***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: The purpose of this study was to test the torque generating capabilities of three commercially available neuromuscular electrical stimulators ( NMES ) having different current characteristics . Twenty healthy adults were positioned in sitting on an isokinetic dynamometer . Maximum voluntary isometric knee extension torque was determined . Subsequently , two 10-sec , maximally tolerated contractions were elicited with each machine . The order of stimulation was r and omized and there were 2-minute rest periods between contractions . Electrically elicited torque values were expressed as a percentage of the maximal voluntary isometric torque ( % MVIT ) . Analysis of variance with one repeated measure showed a significant difference among % MVIT produced by the stimulators . NMES 2 ( Nemectrodyn 7 ) produced significantly less % MVIT than either NMES 1 ( Electrostim 180 - 2 ) or NMES 3 ( Chattanooga VMS ) . In all but three cases , NMES 2 's maximal current output was reached . Although all three devices were capable of producing % MVIT that has been shown to be sufficient for strengthening , it appears that NMES 2 does not have the capacity to provide " overload " as strength increases . J Orthop Sports Phys Ther 1989;10(8):297 - 301 The aim of the study was to investigate the uniformity of the muscle motor point location for lower limb muscles in healthy subjects . Fifty-three subjects of both genders ( age range : 18–50 years ) were recruited . The muscle motor points were identified for the following ten muscles of the lower limb ( dominant side ) : vastus medialis , rectus femoris , and vastus lateralis of the quadriceps femoris , biceps femoris , semitendinosus , and semimembranosus of the hamstring muscles , tibialis anterior , peroneus longus , lateral and medial gastrocnemius . The muscle motor point was identified by scanning the skin surface with a stimulation pen electrode and corresponded to the location of the skin area above the muscle in which an electrical pulse evoked a muscle twitch with the least injected current . For each investigated muscle , 0.15 ms square pulses were delivered through the pen electrode at low current amplitude ( < 10 mA ) and frequency ( 2 Hz ) . 16 motor points were identified in the 10 investigated muscles of almost all subjects : 3 motor points for the vastus lateralis , 2 motor points for rectus femoris , vastus medialis , biceps femoris , and tibialis anterior , 1 motor point for the remaining muscles . An important inter-individual variability was observed for the position of the following 4 out of 16 motor points : vastus lateralis ( proximal ) , biceps femoris ( short head ) , semimembranosus , and medial gastrocnemius . Possible implication s for electrical stimulation procedures and electrode positioning different from those commonly applied for thigh and leg muscles are discussed This study compared between alternating and pulsed current electrical muscle stimulation ( EMS ) for muscle oxygenation and blood volume during isometric contractions . Nine healthy men ( 23–48 years ) received alternating current EMS ( 2500 Hz ) modulated at 75 Hz on the knee extensors of one leg , and pulsed current EMS ( 75 Hz ) for the other leg separated by 2 weeks in a r and omised , counter-balanced order . Pulse duration ( 400 μs ) , on – off ratio ( 5–15 s ) and other stimulation parameters were matched between conditions and 30 isometric contractions were induced at the knee joint angle of 100 ° ( 0 ° full extension ) . Changes in tissue oxygenation index ( ∆TOI ) and total hemoglobin volume ( ∆tHb ) of vastus lateralis and medialis muscles over 30 contractions were assessed by a near-infrared spectroscopy , and were compared between conditions by a two-way repeated measures ANOVA . Peak torque produced during EMS  increased over 30 contractions in response to the increase in the stimulation intensity for pulsed current , but not for the alternating current EMS . The torque during each isometric contraction was less stable in alternating than pulsed current EMS .  