Isokinetic Fatigue Protocol Research Articles

A Feasible and Reliable Muscle Fatigue Assessment Protocol for Individuals with Cerebral Palsy

To develop a reliable and feasible isokinetic fatigue protocol for the knee flexors and extensors in individuals with cerebral palsy (CP) who are ambulatory. Twelve subjects with CP, 10 to 23 years old, participated in the study. The protocol consisted of repeated maximum voluntary concentric knee flexion and extensions at 60 degrees /sec for a minimum of 35 repetitions. Fatigue Index (FI) and slope of the linear regression were computed. Reliability tests conducted a week later with five of the 12 subjects. Intraclass correlation coefficients were calculated for test-retest reliability. All subjects completed 35 repetitions, with only half reaching a 50% decline. All fatigue parameters were reliable for both knee flexors and extensors (slope: 0.94 and 0.97; slope/peak torque: 0.83 and 0.99; FI: 0.73 and 0.86, respectively). This isokinetic fatigue protocol is reliable and feasible for children and young adults with mild to moderate CP.

Fatigue Differences between Adults and Prepubertal Males

The purpose of the present study was to investigate the differences in neuromuscular activation of agonist and antagonist muscles between men and prepubertal boys during a maximal isokinetic fatigue test. Ten prepubertal boys (mean +/- SD age: 10.5 +/- 0.6 years) and fourteen adults (age: 24.3 +/- 2.5 years) executed 25 consecutive maximal isokinetic knee extensions at 60 deg . s (-1). Peak torque and the electromyogram (EMG) of the vastus lateralis, vastus medialis and biceps femoris muscles were recorded. During the fatigue protocol, the prepubertal boys were able to produce higher torque than the adults, when expressed as percent of their maximal value, indicating that adults were more fatigable. The agonist activity, especially for the vastus lateralis muscle, increased in both groups during the first 10 knee extensions, and then decreased more in adults. The antagonist activity of biceps femoris muscle in adults remained constant throughout the fatigue task, whereas the children showed, on average, an increased biceps femoris antagonistic activation, especially during the first 10 and last 5 knee extensions. These results suggest that adults are more fatigable than children during a maximal isokinetic fatigue protocol, probably due to an increased inhibition or reduced facilitation of their agonist drive.

Chronic Ankle Instability and Fatigue Create Proximal Joint Alterations during Performance of the Star Excursion Balance Test

The combined effects of chronic ankle instability (CAI) and lower extremity fatigue on measures of neuromuscular control have not been well established. The purpose of this study was to investigate the influence of CAI on the performance of a dynamic postural control task, the Star Excursion Balance Test (SEBT), after fatiguing activities. Thirty subjects with (n = 14) or without (n = 16) unilateral CAI completed anterior, medial, and posterior reaching directions of the SEBT performed before and after a lunging fatigue protocol and an open chain ankle isokinetic fatigue protocol. Pre-post fatigue change scores were calculated for sagittal plane kinematics of the stance leg and the normalized reach distances (%MAXD). Using a regression model, group and kinematic data were used to explain between subject differences in %MAXD. For each reaching direction, a separate analysis was completed for the two fatigue conditions. When reaching anteriorly after the lunge fatigue condition, CAI and the changes in knee and hip flexion predicted approximately 49 % of the variance in %MAXD (R2 = .487; p = .001). When reaching medially under lunge fatigue, CAI predicted approximately 20 % of the variance in %MAXD (R2 = .198; p = .014). Isolated ankle fatigue did not cause significantly different responses between groups. For two of the reaching directions, CAI status significantly influenced the variances in %MAXD under the influence of lunge fatigue. Functional fatigue protocols

Agonist and antagonist muscle activation during maximal and submaximal isokinetic fatigue tests of the knee extensors

