Unilateral, resistance training, cross education, endocrine, morphology, echo intensity


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.


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Graduation Date





Fragala, Maren


Master of Science (M.S.)


College of Education and Human Performance


Child, Family, and Community Sciences

Degree Program

Sport & Exercise Science; Applied Exercise Physiology Track








Release Date

August 2015

Length of Campus-only Access


Access Status

Masters Thesis (Open Access)


Dissertations, Academic -- Education and Human Performance; Education and Human Performance -- Dissertations, Academic