The beneficial role of exercise in preventing doxorubicin-induced cardiotoxicity.

Doxorubicin is a highly effective chemotherapeutic agent widely used to treat a variety of cancers. However, the clinical application of doxorubicin is limited due to its adverse effects on several tissues. One of the most serious side effects of doxorubicin is cardiotoxicity, which results in life-threatening heart damage, leading to reduced cancer treatment success and survival rate. Doxorubicin-induced cardiotoxicity results from cellular toxicity, including increased oxidative stress, apoptosis, and activated proteolytic systems. Exercise training has emerged as a non-pharmacological intervention to prevent cardiotoxicity during and after chemotherapy. Exercise training stimulates numerous physiological adaptations in the heart that promote cardioprotective effects against doxorubicin-induced cardiotoxicity. Understanding the mechanisms responsible for exercise-induced cardioprotection is important to develop therapeutic approaches for cancer patients and survivors. In this report, we review the cardiotoxic effects of doxorubicin and discuss the current understanding of exercise-induced cardioprotection in hearts from doxorubicin-treated animals.

Four weeks of electrical stimulation improves glucose tolerance in a sedentary overweight or obese Hispanic population.

Introduction/purpose: Most US adults (54%) do not meet the minimum exercise recommendations by the American College of Sports Medicine. Neuromuscular electrical stimulation (NMES) is a novel alternate strategy to induce muscle contraction. However, the effectiveness of NMES to improve insulin sensitivity and energy expenditure is unclear. The purpose of this study was to investigate the effects of 4 weeks of NMES on glucose tolerance in a sedentary overweight or obese population. Methods: Participants (n = 10; age: 36.8 ± 3.8 years; BMI = 32 ± 1.3 kg/m2) were randomized into either control or NMES group. All participants received bilateral quadriceps stimulation (12 sessions; 30 min/session; three times/week at 50 Hz and 300 µs pulse width) altering pulse amplitude to either provide low-intensity sensory level (control; tingling sensation) or at high-intensity neuromuscular level (NMES; maximum tolerable levels with visible muscle contraction). Glucose tolerance was assessed by a 3-h oral glucose tolerance test (OGTT), and substrate utilization was measured by indirect calorimetry and body composition via dual X-ray absorptiometry at baseline and after 4 weeks of NMES intervention. Results: Control and NMES groups had comparable fasting blood glucose, glucose tolerance, substrate utilization, and muscle mass at baseline. Four weeks of NMES resulted in a significant improvement in glucose tolerance measured by OGTT, whereas no change was observed in the control group. There was no change in substrate utilization and muscle mass in both control and NMES groups. Conclusion: NMES is a novel and effective strategy to improve glucose tolerance in an at-risk overweight or obese sedentary population.

Neuromuscular responses at acute moderate and severe hypoxic exposure during fatiguing exercise of the biceps brachii.

PURPOSE: The present study examined acute normobaric hypoxic exposure on the number of repetitions to failure, electromyographic (EMG) repetition duration (Time), EMG root mean square (RMS) and EMG mean power frequency (MPF) during biceps brachii (BB) dynamic constant external resistance (DCER) exercise. METHODS: Thirteen subjects performed two sets of fatiguing DCER arm curl repetitions to failure at 70% of their one repetition maximum under normoxic (NH), moderate hypoxia FiO2 = 15% (MH) and severe hypoxia FiO2 = 13% (SH). Electromyography of the BB was analyzed for EMG Time, EMG RMS, and EMG MPF. Repetitions were selected as 25%, 50%, 75%, and 100% of total repetitions (%Fail) completed. Pulse oximetry (SpO2) was measured pre-and post-fatigue. RESULTS: There was no significant three-way (Condition x Set x %Fail) or two-way (Condition x Set) interaction for any variable. The number of repetitions to failure significantly decreased from (mean ± SEM) 18.2 ± 1.4 to 9.5 ± 1.0 with each Set. In addition, EMG Time increased (25% < 50%<75% < 100%), EMG RMS decreased (50% > 75%>100%), and EMG MPF decreased (75% > 100%) as a result of fatiguing exercise. SpO2 was lower during MH (Δ5.3%) and SH (Δ9.2%) compared to NH and as a result of fatiguing exercise increased only in MH (Δ2.1%) and SH (Δ5.7%). CONCLUSION: The changes in BB EMG variables indicated exercise caused myoelectric manifestations of fatigue, however, acute moderate or severe hypoxia had no additional influence on the rate of fatigue development or neuromuscular parameters.

