***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background . Previous research has shown that children can increase their muscular strength and muscular endurance as a result of regular participation in a progressive resistance training program . However , the most effective exercise prescription regarding the number of repetitions remains question able . Objective . To compare the effects of a low repetition – heavy load resistance training program and a high repetition – moderate load resistance training program on the development of muscular strength and muscular endurance in children . Design . Prospect i ve , controlled trial . Setting . Community-based youth fitness center . Subjects . Eleven girls and 32 boys between the ages of 5.2 and 11.8 years . Intervention . In twice-weekly sessions of resistance training for 8 weeks , children performed 1 set of 6 to 8 repetitions with a heavy load ( n = 15 ) or 1 set of 13 to 15 repetitions with a moderate load ( n = 16 ) on child-size exercise machines . Children in the control group ( n = 12 ) did not resistance train . One repetition maximum ( RM ) strength and muscular endurance ( repetitions performed posttraining with the pretraining 1-RM load ) were determined on the leg extension and chest press exercises . Results . One RM leg extension strength significantly increased in both exercise groups compared with that in the control subjects . Increases of 31.0 % and 40.9 % , respectively , for the low repetition – heavy load and high repetition – moderate load groups were observed . Leg extension muscular endurance significantly increased in both exercise groups compared with that in the control subjects , although gains result ing from high repetition – moderate load training ( 13.1 ± 6.2 repetitions ) were significantly greater than those result ing from low repetition – heavy load training ( 8.7 ± 2.9 repetitions ) . On the chest press exercise , only the high repetition – moderate load exercise group made gains in 1-RM strength ( 16.3 % ) and muscular endurance ( 5.2 ± 3.6 repetitions ) that were significantly greater than gains in the control subjects . Conclusion . These findings support the concept that muscular strength and muscular endurance can be improved during the childhood years and favor the prescription of higher repetition – moderate load resistance training programs during the initial adaptation period Abstract Saeterbakken , AH and Fiml and , MS . Electromyographic activity and 6RM strength in bench press on stable and unstable surfaces . J Strength Cond Res 27(4 ) : 1101–1107 , 2013—The purpose of the study was to compare 6-repetition maximum ( 6RM ) loads and muscle activity in bench press on 3 surfaces , namely , stable bench , balance cushion , and Swiss ball .  Sixteen healthy , resistance-trained men ( age 22.5 ± 2.0 years , stature 1.82 ± 6.6 m , and body mass 82.0 ± 7.8 kg ) volunteered for 3 habituation/strength testing sessions and 1 experimental session . In r and omized order on the 3 surfaces , 6RM strength and electromyographic activity of pectoralis major , deltoid anterior , biceps brachii , triceps brachii , rectus abdominis , oblique external and erector spinae were assessed . Relative to stable bench , the 6RM strength was approximately 93 % for balance cushion ( p ⩽ 0.001 ) and approximately 92 % for Swiss ball ( p = 0.008 ) ; the pectoralis major electromyographic ( EMG ) activity was approximately 90 % using the balance cushion ( p = 0.080 ) and approximately 81 % using Swiss ball ( p = 0.006 ) ; the triceps EMG was approximately 79 % using the balance cushion ( p = 0.028 ) and approximately 69 % using the Swiss ball ( p = 0.002 ) . Relative to balance cushion , the EMG activity in pectoralis , triceps , and erector spinae using Swiss ball was approximately 89 % ( p = 0.016 ) , approximately 88 % ( p = 0.014 ) and approximately 80 % ( p = 0.020 ) , respectively . In rectus abdominis , the EMG activity relative to Swiss ball was approximately 69 % using stable bench ( p = 0.042 ) and approximately 65 % using the balance cushion ( p = 0.046 ) . Similar EMG activities between stable and unstable surfaces were observed for deltoid anterior , biceps brachii , and oblique external . In conclusion , stable bench press had greater 6RM strength and triceps and pectoralis EMG activity compared with the unstable surfaces . These findings have implication s for athletic training and rehabilitation , because they demonstrate an inferior effect of unstable surfaces on muscle activation of prime movers and strength in bench press . If an unstable surface in bench press is desirable , a balance cushion should be chosen instead of a Swiss ball Stability ball training ( SBT ) is believed to improve spinal stability ( SS ) and could reduce the risk of back pain in sedentary individuals . The purpose of this study was to examine the effects of SBT on SS .  