Unilateral Isometric Strength Research Articles

Reactive Strength as a Metric for Informing Return-to-Sport Decisions: A Case-Control Study.

Current return-to-sport decisions are primarily based on elapsed time since surgery or injury and strength measures. Given data that show rates of successful return to competitive sport at around 55%, there is strong rationale for adopting tools that will better inform return to sport decisions. The authors' objective was to assess reactive strength as a metric for informing return-to-sport decisions. Case-control design. Fifteen elite athletes from national sports teams (23 [6.0]y) in the final phase of their return-to-sport protocol following a unilateral knee injury and 16 age-matched control athletes (22 [4.6]y) performed a unilateral isometric strength test and 24-cm drop jump test. Pairwise comparisons were used to determine differences between legs within groups and differences in interleg asymmetry between groups. Strength measures did not distinguish the control from the rehabilitation group; however, clear differences in the degree of asymmetry were apparent between the control and rehabilitation groups for contact time (Cohen d = 0.56; -0.14 to 1.27; 8.2%; P = .113), flight time (d = 1.10; 0.44 to 1.76; 16.0%; P = .002), and reactive strength index (d = 1.27; 0.50 to 2.04; 22.4%; P = .002). Reactive strength data provide insight into functional deficits that persist into the final phase of a return-to-sport protocol. The authors' findings support the use of dynamic assessment tools to inform return-to-sport decisions to limit potential for reinjury.

Effectiveness of an Unexpected Disturbance Program in the Early Stage of Rehabilitation in Athletes With Unilateral Knee Ligament Injury.

Sensorimotor, proprioceptive, and neuromuscular programs are critical for the successful rehabilitation of injured athletes, and these decrease reinjury rates. To investigate the effects of an unexpected disturbance program (UDP) on balance and unilateral strength metrics in athletes with unilateral knee ligament injury. A 3-week parallel-group experimental design consisting of 9 rehabilitation sessions. National Sports Institute. Twenty-one national-level athletes (age 21.4 [4.4]y, body mass 63.9 [10.8]kg, height 169.0 [10.2]cm) who had sustained a unilateral knee ligament injury. An UDP program designed to evoke rapid sensorimotor responses was compared with traditional training and a nonexercise control group. Unilateral total, anteroposterior, and mediolateral sway with eyes open and closed and unilateral isometric strength. Traditional exercises tended to outperform the UDP when unilateral balance testing was performed with eyes open; however, balance improvement following UDP tended to be greater in the eyes-closed condition. Significant strength gains in both the injured and uninjured legs were only observed following the UDP. This increase in unilateral isometric strength was 23.4 and 35.1 kg greater than the strength improvements seen in the traditional rehabilitation and control groups (P < .05). UDP could improve neural aspects of rehabilitation to improve rehabilitation outcomes by improving strength, sensorimotor function, and proprioception. Given the complementary adaptations, an UDP could provide an effective adjunct to traditional rehabilitation protocols and improve return-to-play outcomes.

Training intensity-dependent increases in corticospinal but not intracortical excitability after acute strength training.

The purpose of this study was to determine whether the increases in corticospinal excitability (CSE) observed after one session of unilateral isometric strength training (ST) are related to changes in intracortical excitability measured by magnetic brain stimulation (TMS) in the trained and the contralateral untrained biceps brachii (BB) and whether such changes scale with training intensity. On three separate days, 15 healthy young men performed one ST session of 12 sets of eight isometric contractions of the right elbow flexors at 0% (control session), 25%, or 75% of the maximal voluntary contraction (MVC) in a random order. Before and after each session separated at least by 1week, motor evoked potential (MEP) amplitude, short-interval intracortical inhibition (SICI), contralateral silent period (SP), and intracortical facilitation (ICF) generated by TMS were measured in the trained and the untrained BBs. Compared with baseline, MEPs recorded from the trained BB increased by ~47% after training at 75% of MVC (P<.05) but not after training at 0% (~4%) or 25% MVC (~5%, both P>.05). MEPs in the untrained BB and SICI, SP, and ICF in either BB did not change. Therefore, acute high-intensity but not low-intensity unilateral isometric ST increases CSE in the trained BB without modifications in intracortical inhibition or facilitation. Thus, increases in corticospinal neurons or α-α-motoneuron excitability could underlie the increases in CSE. Regardless of contraction intensity, acute isometric ST did not modify the excitability of the ipsilateral primary motor cortex measured by TMS.

Changes in motor unit discharge patterns following strength training.

Changes in motor unit discharge patterns following strength training.

The time course of cross-education during short-term isometric strength training.