Children With Autism Exhibit More Individualized Responses to Live Animation Biofeedback Than Do Typically Developing Children.

Children with autism have displayed imbalances in responding to feedback and feedforward learning information and they have shown difficulty imitating movements. Previous research has focused on motor learning and coordination problems for these children, but little is known about their motoric responses to visual live animation feedback. Thus, we compared motor output responses to live animation biofeedback training in both 15 children with autism and 15 age- and sex-matched typically developing children (age range: 8-17 years). We collected kinematic data via Inertial Measurement Unit devices while participants performed a series of body weight squats at a pre-test, during live animation biofeedback training, and at post-test. Dependent t-tests (α = 0.05), were used to test for statistical significance between pre- and post-test values within groups, and repeated measures analyses of variance (α = 0.05) were used to test for differences among the training blocks, within each group. The Model Statistic technique (α = 0.05) was used to test for pre- and post-test differences on a single-subject level for every participant. Grouped data revealed little to no significant findings in the children with autism, as these participants showed highly individualized responses. However, typically developing children, when grouped, exhibited significant differences in their left hip position (p = 0.03) and ascent velocity (p = 0.004). Single-subject analyses showed more individualistic live animation responses of children with autism than typically developing children on every variable of interest except descent velocity. Thus, to teach children with autism new movements in optimal fashion, it is particularly important to understand their individualistic motor learning characteristics.

Lesser magnitudes of lower extremity variability during terminal swing characterizes walking patterns in children with autism.

BACKGROUND: Anecdotally, children with Autism Spectrum Disorder have highly variable lower extremity walking patterns, yet, this has not been sufficiently quantified. As such, the purpose of this study was to examine walking pattern variability by way of lower extremity coordination and spatio-temporal characteristics in children with autism compared with individuals with typical development during over-ground walking. METHODS: Bilateral continuous relative phase variability was computed for the thigh-leg, leg-foot, and thigh-foot segment couples for 11 children with autism and 9 children with typical development at each gait sub-phase. Furthermore, left and right stride lengths and stride width were computed and compared. The Model Statistic was utilized to test for statistical differences in variability between each child with autism to an aggregate group with typical development. Effect sizes were computed to determine the meaningfulness between responses for children with autism and typical development. Coefficient of variation and effect sizes were computed for stride lengths and stride width. FINDINGS: Analysis revealed that children with autism exhibited differences in variability in each gait sub-phase. Notably, all but two children with autism exhibited lesser variability in all segment couples during terminal swing. Differences in stride lengths were relatively minimal, however, greater coefficient of variation magnitudes in stride width were observed in children with autism. INTERPRETATION: This finding reveals that children with autism may have limited or a preferred movement strategy when preparing the foot for ground contact. The findings from this study suggest variability may be an identifiable characteristic during movement in children with autism.

Sprint Training on a Treadmill vs. Overground Results in Modality-Specific Impact on Sprint Performance but Similar Positive Improvement in Body Composition in Young Adults.

