An entire field of research was born when a paper entitled ‘On the education of muscular control and power’ first discussed a “psychical rather than a physical” bilateral adaptation to a unilateral training program. Although the true relevance of this paper would not be recognized for over a century, its novel findings, describing adaptations resulting from physical and skilled training, continue to influence scientific literature to this day. Most notably, Scripture coined the term ‘cross-education’ to describe the improvement in strength or functional performance of not only the trained limb but also in the untrained contralateral limb. Recently, unilateral training or ‘cross-education’ has been highlighted as a possible rehabilitation strategy during recovery from unilateral injuries. However, a number of limitations must be addressed within the scientific literature in order to properly apply unilateral resistance training as an effective rehabilitation strategy. Therefore, the primary goal of this dissertation was to address a number of fundamental issues related to optimizing unilateral resistance training. One such issue is knowledge on the time course of strength increase during unilateral resistance training. The primary purpose of Chapter 2 was to characterize the time-course of strength changes in both the trained and untrained limbs during unilateral handgrip training. Experiment 1 assessed the time-course with a ‘traditional’ training protocol (3x/week for 6 weeks: 18 total sessions) while Experiment 2 assessed a “compressed” protocol in which the number of sessions and contractions were matched but participants trained for eighteen consecutive days. An anticipated outcome was the determination of the minimum number of sessions required to induce contralateral strength gains in the upper limb. A secondary purpose of this study was to examine whether spinally-mediated adaptations in muscle afferent reflex pathways occur after unilateral handgrip training. Experiment 1 indicated six weeks of handgrip training significantly increased force output in both trained and untrained limbs. This strength increase was accompanied by changes in the maximal muscle activation in the trained limb only. Time course data indicated the trained limb was significantly stronger than baseline after the 3rd week of training (session 9) while the untrained limb was stronger after 5 weeks (15 sessions) of unilateral handgrip training. Interestingly, the rate at which strength increased in the untrained limb was similar to the trained side. These strength increases were also accompanied by significant changes in the current needed to produce H@50 in the trained, and Hmax in both the trained and untrained limb indicating alterations in spinal cord excitability. Experiment 2 showed a similar number of sessions was needed to induce significant strength gains in the untrained limb. This indicates training without rest days may be the most efficient protocol within a clinical population when the trained limb is not the focus of recovery. It remains necessary to determine if specific strategies can be employed to optimize unilateral resistance training interventions to increase strength gains. To date, no study has directly assessed the relative contribution of afferent pathways to cross-education. Cutaneous feedback from the skin provides perceptual information about joint position and movement. Unilateral training involves forceful contractions that activate cutaneous receptors in the skin, producing widespread and powerful effects between limbs. Providing “enhanced” cutaneous stimulation during unilateral contractions may alter excitability of interlimb reflex pathways, modifying the contralateral increase in strength. Therefore, the purpose of Chapter 3 was to determine the relative contribution of cutaneous afferent pathways as a mechanism of cross-education by directly assessing if unilateral cutaneous stimulation alters ipsilateral and contralateral strength gains. Participants were randomly assigned to either a voluntary contraction (TRAIN), cutaneous stimulation (STIM), or cutaneous stimulation during voluntary contraction (TRAIN+STIM) group. Each participant completed 6 sets of 8 reps 3x/week for 5 weeks. TRAIN included unilateral maximal voluntary isometric contractions (MVCs) of the wrist extensors. STIM training included cutaneous stimulation (2xRT for 3sec @ 50Hz) of the superficial radial (SR) nerve at the wrist only. TRAIN+STIM included MVCs of the wrist extensors with SR stimulation provided for the duration of the contraction. Two pre-training and 1 post-training session assessed the relative increase