The changes in ∆TOI amplitude during relaxation phases and ∆tHb amplitude were not significantly different between conditions . However , the decreases in ∆TOI amplitude during contraction phases from baseline were significantly ( P < 0.05 ) greater for the pulsed current than alternating current from the 18th contraction ( −15.6 ± 2.3 vs. −8.9 ± 1.8 % ) to 30th contraction ( −10.7 ± 1.8 vs. −4.8 ± 1.5 % ) . These results suggest that the muscles were less activated in the alternating current EMS when compared with the pulsed current EMS BACKGROUND AND PURPOSE Neuromuscular electrical stimulation is used by physical therapists to improve muscle performance . Optimal forms of stimulation setting s are yet to be determined , as are possible sex-related differences in responsiveness to electrical stimulation . The objectives of the study were : ( 1 ) to compare the ability of 3 different waveforms to generate isometric contractions of the quadriceps femoris muscles of individuals without known impairments , ( 2 ) to compare muscle fatigue caused by repeated contractions induced by these same waveforms , and ( 3 ) to examine the effect of sex on muscle force production and fatigue induced by electrical stimulation . SUBJECTS Fifteen women and 15 men ( mean age=29.5 years , SD=5.4 , range=22 - 38 ) participated in the study . METHODS A portable battery-operated stimulator was used to generate either a monophasic or biphasic rectangular waveform . A stimulator that was plugged into an electrical outlet was used to generate a 2,500-Hz alternating current . Phase duration , frequency , and on-off ratios were kept identical for both stimulators . Participants did not know the type of waveform being used . Torque was measured using a computerized dynamometer . A maximal voluntary isometric contraction ( MVIC ) of the right quadriceps femoris muscle set at 60 degrees of knee flexion was determined during the first session . In each of the 3 testing sessions , torque of contraction and fatigue elicited by one waveform were measured . Order of testing was r and omized . Torque elicited by electrical stimulation was expressed as a percentage of average MVIC . A mixed-model analysis of variance was used to determine the effect of stimulation and sex on strength of contraction and fatigue . Bonferroni-corrected post hoc tests were used to further distinguish between the effects of the 3 stimulus waveforms . RESULTS The results indicated that the monophasic and biphasic waveforms generated contractions with greater torque than the polyphasic waveform . These 2 waveforms also were less fatiguing . The torques from the maximally tolerated electrically elicited contractions were greater for the male subjects than for the female subjects . DISCUSSION AND CONCLUSION Muscle torque and fatigue of electrically induced contractions depend on the waveform used to stimulate the contraction , with monophasic and biphasic waveforms having an advantage over the polyphasic waveform . All tested waveforms elicited , on average , stronger contractions in male subjects than in female subjects when measured as a percentage of MVIC Objective The aim of this study was to investigate the effect of neuromuscular electrical stimulation burst duty cycle ( BDC ) and current type ( sinusoidal alternating current [ sAC ] vs. rectangular alternating current [ rAC ] ) on the electrically induced isometric torque ( EIT ) and discomfort .  Pulsed current ( PC ) stimulation , which corresponds to one pulse rAC , was included in testing . Design A repeated- measures design was used . The left quadriceps of 22 healthy subjects ( mean ± SD age , 33 ± 8 yrs ) were stimulated alternately with sAC and rAC current bursts ( 4-kHz carrier frequency ; 71 bursts per second burst frequency ) to produce isometric contractions . A range of BDCs were tested for sAC ( 7%–50 % ) and rAC ( 2%–18 % ) stimulation at fixed intensities while EIT and discomfort were recorded . BDC presentation order was r and omized . Results Overall , both current types elicited peak EIT at ∼14 % BDC ( range , 7%–21 % ) . Significantly more EIT was produced by rAC than by sAC stimulation ( P < 0.005 ) . Discomfort increased with BDC and was similar for both current types . Conclusions The study confirmed previous findings that conventional sAC stimulation ( 50 % BDC ) and pulsed current stimulation ( rAC with 2 % BDC ) used in sports and rehabilitation produce similar EIT levels . However , rAC stimulation at low BDC ( 7%–18 % ) was more effective ( + 35 % torque produced with similar discomfort ) than pulsed current or conventional sAC Background and Purpose . A r and omized controlled trial to compare 2 forms of monophasic pulsed currents with 2 forms of burst-modulated , kilohertz-frequency alternating current ( “ Russian current ” and “ Aussie current ” ) was conducted to establish whether different amounts of wrist extensor torque were produced and whether discomfort varied with stimulus type . Subjects . The 32 subjects were adults who were healthy and were drawn from a population of staff and students at La Trobe University . Methods . Each subject received all 4 currents . Maximal electrically induced torque ( MEIT ) of the wrist extensors was measured for each stimulus type . Relative discomfort of stimulation also was assessed . Results . Russian current elicited lower mean torque than those