Dorgo, S, Perales, JJ, Boyle, JB, Hausselle, J, and Montalvo, S. Sprint training on a treadmill vs. overground results in modality-specific impact on sprint performance but similar positive improvement in body composition in young adults. J Strength Cond Res 34(2): 463-472, 2020-The effects of different sprint training modalities on body composition are not yet known, and the effectiveness of using motorized treadmills for sprint training is yet to be assessed accurately. The following study investigated the effects of motorized treadmill and overground training on sprint performance and body composition. Sixty-four young adults (33 men and 31 women) completed 12 sprint training sessions over a 6-week period either on a treadmill (TM) or overground (TR), or followed their normal exercise routine (CONTROL). Fifty-yard sprint time, 20-yard maximal sprint speed split time, and maximal treadmill speed were used as sprint performance indicators. Body composition and sprint performance assessments were completed before and after the 6-week intervention. On completion of the 6-week training program, maximal treadmill speed significantly increased for all 3 groups, while split sprint time significantly decreased for the TR group. The CONTROL group's 50-yd sprint time and split sprint time significantly worsened after 6 weeks. Improvements in sprint time and speed were significantly greater for the TR and TM groups compared with the CONTROL group for 50-yd sprint time, 20-yard maximal sprint speed split time, and maximal treadmill sprint speed. The change in maximal treadmill sprint speed for the TM group was significantly greater than that of the TR group. TR and TM subjects also showed significant decrease in total body fat and increase in leg lean muscle mass. These findings indicate that although overground sprint training resulted in the greatest performance improvements within overground sprint tests, sprint training on a motorized treadmill may be a beneficial alternative modality to overground sprint training and may also positively impact subjects' body composition.

A Novel Approach to Enhancing Upper Extremity Coordination in Children with Autism Spectrum Disorder.

Recent studies examining children diagnosed with Autism Spectrum Disorder (ASD) have revealed kinematic markers highlighting deficits in the preparatory and online phases of upper extremity movements. In the following study, 12 children with high functioning ASD were first assessed (pre-test) on 15 trials of a reciprocal upper extremity Fitts Law target task by flexing and extending their right arm in the horizontal plane between two targets as fast and accurately as possible. Following the initial assessment, the children either continued with 30 additional trials of the target task (control) or were asked to track a sine wave template (experimental). All participants were then assessed on 15 trials of the target test (post-test). Results reveal that tracking the sine wave template during training not only produced faster movements compared to the control but also produced these movements in a more harmonic way.

Do accuracy requirements change bimanual and unimanual control processes similarly?

Unimanual (left and right limbs) and bimanual (in-phase) reciprocal aiming tasks were tested to determine if the control processes used to perform the unimanual aiming tasks were also present in bimanual aiming tasks. Participants were asked to move a cursor as quickly and accurately as possible between the two targets presented in a Lissajous feedback display. The size of the targets created indexes of difficulty (ID) of 3, 4, 5, and 6 and the position of the targets created bimanual and unimanual conditions. The results indicated that, as ID increased, the end-effectors' motion gradually switched from a cyclical to a more discrete motion for both unimanual and bimanual aiming tasks. However, the transition in control processes (i.e., the transition between cyclical and more discrete motions) tended to occur at a lower ID for the bimanual than the unimanual aiming tasks. Results also indicated that at ID6, bimanual aiming tasks were performed slower, more variable, and right limb dwelled at the targets longer than in the unimanual aiming task. No differences in performance were detected between the unimanual (left and right) and bimanual conditions at IDs 3-5. In terms of bimanual coordination, increasing the accuracy requirement resulted in decreased relative phase bias, but not more stable coupling between the two limbs.

Bimanual force control: cooperation and interference?

Three experiments were designed to determine the level of cooperation or interference observed from the forces generated in one limb on the forces exhibited by the contralateral limb when one or both limbs were producing a constant force (Experiment 1), one limb was producing a dynamic force while the other limb was producing a constant force (Experiment 2), and both limbs were producing dynamic force patterns (Experiment 3). The results for both Experiments 1 and 2 showed relatively strong positive time series cross correlations between the left and right limb forces indicating increases or decreases in the forces generated by one limb resulted in corresponding changes in the forces produced by the homologous muscles of the contralateral limb. Experiment 3 required participants to coordinate 1:1 and 1:2 rhythmical bimanual force production tasks when provided Lissajous feedback. The results indicated very effective performance of both bimanual coordination patterns. However, identifiable influences of right limb forces on the left limb force time series were observed in the 1:2 coordination pattern but not in the 1:1 pattern. The results of all three experiments support the notion that neural crosstalk is partially responsible for the stabilities and instabilities associated with bimanual coordination.