in force output during MVCs for wrist flexion, wrist extension and handgrip strength. Results indicated unilateral wrist extension training alone (TRAIN) increased force output in both trained and untrained wrist extensors. Providing ‘enhanced’ sensory feedback via electrical stimulation during training (TRAIN+STIM) led to similar increases in strength in the trained limb compared to TRAIN. However, the major finding revealed that ‘enhanced’ feedback in the TRAIN+STIM group completely blocked interlimb strength transfer to the untrained wrist extensors. It appears the large mismatched sensory volley which was provided may have interfered with the integration of the appropriate sensory cues to the untrained cortex and impaired the ability to induce “cross-education”. It may be possible to enhance effects of training by altering excitability via apparel such as compression garments. Currently, it is unknown whether tactile input to the skin induced via compression apparel may alter transmission of muscle afferent feedback within a limb. Thus, the purpose of Chapter 4 was to examine if sustained input to the skin via compression garment modulates sensory feedback transmission in the upper limb using the Hoffmann (H-) reflex as a probe. The purpose of these experiments was to: 1) explore the effects of compression gear on sensory feedback transmission in the upper limb during a static task, and 2) if the task (locomotor vs. reaching) or phase of a movement differentially modulated this transmission of sensory information. Furthermore, differences in performance of the discrete reaching task were assessed to provide data on whether a compression garment leads to alteration in motor task performance. Combined results from both parts of the study suggest that tactile input provided to the skin via compression garments modulates the excitability of afferent connections independent of descending input. The alteration in excitability occurs across multiple sensory pathways and across multiple movement tasks. Interestingly, there was a significant reduction in the number of errors made during the reaching task, which provides preliminary evidence of an improved performance while wearing a compression garment. Therefore, the compression sleeve appears to increase precision and sensitivity at the joint where it is applied. Overall, these results address many fundamental questions which have previously limited effective translation for rehabilitative interventions. These results provide preliminary guidelines for subsequent strength training interventions to prescribe the optimal ‘dose’ of unilateral strength training to maximize benefits while minimizing intervention burden. These studies also help refine a unifying model of unilateral strength training to include contributions from central motor output as well as afferent feedback. These studies highlight the importance of appropriate sensory feedback during maximal force production and the impact that sensory information from the skin can have on motor output in the nervous system. / Graduate / 0317 / 0719 / 0382

The purpose of this study was to examine the effects of a 4-week single-leg stance balance training program on balance error scoring system scores of the trained and untrained leg and to determine any differences between genders for balance performance and cross education. Participants (N = 35) between the ages of 18 - 31 from Utah State University were tested three times over a 4-week period and those in the training group trained for a total of 22 minutes over that same time. Results showed balance improved for the trained leg and the untrained leg as well (p = 0.23). Males and females also performed similarly (p = 0.95). These findings show balance can improve in both the trained leg and the untrained leg after only 22 minutes of training in 4 weeks and that men and women are nearly identical in balance performance and cross education improvements.

No description available.

