the american college of sports medicine ( acsm ) recommends that healthy adults should participate in moderately intense aerobic exercise , defined as 64 
76% of one s maximal heart rate , for at least thirty minutes , five days per week .
this is considered the minimum threshold of aerobic exercise for one to maintain health and reduce risk for chronic disease .
this exercise may be attained through any number of different means , such as walking , jogging , swimming , or cycling .
these activities are likely the most popular and preferred methods of exercise as one can perform them for various durations , depending upon one s chosen exercise intensity .
another form of aerobic exercise in which people may participate to improve their health is repetitive jumping .
most people are likely familiar with repetitive jumping , as rope skipping or jumping rope is an activity often observed in elementary school children .
repetitive jumping is an intense activity where the heart rate will often rise quickly after as little as two minutes of jumping .
previous research has demonstrated that this type of activity can contribute to a substantial caloric expenditure as it elicits a high metabolic demand from both aerobic and anaerobic sources , and that regardless of jumping cadence there appears to be no difference in physiological stress . however , as these early studies were conducted with subjects turning and skipping a rope , the present study employed the use of a new exercise device specifically designed for repetitive jumping .
an innovative device ( the digi - jump ) has been developed which allows one to use jumping as a training technique without some of the limitations of jumping rope .
this device allows one to jump at a predetermined rate ( jumps per minute ) and at a pre - determined height per jump , while not having to utilize one s hands and arms , thus possibly reducing localized fatigue and enabling one to continue exercising longer and more consistently . also , as the jumping rate is governed by a series of lights and audible beeps , one may continue to exercise even if the person has an error . in traditional rope jumping ,
when the rope catches the foot , one must stop exercising and then start again .
this device has only recently been developed and is patent pending ( patent application # 10/464,373 ) .
the only previously published research employing this device was a 2008 study by sivley , et al . , which examined the test - retest reliability of this device .
( 2008 ) demonstrated that the digi - jump has test - retest reliability coefficients that are comparable to other commonly used exercise modalities ( absolute vo2 : 0.95 ; relative vo2 : 0.71 ; hr : 0.89 ; rpe : 0.75 ) . early research on rope skipping revealed no differences in metabolic demand between jumping at different cadences , nor did these studies employ a jumping cadence lower than 120 jumps per minute ( jpms ) .
however , those studies used a rope while the present study allowed the subjects arms to swing freely , and the present study also required subjects to jump at a lower cadence of 100 jpms . therefore , the purpose of this study was to investigate the difference in metabolic stress between repetitive jumping at 100 vs. 120 jpms on the digi - jump machine .
twenty - eight subjects ( 18 males and 10 females ) between the ages of 18 and 25 years voluntarily completed this study .
subjects were recruited from the local university and city community , and consisted of individuals who were already participating in at least 30 minutes of moderate recreational physical activity on most days of the week .
each subject completed a physical activity readiness questionnaire ( par - q ) and a health status questionnaire to screen for any health risk , and acsm guidelines were employed to eliminate any potential subjects with known risk factors .
subjects also understood and signed a written informed consent consistent with the requirements of the western kentucky university human subjects review board .
all jumping trials were conducted on a digi - jump machine . during both exercise trials ,
metabolic measurements were obtained using a two - way low - resistance breathing valve and a respiratory mask , which covered the mouth and nose .
expired gases were analyzed using a vacumed vista mini - cpx ( vacumed , ventura , ca ) .
a heart rate monitor was also worn during testing ( polar vantage xl , port washington , ny ) , and hr was monitored using telemetry .
carbon dioxide and oxygen analyzers were calibrated before each test , using calibration gases of known concentration .
the flowmeter was calibrated using a hans rudolph ( series 4900 ) 3.0 l calibration syringe ( kansas city , mo ) .
rating of perceived exertion ( rpe ) was determined at the end of each minute during each test , using borg s 15-point scale .
they were instructed to report for testing after refraining from strenuous activity for a minimum of 48 hours , and from caffeine , nicotine , and alcohol for a minimum of 24 hours . during the initial visit a thorough explanation of the study
was given , along with completion of initial screening procedures and instructions regarding subsequent lab sessions .