A novel approach to enhancing limb control in older adults.

Two recent experiments have demonstrated that young adult participants were able to make faster and more harmonic movements in a typical reciprocal Fitts task (ID = 6) following a practice session of sine wave tracking (Boyle et al. in Exp Brain Res 223:377-387, 2012; J Mot Behav 46:277-285, 2014). The purpose of the present experiment was to replicate these findings with a young adult population (age 18-25) and determine whether sine wave tracking also enhances goal-directed limb movements in an older adult population (age 65-90). To establish a performance baseline, all participants were first pretested on a typical ID = 6 Fitts task. Participants in each age group were then randomly assigned to one of the two training conditions where they practiced (45 trials) on a typical Fitts task (ID = 6) or they were asked to track a sine wave template (45 trials). Following practice, all participants were then posttested under the ID = 6 Fitts conditions. The results demonstrated that both young and older adult participants that practiced under the sine wave conditions enhanced their Fitts task performance compared to participants in their respective age groups who practiced under the Fitts conditions. These enhancements included faster movement times, smaller dwell times, and more harmonic movements, all without decreases in movement accuracy. These results replicate our previous findings with young adults and extend the finding to older adult participants. Interestingly, the performances of the older adults following sine wave practice were as fast and as accurate as the young adults following Fitts task practice.

Rhythmical bimanual force production: homologous and non-homologous muscles.

The experiment was designed to determine participants' ability to coordinate a bimanual multifrequency pattern of isometric forces using homologous or non-homologous muscles. Lissajous feedback was provided to reduce perceptual and attentional constraints. The primary purpose was to determine whether the activation of homologous and non-homologous muscles resulted in different patterns of distortions in the left limb forces that are related to the forces produced by the right limb. The task was to rhythmically produce a 1:2 pattern of isometric forces by exerting isometric forces on the left side force transducer with the left arm that was coordinated with the pattern of isometric forces produced on the right side force transducer with the right arm. The results indicated that participants were able to 'tune-in' a 1:2 coordination patterns using homologous (triceps muscles of the left and right limbs) and using non-homologous muscles (biceps left limb and triceps right limb) when provided Lissajous feedback. However, distinct but consistent and identifiable distortions in the left limb force traces were observed for both the homologous and non-homologous tasks. For the homologous task, the interference occurred in the left limb when the right limb was initiating and releasing force. For the non-homologous task, the interference in the left limb force occurred only when the right limb was releasing force. In both conditions, the interference appeared to continue from the point of force initiation and/or release to peak force velocity. The overall results are consistent with the notion that neural crosstalk manifests differently during the coordination of the limbs depending upon whether homologous or non-homologous muscles are activated.

The sine wave protocol: decrease movement time without increasing errors.

Practice tracking a sine wave template has been shown (J. B. Boyle, D. Kennedy, & C. H. Shea, 2012) to greatly enhance performance on a difficult Fitts task of the same amplitude. The purpose of the experiment was to replicate this finding and determine whether enhancements related to the sine wave practice are specific to the amplitude experienced during the sine wave practice. Following sine wave or Fitts task practice with amplitudes of 16° or 24°, participants were tested under the conditions they had practiced under (Test 1) and then all groups were tested under Fitts task conditions (Test 2; ID = 6, amplitude = 16°). Participants who practiced with the sine wave templates were able to move faster on Test 2 where a 16° amplitude Fitts task was used than participants that had practiced either the 16° or 24° amplitude Fitts tasks. The movements produced by the sine groups on Test 2 were not only faster than the movements of the Fitts groups on Test 2, but dwell time was lower with percent time to peak velocity and harmonicity higher for the Sine groups than for the Fitts groups. The decreased movement times for the sine groups on Test 2 were accomplished with hits or endpoint variability similar to that of the Fitts group.

Optimizing the control of high-ID movements: rethinking the power of the visual display.