elicited by Aussie current and monophasic pulsed currents . The Russian and Aussie currents elicited significantly less discomfort than the 2 monophasic pulsed currents . Discussion and Conclusion . When force production and relative discomfort were jointly used as the criteria , Aussie current was found to be more effective than either of the monophasic pulsed currents or Russian current stimulation In the GRADE approach , r and omized trials start as high- quality evidence and observational studies as low- quality evidence , but both can be rated down if a body of evidence is associated with a high risk of publication bias . Even when individual studies included in best- evidence summaries have a low risk of bias , publication bias can result in substantial overestimates of effect . Authors should suspect publication bias when available evidence comes from a number of small studies , most of which have been commercially funded . A number of approaches based on examination of the pattern of data are available to help assess publication bias . The most popular of these is the funnel plot ; all , however , have substantial limitations . Publication bias is likely frequent , and caution in the face of early results , particularly with small sample size and number of events , is warranted The aim of the study was to investigate the influence of two different transcutaneous neuromuscular electrical stimulation procedures on evoked muscle torque and local tissue oxygenation . In the first one ( MP mode ) , the cathode was facing the muscle main motor point and stimulus amplitude was set to the level eliciting the maximal myoelectrical activation according to the amplitude of the evoked electromyogram ( EMG ) ; in the second one ( RC mode ) , the electrodes were positioned following common reference charts for electrode placement while stimulus amplitude was set according to subject tolerance . Tibialis Anterior ( TA ) and Vastus Lateralis ( VL ) muscles of 10 subjects ( 28.4 ± 8.2 years ) were tested in specific dynamometers to measure the evoked isometric torque . The EMG and near-infrared spectroscopy probes were placed on muscle belly to detect the electrical activity and local metabolic modifications of the stimulated muscle , respectively . The stimulation protocol consisted of a gradually increasing frequency ramp from 2 to 50 Hz in 7.5 s. Compared to RC mode , in MP mode the contractile parameters ( peak twitch , tetanic torque , area under the torque build-up ) and the metabolic solicitation ( oxygen consumption and hyperemia due to metabolites accumulation ) result ed significantly higher for both TA and VL muscles . MP mode result ed also to be more comfortable for the subjects . Based on the assumption that proper mechanical and metabolic stimuli are necessary to induce muscle strengthening , our results witness the importance of an optimized , i.e. , comfortable and effective , stimulation to promote the aforementioned muscle adaptive modifications OBJECTIVE : To test the feasibility of creating a valid and reliable checklist with the following features : appropriate for assessing both r and omised and non-r and omised studies ; provision of both an overall score for study quality and a profile of scores not only for the quality of reporting , internal validity ( bias and confounding ) and power , but also for external validity . DESIGN : A pilot version was first developed , based on epidemiological principles , review s , and existing checklists for r and omised studies . Face and content validity were assessed by three experienced review ers and reliability was determined using two raters assessing 10 r and omised and 10 non-r and omised studies . Using different raters , the checklist was revised and tested for internal consistency ( Kuder-Richardson 20 ) , test-retest and inter-rater reliability ( Spearman correlation coefficient and sign rank test ; kappa statistics ) , criterion validity , and respondent burden . MAIN RESULTS : The performance of the checklist improved considerably after revision of a pilot version . The Quality Index had high internal consistency ( KR-20 : 0.89 ) as did the subscales apart from external validity ( KR-20 : 0.54 ) . Test-retest ( r 0.88 ) and inter-rater ( r 0.75 ) reliability of the Quality Index were good . Reliability of the subscales varied from good ( bias ) to poor ( external validity ) . The Quality Index correlated highly with an existing , established instrument for assessing r and omised studies ( r 0.90 ) . There was little difference between its performance with non 
    Output:
    
Conclusions This meta- analysis does not establish that KFAC is superior to PC in increasing muscle-evoked torque and lessening discomfort level .