The purpose of this study was to examine the differences in electromyographic activity of agonist and antagonist knee musculature between a maximal and a submaximal isokinetic fatigue protocol. Fourteen healthy males (age: 24.3 ± 2.5 years) performed 25 maximal (MIFP) and 60 submaximal (SIFP) isokinetic concentric efforts of the knee extensors at 60° s −1, across a 90° range of motion. The two protocols were performed a week apart. The EMG activity of vastus medialis (VM), vastus lateralis (VL) and biceps femoris (BF) were recorded using surface electrodes. The peak torque (PT) and average EMG (aEMG) were expressed as percentages of pre-fatigue maximal value. One-way analysis of variance indicated a significant ( p < 0.05) decline of PT during the maximal (45.7%) and submaximal (46.8%) protocols. During the maximal test, the VM and VL aEMG initially increased and then decreased. In contrast, VM and VL aEMG continuously increased during submaximal testing ( p < 0.05). The antagonist (BF) aEMG remained constant during maximal test but it increased significantly and then declined during the submaximal testing. The above results indicate that agonist and antagonist activity depends on the intensity of the selected isokinetic fatigue test.

Differences in recovery process between adult and prepubertal males after a maximal isokinetic fatigue task

The purpose of this study was to investigate the differences in recovery between adult and prepubertal males after a maximal isokinetic fatigue protocol. Ten adults and 14 prebupertal boys exerted 25 subsequent maximal isokinetic knee extensions at 60 ◦ /s. The electromyogram (EMG) of the vastus lateralis (VL), vastus medialis (VM) and biceps femoris (BF) was recorded. The obtained results showed that the Peak Torque (PT) decreased at a higher rate in adults compared to children. The recovery of PT, and the agonist muscle activity was faster in children in comparison to the men. No differences were observed in the recovery of the antagonist muscle between age groups. The findings indicated that the PT recovery is faster in children and this could be partially attributed to neural factors since in children the recovery of their agonist muscle activation was faster than adults.

The differential effects of fatigue on reflex response timing and amplitude in males and females

We examined the effects of fatigue on patellar tendon reflex responses in males and females. A spring-loaded reflex hammer elicited a standardized tendon tap with the knee positioned in an isokinetic dynamometer and flexed to 85°. We recorded vastus lateralis activity (SEMG) and knee extension force production at the distal tibia (force transducer). Reflex trials were performed before and after (immediate, 2, 4, and 6 min) an isokinetic fatigue protocol to 50% MVC (90°/s). For each event, pre-motor time (PMT), electromechanical delay (EMD), and total motor time (TMT) were obtained, as well as EMG amplitude (EMG amp), time to peak EMG (EMG tpk), peak force amplitude (F amp), time to peak force (F tpk), EMG:force ratio (E:F), and rate of force production (F rate=N/ms). TMT increased significantly in females following fatigue, while males showed no change. The increased TMT was due to an increased EMD with fatigue, while PMT was unaffected. EMG amp and F amp were somewhat diminished in females yet significantly augmented in males following fatigue, likely accounting for the differential changes in EMD noted. Results suggest males and females may respond differently to isokinetic fatigue, with males having a greater capacity to compensate for contraction force failure when responding to mechanical perturbations.

Effect of Plantar Flexor and Dorsiflexor Fatigue on Unilateral Postural Control

The purpose of this study was to determine the effect of plantar flexor and dorsiflexor fatigue on postural sway amplitude during unilateral, or one-legged, stance. It was hypothesized that plantar flexor and dorsiflexor fatigue would increase unilateral postural sway amplitude. Eight uninjured male subjects participated in pre- and postfatigue unilateral stability tests. Selected parameters describing medial-lateral (ML) and anterior-posterior (AP) postural sway were measured on a Chattecx Balance System before and after an isokinetic fatigue protocol. The fatigue protocol resulted in a significant increase in ML postural sway amplitude (p&lt; 0.05) and an increase in AP sway amplitude (p= 0.065). Previously, links have been established between increased postural sway amplitude and ankle joint injury. Thus, fatigue of the plantar flexors and dorsiflexors, which increased postural sway amplitude, may render the ankle joint susceptible to injury. Induced ankle muscle fatigue may represent a valid paradigm to study the causes of traumatic ankle joint injury.