Twenty sedentary individuals were r and omly assigned to either an experimental group that performed SBT twice per week for 10 weeks or to a control group . Differences between groups were assessed by analysis of variance ( ANOVA ) with repeated measures . The experimental group improved significantly ( p < 0.05 ) on the static back-endurance test from pretest ( 149.3 ± 72.3 seconds ) to posttest ( 194.6 ± 56.7 seconds ) and the side bridge test from pretest ( 45.4 ± 39.4 seconds ) to posttest ( 71.3 ± 59.7 seconds ) . Back endurance for the control group did not change from pretest ( 123.4 ± 64.9 seconds ) to posttest ( 87.5 ± 40.2 seconds ) , nor did the results of the side bridge test change for this group from pretest ( 41.8 ± 26.4 seconds ) to posttest ( 51.6 ± 35.9 seconds ) . These findings illustrate that SBT may provide improvements in SS within this population . Practitioners might use SBT exercises where the position of the spine is maintained during the early phases of back-pain prevention programs . This type of programming might be beneficial to individuals who spend a good deal of time sitting ( i.e. , in corporate fitness programs ) or for individuals who are prone to back pain and have been cleared to exercise . Also , the side bridge and static back endurance assessment s may be good choices for measuring SS in field setting Abstract Saeterbakken , AH and Finl and , MS . Muscle force output and electromyographic activity in squats with various unstable surfaces . J Strength Cond Res 27(1 ) : 130–136 , 2013—The purpose of the study was to compare force output and muscle activity of leg and trunk muscles in isometric squats executed on stable surface ( i.e. , floor ) , power board , BOSU ball , and balance cone . Fifteen healthy men ( 23.3 ± 2.7 years , mass : 80.5 ± 8.5 kg , height : 1.81 ± 0.09 m ) volunteered .  The force output and electromyographic ( EMG ) activities of the rectus femoris , vastus medialis , vastus lateralis , biceps femoris , soleus , rectus abdominis , oblique external , and erector spinae were assessed . The order of the surfaces was r and omized . One familiarization session was executed before the experimental test . Compared with stable surface ( 749 ± 222 N ) , the force output using power board was similar ( −7 % , p = 0.320 ) but lower for BOSU ball ( −19 % , p = 0.003 ) and balance cone ( −24 % , p ⩽ 0.001 ) . The force output using BOSU ball and balance cone was approximately 13 % ( p = 0.037 ) and approximately 18 % ( p = 0.001 ) less than the power board . There were similar EMG activities between the surfaces in all muscles except for rectus femoris , in which stable squat provided greater EMG activity than did the other exercises ( p = 0.004–0.030 ) . Lower EMG activity was observed in the rectus femoris using balance cone compared with the BOSU ball ( p = 0.030 ) . In conclusion , increasing the instability of the surface during maximum effort isometric squats usually maintains the muscle activity of lower-limb and superficial trunk muscles although the force output is reduced . This suggests that unstable surfaces in the squat may be beneficial in rehabilitation and as a part of periodized training programs , because similar muscle activity can be achieved with reduced loads Background It has been demonstrated that core strength training is an effective means to enhance trunk muscle strength ( TMS ) and proxies of physical fitness  in youth . Of note , cross-sectional studies revealed that the inclusion of unstable elements in core strengthening exercises produced increases in trunk muscle activity and thus provide potential extra training stimuli for performance enhancement . Thus , utilizing unstable surfaces during core strength training may even produce larger performance gains . However , the effects of core strength training using unstable surfaces are unresolved in youth . This r and omized controlled study specifically investigated the effects of core strength training performed on stable surfaces ( CSTS ) compared to unstable surfaces ( CSTU ) on physical fitness in school-aged children . Methods Twenty-seven ( 14 girls , 13 boys ) healthy subjects ( mean age : 14 ± 1 years , age range : 13–15 years ) were r and omly assigned to a CSTS ( n = 13 ) or a CSTU ( n = 14 ) group . Both training programs lasted 6 weeks ( 2 sessions/week ) and included frontal , dorsal , and lateral core exercises . During CSTU , these exercises were conducted on unstable surfaces ( e.g. , TOGU © DYNAIR CUSSIONS , THERA-B AND © STABILITY TRAINER ) . Results Significant main effects of Time ( pre vs. post ) were observed for the TMS tests ( 8 - 22 % , f = 0.47 - 0.76 ) , the jumping sideways test ( 4 - 5 % , f = 1.07 ) , and the Y balance test ( 2 - 3 % , f = 0.46 - 0.49 ) . Trends towards significance were found for the st and ing long jump test ( 1 - 3 % , f = 0.39 ) and the st and - and -reach test ( 0 - 2 % , f = 0.39 ) . We could not detect any significant main effects of Group . Significant Time x Group interactions were detected for the st and - and -reach test in favour of the CSTU group ( 2 % , f = 0.54 ) . Conclusions Core strength training result ed in significant increases in proxies of physical fitness in adolescents . However , CSTU as