Comparison of Cross-Education and Global Training Effects in Adults and Youth After Unilateral Strength Training.

ABSTRACT: Chaouachi, A, Ben Othman, A, Chaouachi, M, Hechmi, A, Farthing, JP, Granacher, U, and Behm, DG. Comparison of cross-education and global training effects in adults and youth after unilateral strength training. J Strength Cond Res 36(8): 2121-2131, 2022-Youth strength training research examining contralateral, homologous (cross-education), and heterologous (global training) effects after unilateral training have provided mixed results and the relationship to adults has not been compared. The objective was to compare adult and youth cross-education and global training effects on dominant and nondominant limb testing. Initially, 15 men and 15 prepubertal boys volunteered for each unilateral chest press (CP), handgrip training, and control groups ( n = 89). Individuals trained their dominant limb 3 times per week for 8 weeks and had their dominant and nondominant limbs tested for CP and leg press 1 repetition maximum (1RM), handgrip, knee extension and flexion, and elbow extension and flexion maximum voluntary isometric contractions (MVICs). Adult CP training gains were significantly greater than youth with lower-body testing ( p = 0.002-0.06), whereas youth CP training gains exceeded adults with upper-body tests ( p = 0.03-0.07). Training specificity was evident with greater CP 1RM increases with CP vs. handgrip training for both youth ( p < 0.0001) and adults ( p < 0.0001). Handgrip training elicited greater gains in handgrip MVICs compared with other strength tests ( p < 0.0001). In conclusion, only contralateral CP 1RM showed a training advantage for unilateral CP over unilateral handgrip training. Adults showed greater gains with lower-body testing, whereas youth showed greater gains with upper-body testing.

Unilateral Elbow Flexion and Leg Press Training Induce Cross-Education But Not Global Training Gains in Children.

PURPOSE: Whereas cross-education has been extensively investigated with adults, there are far fewer youth investigations. Two studies suggested that children had greater global responses to unilateral knee extensor fatigue and training, respectively, than adults. The objective of this study was to compare global training responses and cross-education effects after unilateral elbow flexion (EFlex) and leg press (LP) training. METHODS: Forty-three prepubertal youths (aged 10-13 y) were randomly allocated into dominant LP (n = 15), EFlex (n = 15) training groups, or a control (n = 13). Experimental groups trained 3 times per week for 8 weeks and were tested pretraining and posttraining for ipsilateral and contralateral 1-repetition maximum LP; knee extensor, knee flexors, elbow flexors; and handgrip maximum voluntary isometric contractions (MVIC), and countermovement jump. RESULTS: In comparison to no significant changes with the control group, dominant elbow flexors training demonstrated significant ( P < .001) improvements only with ipsilateral and contralateral upper body testing (EFlex MVIC [15.9-21.5%], EFlex 1-repetition maximum [22.9-50.8%], handgrip MVIC [5.5-13.8%]). Dominant LP training similarly exhibited only significant ( P < .001) improvements for ipsilateral and contralateral lower body testing (LP 1-repetition maximum [59.6-81.8%], knee extensor MVIC [12.4-18.3%], knee flexor MVIC [7.9-22.3%], and countermovement jump [11.1-18.1%]). CONCLUSIONS: The ipsilateral and contralateral training adaptations in youth were specific to upper or lower body training, respectively.

Dominant and nondominant leg press training induce similar contralateral and ipsilateral limb training adaptations with children.

Cross-education has been extensively investigated with adults. Adult studies report asymmetrical cross-education adaptations predominately after dominant limb training. The objective of the study was to examine unilateral leg press (LP) training of the dominant or nondominant leg on contralateral and ipsilateral strength and balance measures. Forty-two youth (10-13 years) were placed (random allocation) into a dominant (n = 15) or nondominant (n = 14) leg press training group or nontraining control (n = 13). Experimental groups trained 3 times per week for 8 weeks and were tested pre-/post-training for ipsilateral and contralateral 1-repetition maximum (RM) horizontal LP, maximum voluntary isometric contraction (MVIC) of knee extensors (KE) and flexors (KF), countermovement jump (CMJ), triple hop test (THT), MVIC strength of elbow flexors (EF) and handgrip, as well as the stork and Y balance tests. Both dominant and nondominant LP training significantly (p < 0.05) increased both ipsilateral and contralateral lower body strength (LP 1RM (dominant: 59.6%-81.8%; nondominant: 59.5%-96.3%), KE MVIC (dominant: 12.4%-18.3%; nondominant: 8.6%-18.6%), KF MVIC (dominant: 7.9%-22.3%; nondominant: nonsignificant-3.8%), and power (CMJ: dominant: 11.1%-18.1%; nondominant: 7.7%-16.6%)). The exception was that nondominant LP training demonstrated a nonsignificant change with the contralateral KF MVIC. Other significant improvements were with nondominant LP training on ipsilateral EF 1RM (6.2%) and THT (9.6%). There were no significant changes with EF and handgrip MVIC. The contralateral leg stork balance test was impaired following dominant LP training. KF MVIC exhibited the only significant relative post-training to pretraining (post-test/pre-test) ratio differences between dominant versus nondominant LP cross-education training effects. In conclusion, children exhibit symmetrical cross-education or global training adaptations with unilateral training of dominant or nondominant upper leg.