PURPOSE: The purpose of this study was to examine the effects of short-term lower body unilateral resistance training on hormonal, muscle morphological, and performance measures in young men. METHODS: Seventeen healthy, untrained young men (Age: 22.8 ± 3.7 y; BMI: 26.5 ± 4.9 kg/m2) were randomly assigned to one of two groups (UT: 22.9 ± 4.6 y, 25.3 ± 4.2 kg/m2; CON: 24.0 ± 4.6 y, 27.7 ± 5.1 kg/m2). Resistance training consisted of 4 weeks of unilateral lower body and bilateral upper body exercises on 3 days per week. Each training session entailed unilateral countermovement jumps (3 × 8), unilateral leg press (LP), bilateral chest press (CP), unilateral leg extension (LE), and bilateral low row (LR). Strength exercises were performed for 3 sets of 8-10 repetitions; lower body exercises were performed with the dominant leg only. Muscle thickness (MT), pennation angle (PA), cross-sectional area (CSA), and echo-intensity (EI) of the vastus lateralis (VL) and rectus femoris (RF) muscles of both legs was assessed via ultrasound. Fascicle length (FL) was calculated as [MT / sin(PA)]. Maximal dynamic unilateral LP and LE strength was assessed during one-repetition maximum (1RM) testing; CP and LR 1RM strength was estimated as [repetition weight/(1.0278-0.0278)(reps)]. Maximal isometric knee extensor strength was isolaterally assessed via maximal voluntary contraction (MVC) testing. Mean and peak power output (Watts) was quantified during unilateral countermovement jumps via accelerometry. Fasting concentrations of total testosterone and growth hormone were obtained at baseline (PRE), immediately post (IP), 30-minutes post (30P), and 60-minutes post (60P) during both testing exercise sessions (Pre and Post). Following the 4-week intervention, all participants’ maximal dynamic and isometric strength, mean and peak power output, muscle morphology, and hormonal responses were reassessed. Performance, ultrasound, and area under the curve data were analyzed using ANCOVA to observe between-group comparisons while controlling for baseline (PRE) values. Endocrine data were analyzed using a two-way, mixedfactorial repeated-measures ANOVA. RESULTS: Participants in the UT group experienced significant strength improvements of the trained (28 to 150%) and untrained legs (12 to 160%). Training did not elicit significant improvements in maximal isometric strength or power output of the trained or untrained leg. The trained RF experienced significant increases in CSA and MT. The trained VL experienced a significant increase in CSA. Muscle size of the untrained leg was not significantly augmented. Training did not elicit changes in the acute hormonal response to exercise. CONCLUSIONS: Four weeks of unilateral lower body resistance training using the dominant leg appears sufficient to evoke strength gains of both the ipsilateral and contralateral legs. However, meaningful morphological changes were observed in the trained leg only. Differences in acute hormonal responses to resistance exercise did not appear to explain the observed differences. In addition, unilateral lower body resistance training did not appear to augment the acute endocrine response to an acute bout of resistance exercise. Current findings suggest that the cross-educational strength transfer during the early stage of training is attributable to factors other than changes in muscle morphology and circulating hormones.

Inledning: Stretching ökar rörelseförmågan över leden och har visats vara skadeförebyggande och en viktig del i rehabilitering. Rörligheten tros öka genom förlängning av kontraktil vävnad, ökad stretch-tolerans och anpassningar kopplade till aktivering av motoriska områden i hjärnan. Överföringseffekten innebär att den otränade (kontralaterala) extremiteten drar nytta av färdigheter som den tränade (unilaterala) extremiteten utvecklar något som kan ha stor nytta vid långvarig unilateral immobilisering. Syftet: Syftet med studien var att undersöka överföringseffekten från dynamisk- respektive statisk unilateral rörlighetsträning av hamstringsmusklatur till kontralateral sida efter två veckors intervention, samt jämföra effekterna däremellan. Metod: Fyra deltagare inkluderades och fördelades slumpmässigt mellan de två interventionerna. En grupp, deltagare 2 och 3, utförde unilateraldynamisk rörlighetsträning och den andra gruppen, deltagare 1 och 4, utförde unilateralstatisk rörlighetsträning. Rörligheten i hamstringsmuskulatur mättes med passive straight legraise (PSLR) och aktiv knäextension (AKE) innan och efter två veckors intervention. Resultat: Deltagare 1 och 2 visade en överföringseffekt på 6,4-11,3% vid mätning av AKE. Deltagare 2 visade en överföringseffekt på 6,3% vid mätning av PSLR. Deltagare 3 visade en minskning med 8% på kontralaterala benet vid mätning av PSLR. För övriga utfall visade deltagarna en förändring av rörligheten på ±3 grader. Diskussion: Överföringseffekt observerades vid hälften av utfallen och till största del vid mätning av AKE, utan skillnad mellan statisk och dynamisk rörlighetsträning. Tänkbar mekanism är en kombination av ökad stretch-tolerans och neurala adaptioner mellan hjärnbark, muskel och muskelspole. Konklusion: En viss överföringseffekt efter rörlighetsträning kan ej uteslutas men studier med fler deltagare behövs för att bekräfta resultatet av denna pilotstudie.