A recent experiment by Boyle et al. (Exp Brain Res 223:377-387, 2012a) demonstrated that providing a sine-wave template for participants to follow enhances performance and transfer on difficult (ID = 6) Fitts tasks. Another experiment (Fernandez and Bootsma in Acta Psychol 129:217-227, 2008) demonstrated the effectiveness of applying a nonlinear transformation of the visual feedback provided to participants executing difficult aiming movements. The present experiment was designed to determine whether these two enhancements when used together would provide further enhancements to difficult aiming movements. Participants were randomly assigned to one of the three acquisition conditions. Participants in the Fitts and Fittslog condition were asked to flex/extend their arm in the horizontal plane at the elbow joint (wrist stabilized) in an attempt to move back and forth between two targets as quickly and accurately as possible. In the Sinelog condition, participants were asked to track a sine-wave pattern. The timing for Sinelog conditions was set to result in total times (movement time + dwell time) similar to that anticipated for the Fittslog condition. The feedback displays for Fittslog and Sinelog groups were subjected to a nonlinear transformation, but not for the Fitts group. Following 54 acquisition trials (17.5 s each) under their assigned condition, Test 1 was conducted under the same conditions as the participant experienced during the acquisition trials and Test 2 was conducted under Fitts conditions with the nonlinear transformation of the display data. Test 3 was conducted under typical Fitts conditions with no transformation of the display data. The results for Tests 1 and 2 indicated that total time and movement time for the Fittslog and Sinelog groups were reduced relative to the Fitts condition. In addition, dwell time was significantly lower, a larger proportion of movement time was spent in the acceleration portion of the movement, and normalized peak velocity was significantly lower for the participants in the Sinelog condition than for participants in the Fittslog condition. On Test 3, an untransformed Fitts condition was imposed; the Sinelog group outperformed the Fittslog condition on all variables except hits, endpoint variability, and peak velocity where the Fittslog and Sinelog groups performed similarly.

A guide to performing difficult bimanual coordination tasks: just follow the yellow brick road.

Both discrete and continuous bimanual coordination patterns are difficult to effectively perform when the two limbs are required to perform different movements patterns, move at different velocities and/or move different amplitudes unless some form of integrated feedback is provided. The purpose of the present experiment was to determine the degree to which a complex bimanual coordination pattern could be performed when integrated feedback and movement template are provided. The complex bimanual coordination pattern involved reciprocal movements of the two limbs under different difficulty requirements. As defined by Fitts' index of difficulty (ID), the left arm (ID = 3, A = 16°, W = 4°) task was of lower difficulty than the right arm task (ID = 5, A = 32°, W = 2°). Note that the left and right limb movements are also different in terms of movement time, movement velocity, accuracy requirements and amplitude as well as one movement was continuous and the other intermittent. Participants were provided 2 blocks of 9 trials in the bimanual condition (30 s/trial). Following the bimanual phase, participants performed two unimanual test trials-one with each limb. The results demonstrated that the performance for each limb in the bimanual condition was similar to the performance for the same limb and conditions in the unimanual control conditions. The similarity was indicated by the same movement speed, movement structure, endpoint variability and hit rates for the bimanual and unimanual conditions. The results support our hypothesis that people can overcome the intrinsic difficulties associated with performing complex bimanual coordination patterns when provided appropriate perceptual information feedback that allows them to detect and correct coordination errors.

Micro-movements of varying difficulties: wrist and arm movements.

An experiment was designed to determine the degree to which reducing movement amplitude (16°, 8°, to 4°) while keeping the relative accuracy requirements (IDs 1.5, 3, 4.5, and 6) and visual feedback display constant by increasing the display gain proportional to the decrease in amplitude (1×, 2×, 4×) influences reciprocal aiming movements of the wrist and arm. Research on smaller amplitude movements is limited and inconclusive, but these types of movement conditions are becoming increasingly more important as microsurgery and micro-mechanical applications increase. Participants were asked to flex/extend their limb/lever in the horizontal plane at the wrist (arm stabilized) or elbow joint (wrist stabilized) in an attempt to move back and forth between two targets as quickly and accurately as possible. The targets and current position of the limb were projected on the screen in front of the participant. Target width was manipulated with amplitude constant (16°, 8° or 4°). Results indicated that the linear relationship between MT and ID, typically observed for Fitts' tasks, was observed. There were moderate decreases in MT as amplitude was decreased but only for high ID movements. ID 6 movements at 4° amplitude, for example, were produced more quickly than at amplitude 16° without sacrificing end-point accuracy. The decrease in movement time was, however, related to increased dwell time and very low peak velocities.