Global Training Effects of Trained and Untrained Muscles With Youth Can be Maintained During 4 Weeks of Detraining.

Chaouachi, A, Ben Othman, A, Makhlouf, I, Young, JD, Granacher, U, and Behm, DG. Global training effects of trained and untrained muscles with youth can be maintained during 4 weeks of detraining. J Strength Cond Res 33(10): 2788-2800, 2019-Global (whole-body) effects of resistance training (i.e., cross-education) may be pervasive with children. Detraining induces less substantial deficits with children than adults. It was the objective of this study to investigate the global responses to 4 weeks of detraining after 8 weeks of unilateral leg press (LP) training in 10-13-year-old, pre-peak-height-velocity stage boys. Subjects were randomly separated into 2 unilateral resistance training groups (high load/low repetitions [HL-LR] and low load/high repetitions [LL-HR], and control group). Assessments at pre-training, post-training, and detraining included dominant and nondominant limbs, unilateral, 1 repetition maximum (1RM) and 60% 1RM LP, knee extension, knee flexion, elbow flexion, and handgrip maximal voluntary isometric contraction (MVIC), and countermovement jump (CMJ). All measures significantly increased from pre-test to detraining for both training programs, except for elbow flexion MVIC with increases only with HL-LR. All measures except CMJ and handgrip MVIC significantly decreased from post-test to detraining, except for elbow flexion MVIC with decreases only with HL-LR. The dominant trained limb experienced significantly greater LP improvements (pre- to detraining) and decrements (post- to detraining) with LP 1RM and 60% 1RM LP. In conclusion, youth HL-LR and LL-HR global training effects of trained and untrained limbs demonstrate similar benefits (pre- to detraining) and decrements (post- to detraining) with detraining. The findings emphasize that training any muscle group in a child can have positive global implications for improved strength and power that can persist over baseline measures for at least a month.

Combination of Agility and Plyometric Training Provides Similar Training Benefits as Combined Balance and Plyometric Training in Young Soccer Players.

Introduction: Studies that combined balance and resistance training induced larger performance improvements compared with single mode training. Agility exercises contain more dynamic and sport-specific movements compared with balance training. Thus, the purpose of this study was to contrast the effects of combined balance and plyometric training with combined agility and plyometric training and an active control on physical fitness in youth. Methods: Fifty-seven male soccer players aged 10-12 years participated in an 8-week training program (2 × week). They were randomly assigned to a balance-plyometric (BPT: n = 21), agility-plyometric (APT: n = 20) or control group (n = 16). Measures included proxies of muscle power [countermovement jump (CMJ), triple-hop-test (THT)], muscle strength [reactive strength index (RSI), maximum voluntary isometric contraction (MVIC) of handgrip, back extensors, knee extensors], agility [4-m × 9-m shuttle run, Illinois change of direction test (ICODT) with and without the ball], balance (Standing Stork, Y-Balance), and speed (10-30 m sprints). Results: Significant time × group interactions were found for CMJ, hand grip MVIC force, ICODT without a ball, agility (4 m × 9 m), standing stork balance, Y-balance, 10 and 30-m sprint. The APT pre- to post-test measures displayed large ES improvements for hand grip MVIC force, ICODT without a ball, agility test, CMJ, standing stork balance test, Y-balance test but only moderate ES improvements with the 10 and 30 m sprints. The BPT group showed small (30 m sprint), moderate (hand grip MVIC, ICODTwithout a ball) and large ES [agility (4 m × 9 m) test, CMJ, standing stork balance test, Y-balance] improvements, respectively. Conclusion: In conclusion, both training groups provided significant improvements in all measures. It is recommended that youth incorporate balance exercises into their training and progress to agility with their strength and power training.

Evidence of homologous and heterologous effects after unilateral leg training in youth.

