Effects of unstable load and unstable surface ontrunk muscles activation and postural control in healthy subjects.

Exercise with an unstable load is considered a new training method to activate the core muscles. Research has shown consistency regarding an unstable surface but has not provided comprehensive findings about the effect of an unstable load. The study aimed to examine the impact of an unstable load and unstable surfaces on core muscle activation and postural control during lifting. Thirty-eight participants lifted a load equivalent to 10 % of their body weight under three conditions: a stable load on an unstable surface, a stable load on a stable surface, and an unstable load on a stable surface. The center of pressure (COP) displacement and electromyography activity of abdominal and back extensor muscles were measured during lifting. The results indicated that lifting on an unstable surface activated the lumbar erector spinae and multifidus muscles more than in a stable condition (P<0.05). However, there was no significant difference in the level of thoracic erector spinae muscle activity between the unstable load and unstable surface conditions. The stable condition increased activity in the internal oblique muscle (1.37 times) compared to the unstable conditions. The analysis of postural control revealed that lifting the load on an unstable surface significantly decreased COP displacement in the anteroposterior direction (P<0.05), while holding the load on the unstable surface significantly increased COP displacement in the anteroposterior direction compared to the other conditions. These findings could be valuable for future rehabilitation research, learning appropriate lifting techniques, and setting specific training goals in sports.

Effect of non-elastic taping on vertical stiffness of healthy athletes during a basketball jump shot.

BACKGROUND: Basketball is a high-risk team sport for lower extremity injuries, with ankle sprains being the most common injury. Non-elastic tape is widely used in injury prevention and quick return to play after ankle sprains, but its impact on stiffness, particularly global stiffness, has not been thoroughly investigated. OBJECTIVES: The aim of this study was to investigate the effects of non-elastic ankle taping on vertical stiffness, among basketball players during the jump shot tasks; and to assess the reliability of accelerometers to evaluate vertical stiffness. DESIGN: Single group, repeated measures study. PARTICIPANTS: Thirty healthy semi-professional basketball players (15 males and 15 females) participated in the study. INTERVENTIONS: Vertical stiffness was compared among three conditions: 1) without taping, 2) while the non-elastic tape was applied to their ankles, and 3) after running while taped. Vertical stiffness was calculated from acceleration data using a mass-spring model. RESULTS: The result of a one-way repeated measures ANOVA showed that vertical stiffness was not significantly different between the three conditions (P = 0.162). Within-day and between-day reliability for average measurements were found to be high or very high. CONCLUSION: The findings showed that the vertical stiffness is unaffected by non-elastic taping. Therefore, while non-elastic tape can limit ankle range of motion, it may not have an impact on vertical stiffness, a global parameter which reflects the musculoskeletal performance. On the other hand, the high reliability of the stiffness variable supports the use of an accelerometer as a small portable instrument for outdoor sports measurements.

Fatigue effects on the viscoelastic behavior of men and women in a landing task: a Mass-Spring-Damper modeling approach.

The aim of this study was to compare the fatigue effect on the viscoelastic behavior of the musculoskeletal system between the two sexes in a landing task. Stiffness and shock absorption capacity were studied from ground reaction force data using a mass-spring-damper model. A parametric simulation was also performed to demonstrate the effect of different values of model parameters on the vertical ground reaction force. Following fatigue, the shock absorption capacity reduced in men. According to the parametric simulation, this reduction can result in lower rate of force development which may make men less susceptible to impact injuries than women.

Effect of Gastrocnemius Kinesio Taping on Countermovement Jump Performance and Vertical Stiffness Following Muscle Fatigue.