Additional load decreases movement time in the wrist but not in arm movements at ID 6.

An experiment using reciprocal arm and wrist aiming movements with an amplitude of 16(o) and target width of .5° (ID = 6) was conducted to determine the impact of adding external loads. We predicted that wrist and arm performance may be differentially impacted by the added mass. Participants were asked to flex/extend their limb/lever in a horizontal plane at the wrist (arm stabilized) or elbow joint (wrist stabilized) in an attempt to move back and forth between the two targets as quickly and accurately as possible. External loads of 0, .568, or 1.136 kg were fixed at the distal end of the limb/lever. The targets and the current position of the limb were projected on the screen in front of the participant. The results indicated significant Group × Load interactions for movement time and percent time to peak velocity. Movement time decreased as load increased for the wrist but remained stable across loads for arm movements. Percent movement time utilized to accelerate the limb increased as load increased for wrist movements but only increased from 0 to .568 kg load for the arm movements. For both groups increased load had no significant effect on endpoint variability. The present findings suggest that the additional load allowed the control advantages of the wrist muscles to be exploited.

The role of auditory and visual models in the production of bimanual tapping patterns.

An experiment was designed to determine the effectiveness of auditory and visual models in the learning of a 2:3 bimanual tapping pattern. Participants were randomly assigned to an auditory model, visual model, auditory + visual model, or a control (visual metronome) group. The task for all groups was to tap a left side force transducer with the left hand and a right side force transducer with the right hand in attempt to produce the desired 2:3 bimanual coordination pattern. The auditory model consisted of a series of tones representing the goal pattern played prior to each practice trial. The visual model consisted of a visual display representing the goal tapping pattern. Visual pacing metronomes were provided to the control group. The right and left side metronomes flashed during the trial in a pattern representing the goal tapping pattern. Subjects in all groups performed 14 practice trials consisting of 15 s each devoted to tapping the goal pattern (total practice time = 3.5 min). A retention test without the aid of the models or metronomes was administered following the practice trials. The results for the model groups indicated extremely effective performance of the bimanual coordination patterns for the auditory, visual, and auditory + visual model conditions with not only the relative, but also the absolute characteristics of the models exhibited during retention testing. Retention performance for the visual metronome condition was less accurate and more variable than the three model conditions. In addition, the auditory + visual model condition resulted in retention performance that was more stable than the auditory model condition.

Wrist and arm movements of varying difficulties.

Although a great deal of experimental attention has been directed at understanding Fitts' law, only a limited number of experiments have attempted to determine if performance differs across effectors for a given movement difficulty. In three experiments reciprocal wrist and arm movements were compared at IDs of 1.5, 3, 4.5 and 6. When absolute movement requirements and visual display were constant, participants' movement times and response characteristics for the arm and wrist were remarkably similar (Experiment 1). However, when amplitude for wrist movements was reduced to 8° and the gain (4×) for the visual display increased participants' movement time, defined on the basis of kinematic markers (movement onset-movement termination), was increasingly shorter relative to arm movements as movement difficulty was increased (Experiment 2). Experiment 3 where the arm was tested at 32° and 8° with the 8° movements provided the same gain (4×) that was used for the 8° wrist movements in Experiment 2, no advantage was observed for the arm at the shorter amplitude. The results are interpreted in terms of the advantages afforded by the increased gain of the visual display, which permitted the wrist, but not the arm, to more effectively preplan and/or correct ongoing movements to achieve the required accuracy demands. It was also noted that while the wrist was more effective during the actual movement production this was accompanied by an offsetting increase in dwell time which presumably is utilized to dissipate the forces accrued during movement production and plan the subsequent movement segment.