The positive effects of unilateral training on contralateral muscles (cross education) has been demonstrated with adults for over a century. There is limited evidence for cross education of heterologous muscles. Cross education has not been demonstrated with children. It was the objective of this study to investigate cross-education training in children examining ipsilateral and contralateral homologous and heterologous muscles. Forty-eight male children (aged 10-13 years) were assessed for unilateral, ipsilateral and contralateral lower limb strength, power and endurance (1-repetition maximum (RM) leg press, knee extensors (KE) and flexors (KF) maximum voluntary isometric contractions (MVIC), countermovement jump, muscle endurance test (leg press repetitions with 60% 1RM)), and upper body unilateral MVIC elbow flexors (EF) and handgrip strength. An 8-week training program involved 2 unilateral leg press resistance-training groups (high load/low repetitions: 4-8 sets of 5RM, and low load/high repetitions: 1-2 sets of 20RM) and control (untrained) group. All muscles exhibited improvements of 6.1% to 89.1%. The trained limb exhibited greater adaptations than the untrained limb for leg press 1RM (40.3% vs. 25.2%; p = 0.005), and 60% 1RM leg press (104.1% vs. 73.4%; p = 0.0001). The high load/low repetition training induced (p < 0.0001) greater improvements than low load/high repetition with KE, KF, EF MVIC and leg press 1RM. This is the first study to demonstrate cross-education effects with children and that the effects of unilateral training involve both contralateral homologous and heterologous muscles with the greatest strength-training responses from high-load/low-repetition training.

Evidence of nonlocal muscle fatigue in male youth.

Evidence for nonlocal muscle fatigue (NLMF) has been inconsistent in adults, with no studies investigating youth. The objective was to examine NLMF in youth. Forty-two young males (age, 10-13 years) were tested for maximal voluntary isometric contraction (MVIC) force of the ipsilateral and contralateral knee extensors at 90° and 120° knee flexion, elbow flexors at 90°, handgrip, knee extensor isokinetic torque (300°·s-1 analyzed at 90° and 120° knee flexion), as well as a unilateral countermovement jump (CMJ) and Y Balance test (YBT). Isokinetic fatigue group (n = 15) had unilateral fatigue induced with 10 sets of 20 repetitions of maximal isokinetic knee extensor contractions at 300°·s-1. Isometric fatigue group (n = 15) used 10 repetitions of 6-s knee extensor MVIC whereas the control group (n = 12) were not fatigued. There was no significant difference in the response to the isometric- or isokinetic-fatigue intervention protocols. Main time effects indicated that NLMF was evident with the contralateral knee extensor MVIC at 90° (p = 0.008; 8.9%), knee extensor isokinetic torque at 90° (p < 0.001; 11.4%), and 120° (p = 0.05; 5.4%), CMJ (p = 0.02; 11.5%), handgrip (p = 0.06; 4.5%), elbow flexors (p < 0.001; 7.7%), and YBT (p = 0.001; 5.6%). Ipsilateral NLMF deficits occurred with handgrip (p < 0.001; 7.3%), elbow flexors MVICs (p < 0.001; 10.7%), CMJ (p = 0.02; 12.2%), and YBT (p = 0.002; 3.8%). NLMF with similar relative fatigue-induced deficits of fatigued and nonfatigued limbs suggest that youth fatigue is highly dependent upon the extent of activation or inhibition of the nervous system. Coaches of young athletes might consider developing technical motor skills before fatiguing exercise components, which might hinder the proficiency of their performance.

Comparison of static balance and the role of vision in elite athletes.

When prescribing balance exercises to athletes in different sports, it may be important to recognize performance variations. Indeed, how athletes from different sports perform on balance tests is not well understood. The goal of the present study was to compare static balance and the role of vision among elite sprinters, jumpers and rugby players. The modified clinical test of sensory interaction on balance (mCTSIB) was used to assess the velocity of the center-of-pressure (CoP) on a force platform during a 30 s bipedal quiet standing posture in 4 conditions: firm surface with opened and closed eyes, foam surface with opened and closed eyes. Three-factor ANOVA indicated a significant main effect for groups (F=21.69, df=2, p<0.001, η(2) = 0.34). Significant main effect of vision (F=43.20, df=1, p<0.001, η(2) = 0.34) and surface (F=193.41, df=1, p<0.001, η(2) = 0.70) as well as an interaction between vision (eyes open, eyes closed) and surface (firm and foam) (F=21.79, df=1, p=0.001) were reported in all groups. The subsequent Bonferroni-Dunn post hoc test indicated that rugby players displayed better static balance than sprinters and jumpers (p=0.001). The comparison of sprinters and jumpers did not reveal significant differences (p>0.05). The nature of the sport practiced and the absence of visual control are linked to modify static balance in elite athletes. Coaches and strength and conditioning professionals are recommended to use a variety of exercises to improve balance, including both exercises with opened and closed eyes on progressively challenging surfaces in order to make decisions about tasks and sensory availability during assessment and training.