This study examined the time course of contralateral adaptations in maximal isometric strength (MVC), rate of force development (RFD), and rate of electromyographic (EMG) rise (RER) during 4weeks of unilateral isometric strength training with the non-dominant elbow flexors. Twenty participants were allocated to strength training (n = 10, three female, two left hand dominant) or control (n = 10, three female, two left hand dominant) groups. Both groups completed testing at baseline and following each week of training to evaluate MVC strength, EMG amplitude, RFD and RER at early (RFD50, RER50) and late (RFD200, RER200) contraction phases for the dominant 'untrained' elbow flexors. The training group completed 11 unilateral isometric training sessions across 4weeks. The contralateral improvements for MVC strength (P < 0.01) and RFD200 (P = 0.017) were evidenced after 2weeks, whereas RFD50 (P < 0.01) and RER50 (P = 0.02) showed significant improvements after 3weeks. Each of the dependent variables was significantly (P < 0.05) greater than baseline values at the end of the training intervention for the trained arm. No changes in any of the variables were observed for the control group (P > 0.10). Unilateral isometric strength training for 2-3weeks can produce substantial increases in isometric muscle strength and RFD for both the trained and untrained arms. These data have implications for rehabilitative exercise design and prescription.

Unilateral Isometric Squat: Test Reliability, Interlimb Asymmetries, and Relationships With Limb Dominance

Bishop, C, Read, P, Lake, J, Loturco, I, Dawes, J, Madruga, M, Romero-Rodrigues, D, Chavda, S, and Turner, A. Unilateral isometric squat: Test reliability, interlimb asymmetries, and relationships with limb dominance. J Strength Cond Res 35(2S): S144-S151, 2021-The aim of this study was to determine test reliability, establish interlimb asymmetries and their associations with force production capability on the dominant (D) and nondominant (ND) limbs during the unilateral isometric squat test. Twenty-eight recreational sport athletes attended a single-test session after familiarization and performed 3 trials on each limb with 140° of hip and knee flexion, to assess peak force (PF), rate of force development (RFD), and impulse at different time intervals. Reliability, interlimb asymmetries, and Pearson's r correlations were computed thereafter. Test reliability was metric-dependent with only PF showing good levels of reliability on both limbs (coefficient of variation = 5.44-5.70; intraclass correlation coefficient = 0.93-0.94). Interlimb asymmetries ranged from 8.36 to 25.46%, with a tendency for RFD and impulse asymmetries to reduce as time intervals increased. Three significant negative relationships of a possible 49 (r = -0.43 to -0.47; p < 0.05) were found between asymmetries and performance on the D limb. However, 31 significant negative correlations (r = -0.42 to -0.71; p < 0.05) were found between asymmetries and performance on the ND limb. These findings demonstrate that practitioners may only be able to use PF as a reliable test metric during a unilateral isometric strength test. Furthermore, the negative association between asymmetries and strength performance on the ND limb may indicate that the reduction of imbalances through targeted training interventions may be warranted.

Neuromuscular Adaptations to Unilateral vs. Bilateral Strength Training in Women.

Botton, CE, Radaelli, R, Wilhelm, EN, Rech, A, Brown, LE, and Pinto, RS. Neuromuscular adaptations to unilateral vs. bilateral strength training in women. J Strength Cond Res 30(7): 1924-1932, 2016-Considering the bilateral deficit, the sum of forces produced by each limb in a unilateral condition is generally greater than that produced by them in a bilateral condition. Therefore, it can be speculated that performing unilateral strength exercises may allow greater training workloads and subsequently greater neuromuscular adaptations when compared with bilateral training. Hence, the purpose of this study was to compare neuromuscular adaptations with unilateral vs. bilateral training in the knee extensor muscles. Forty-three recreationally active young women were allocated to a control, unilateral (UG) or bilateral (BG) training group, which performed 2 times strength training sessions a week for 12 weeks. Knee extension one repetition maximum (1RM), maximal isometric strength, muscle electrical activity, and muscle thickness were obtained before and after the study period. Muscle strength was measured in unilateral (right + left) and bilateral tests. Both UG and BG increased similarly their unilateral 1RM (33.3 ± 14.3% vs. 24.6 ± 11.9%, respectively), bilateral 1RM (20.3 ± 6.8% vs. 28.5 ± 12.3%, respectively), and isometric strength (14.7 ± 11.3% vs. 13.1 ± 12.5%, respectively). The UG demonstrated greater unilateral isometric strength increase than the BG (21.4 ± 10.5% vs. 10.3 ± 11.1%, respectively) and only the UG increased muscle electrical activity. Muscle thickness increased similarly for both training groups. Neither group exhibited pretesting 1RM bilateral deficit values, but at post-testing, UG showed a significant bilateral deficit (-6.5 ± 7.8%) whereas BG showed a significant bilateral facilitation (5.9 ± 9.0%). Thus, performing unilateral or bilateral exercises was not a decisive factor for improving morphological adaptations and bilateral muscle strength in untrained women. Unilateral training, however, potentiate unilateral specific strength gains.