas younger adults demonstrated progressive increases from intensity 1 to 2 to 3. At intensity 3, older adults demonstrated reduced maximal arm elevation velocity compared to younger adults (p = 0.02). The results in both groups combined reveal a positive correlation between maximal arm elevation velocity and first compensatory step MoS at intensity 3 (p = 0.01). Together, these findings indicate age-related decreases in arm response modulation and the association of arm elevation response with protective stepping stability, suggesting that fall prevention interventions may benefit from an emphasis on arm elevation velocity control in response to greater perturbation intensities

Age-related differences in lower limb muscle activation patterns and balance control strategies while walking over a compliant surface

Abstract Substantial evidence demonstrates that falls in older adults are leading causes of fatal and non-fatal injuries and lead to negative impacts on the quality of life in the aging population. Most falls in older fallers result from unrecoverable limb collapse during falling momentum control in the single limb support (SLS) phase. To understand why older adults are more likely to fall than younger adults, we investigated age-related differences in knee extensor eccentric control, lower limb muscle activation patterns, and their relation to balance control. Ten older and ten younger healthy adults were compared during balance control while walking on a compliant surface. There was a positive correlation between knee extensor eccentric work in the perturbed leg and the swinging leg’s speed and margin of stability. In comparison to younger adults, older adults demonstrated (1) less eccentric work, reduced eccentric electromyography burst duration in the perturbed leg, (2) higher postural sway during SLS, and (3) impaired swinging leg balance control. The group-specific muscle synergy showed that older adults had a prominent ankle muscle activation, while younger adults exhibited a more prominent hip muscle activation. These findings provide insight into targeted balance rehabilitation directions to improve postural stability and reduce falls in older adults