compared to CSTS had only limited additional effects ( i.e. , st and - and -reach test ) . Consequently , if the goal of training is to enhance physical fitness , then CSTU has limited advantages over CSTS.Trial registration Clinical Trials.gov Identifier : NCT02290457 Registered 13 November 2014 The purpose of this study was to compare the effects of 5 weeks of physioball core stability and balance exercises with conventional floor exercises in women . The experimental group ( n = 15 ) performed curl-ups and back extensions on the physioball while the control group ( n = 15 ) performed the same exercises on the floor . Baseline and post-training tests included electromyography ( EMG ) recordings of the rectus abdominus and erector spinae muscles ; abdominal , back , and knee strength measurements with the Cybex Norm System ; and 2 unilateral stance balance tests . The physioball group was found to have significantly greater mean change in EMG flexion and extension activity ( p = 0.04 and p = 0.01 , respectively ) and greater balance scores ( p < 0.01 ) than the floor exercise group . No significant changes ( p > 0.05 ) were observed for heart rate or Cybex strength measurements . Early adaptations in a short-term core exercise program using the physioball result ed in greater gains in torso balance and EMG neuronal activity in previously untrained women when compared to performing exercises on the floor Background : Age-related postural misalignment , balance deficits and strength/power losses are associated with impaired functional mobility and an increased risk of falling in seniors .  Core instability strength training ( CIT ) involves exercises that are challenging for both trunk muscles and postural control and may thus have the potential to induce benefits in trunk muscle strength , spinal mobility and balance performance . Objective : The objective was to investigate the effects of CIT on measures of trunk muscle strength , spinal mobility , dynamic balance and functional mobility in seniors . Methods : Thirty-two older adults were r and omly assigned to an intervention group ( INT ; n = 16 , aged 70.8 ± 4.1 years ) that conducted a 9-week progressive CIT or to a control group ( n = 16 , aged 70.2 ± 4.5 years ) . Maximal isometric strength of the trunk flexors/extensors/lateral flexors ( right , left)/rotators ( right , left ) as well as of spinal mobility in the sagittal and the coronal plane was measured before and after the intervention program . Dynamic balance ( i.e. walking 10 m on an optoelectric walkway , the Functional Reach test ) and functional mobility ( Timed Up and Go test ) were additionally tested . Results : Program compliance was excellent with participants of the INT group completing 92 % of the training sessions . Significant group × test interactions were found for the maximal isometric strength of the trunk flexors ( 34 % , p 
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In addition , large effects were detected on strength endurance in adolescents and in young adults ; in old adults , a small effect was found .
With regard to muscle power , medium effects were observed in young adults and small effects were observed in old adults .
Further , large effects were found for static and dynamic balance in old adults , but only a small effect was found for dynamic balance in young adults .
The comparison of STU and STS revealed inconsistent results as indicated by training-induced changes in favour of STU , as well as STS .
Small to medium effects were found for maximal strength in adolescents in favour of STS , and small effects were found in young adults in favour of STU .
With regard to strength endurance , large effects were found in adolescents in favour of STS and small effects were found in favour of STU .
Additionally , we detected small effects in young adults in favour of STU .
In terms of muscle power , no effects were observed in adolescents but medium effects were found in favour of STS in young adults .
With regard to balance , small effects were detected in adolescents for static and dynamic balance in favour of STU .
In young adults , small effects were found for static balance in favour of STS .
With regard to dynamic balance , the analysis revealed small effects in young adults in favour of STU .
Conclusions Compared with CON , STU is effective in improving muscle strength , power and balance in adolescents , young adults and old adults .
However , inconsistent results were particularly found in adolescents and young adults when the specific effects of STU were compared with those of STS .
We conclude that the performance of STU compared with STS has limited extra effects on muscle strength , power and balance performance in healthy adolescents and young adults .
Given that our systematic search did not identify studies that examined the effects of STU versus STS in children , middle-aged adults and old adults , further research of high method ological quality is needed to determine whether there are additive effects of STU as compared with STS in those age groups