CONTEXT: Kinesio tape (KT) is a widely used intervention in the fields of sports and rehabilitation. However, its effects on lower-extremity behavior during functional activities are not entirely known. OBJECTIVE: To test the hypothesis that application of KT can change performance and vertical stiffness (VS) during the countermovement jump (CMJ) before and after a fatigue protocol. DESIGN: A predesign and postdesign to study the effect of KT in 2 situations, prefatigue and postfatigue. In each fatiguing condition, there were 2 conditions with and without KT application on the gastrocnemius muscle. SETTING: Biomechanics laboratory. PARTICIPANTS: Fifty healthy, nonathlete participants (26 females and 24 males). INTERVENTIONS: KT application on the gastrocnemius muscle and a fatigue protocol to induce fatigue in plantar flexor muscles. MAIN OUTCOME MEASURES: Various jumping parameters, including jump height, maximum force, maximum power, rate of force development, eccentric lower-limb stiffness, and VS, were calculated using the vertical ground reaction force data. Eccentric lower-limb stiffness and VS were calculated using a mass-spring model. The studied variables can present lower-extremity elastic behavior and performance during CMJ. RESULTS: The results of a 2-way repeated-measures analysis of variance showed no significant effect for KT application. Fatigue resulted in lower values of jump height, maximum power, and VS. Moreover, male subjects showed greater values of jump height, maximum force, and maximum power than did females. CONCLUSIONS: The main finding of this study was that gastrocnemius KT has no effect on performance or elastic behavior of the lower-extremity during CMJ. Moreover, KT cannot reduce the adverse effect of fatigue in a functional activity such as CMJ. It seems that gastrocnemius KT is not effective for demanding activities.

Fatigue Effect on Linear Center of Pressure Measures during Gait in People with Flat Feet.

BACKGROUND: Flat foot, as one of the common foot deformities can affect gait biomechanics and risk of lower extremity injury. Fatigue, as a high load task, can also change biomechanical parameters of locomotion. Studying normal and flat footed individuals under high load tasks such as fatigue can elucidate their differences more easily. OBJECTIVES: In this study, center of pressure (CoP) changes were studied between individuals with flat and normal feet after fatigue. CoP is one of the important gait measures which can show various biomechanical behaviors of different foot shapes. METHODS: Seventeen subjects with normal feet and 17 with flat feet walked across two force plates before and after a functional fatigue protocol. Standard deviation of CoP in mediolateral direction (SD of CoPx) and in anteroposterior direction (SD of CoPy), overall mean velocity of CoP and length of CoP construction line of both groups were analyzed. The values of SD of CoPy and length of CoP construction line were normalized to individual foot lengths prior to statistical analyses. RESULTS: There were no significant between-subject effects for all CoP measures. The only significant finding was the within-subject effect for the SD of CoPy (P = 0.008) with a large effect size (partial eta squared = 0.21). Fatigue resulted in lower SD of CoPy in both groups. CONCLUSIONS: Lower SD of CoPy indicates less fluctuation of CoPy and a probable less center of mass movement which could reduce the risk of injury. Furthermore, the similar fatigue response in both groups of individuals with normal and flat feet indicates a similar biomechanical behavior despite their different foot arch height.

Effect of functional fatigue on vertical ground-reaction force in individuals with flat feet.

CONTEXT: Flat foot is one of the lower extremity deformities that might change kinetic variables of gait. Fatigue is one of the factors that can alter the vertical ground-reaction force (GRF). The effect of a fatiguing condition on vertical GRF has not been documented in individuals with flat feet. OBJECTIVE: To examine the fatigue effect on vertical GRF in individuals with flat feet compared with a normal group during barefoot walking. DESIGN: Repeated-measure ANOVA for the effects of fatigue on individuals with flat feet and normal feet. SETTING: Biomechanics laboratory. PARTICIPANTS: 17 subjects with flat feet and 17 normal subjects (recruited according to their arch-height ratio). MAIN OUTCOME MEASURES: Three vertical GRF measures (F1, the first peak force; F2, minimum force; and F3, the second peak force) were extracted before and after a functional fatigue protocol. RESULTS: No significant interaction between fatigue and group was observed for the 3 vertical GRF measures. For F2, fatigue and group effects were significant (P = .001 and P = .02, respectively). Furthermore, F2 was higher in the flat-feet group than in the normal group; F2 also increased after fatigue. For F3, only a significant fatigue effect was observed (P = .004). F3 decreased after fatigue in both groups. CONCLUSIONS: In the flat-feet group, a decrease in the variation of vertical GRF might be due to more flexible foot joints. After fatigue, muscles might lose their ability to control the foot joints and cause higher F2 in the flat-feet group.