percent body fat was measured based on age , gender and the sum of three skinfold sites ( males : chest , abdomen , and thigh ; females : triceps , suprailiac , and thigh ) using lange skinfold calipers .
subjects were instructed to jump at the defined cadence until volitional exhaustion , or for a maximum of fifteen minutes .
the second visit consisted only of the remaining exercise trial ( 120 or 100 jpms ) .
jumping trials were performed on separate days in a counterbalanced order with a minimum of 48 hours rest between each . statistical package for the social sciences ( spss ) software was used to perform all analyses .
all data is reported as mean ( m ) + standard deviation ( sd ) .
analysis of variance ( anova ) was used to test for differences among subjects responses from the two exercise protocols .
twenty - eight subjects ( 18 males and 10 females ) between the ages of 18 and 25 years voluntarily completed this study .
subjects were recruited from the local university and city community , and consisted of individuals who were already participating in at least 30 minutes of moderate recreational physical activity on most days of the week .
each subject completed a physical activity readiness questionnaire ( par - q ) and a health status questionnaire to screen for any health risk , and acsm guidelines were employed to eliminate any potential subjects with known risk factors .
subjects also understood and signed a written informed consent consistent with the requirements of the western kentucky university human subjects review board .
all jumping trials were conducted on a digi - jump machine . during both exercise trials ,
metabolic measurements were obtained using a two - way low - resistance breathing valve and a respiratory mask , which covered the mouth and nose .
expired gases were analyzed using a vacumed vista mini - cpx ( vacumed , ventura , ca ) .
a heart rate monitor was also worn during testing ( polar vantage xl , port washington , ny ) , and hr was monitored using telemetry . carbon dioxide and oxygen analyzers were calibrated before each test , using calibration gases of known concentration .
the flowmeter was calibrated using a hans rudolph ( series 4900 ) 3.0 l calibration syringe ( kansas city , mo )
. rating of perceived exertion ( rpe ) was determined at the end of each minute during each test , using borg s 15-point scale .
they were instructed to report for testing after refraining from strenuous activity for a minimum of 48 hours , and from caffeine , nicotine , and alcohol for a minimum of 24 hours . during the initial visit a thorough explanation of the study
was given , along with completion of initial screening procedures and instructions regarding subsequent lab sessions .
percent body fat was measured based on age , gender and the sum of three skinfold sites ( males : chest , abdomen , and thigh ; females : triceps , suprailiac , and thigh ) using lange skinfold calipers .
subjects were instructed to jump at the defined cadence until volitional exhaustion , or for a maximum of fifteen minutes .
the second visit consisted only of the remaining exercise trial ( 120 or 100 jpms ) .
jumping trials were performed on separate days in a counterbalanced order with a minimum of 48 hours rest between each .
statistical package for the social sciences ( spss ) software was used to perform all analyses .
all data is reported as mean ( m ) + standard deviation ( sd ) .
analysis of variance ( anova ) was used to test for differences among subjects responses from the two exercise protocols .
subjects were lean ( body fat 13.6 + 5.6% ) and reported being recreationally active , but none were competitive athletes nor had any participated in a structured aerobic exercise or training program for a minimum of six months prior to the study .
tables 2 and 3 depict subjects metabolic responses to each jump cadence ( 120 jpm vs. 100 jpm ) used for this study .
table 2 reflects peak metabolic values for each trial , while table 3 displays average values for each trial . differences in both peak and average rer ( 1.08  .087 vs. 1.17  .1 p0.001 ; 0.99  .076 vs. 1.04  .098 p=0.002 , respectively ) were observed across the trials .
though rer values indicated that these protocols were both primarily anaerobic , the slower cadence ( 100 jpm ) appeared to be a significantly more strenuous activity .
differentiated rpe was collected each minute , and though total body rpe was not different for either peak or average analysis , differences were observed in peak rpe for the upper - leg ( 15.29  3.89 vs. 16.75  2.52 p=0.022 ) and in average rpe for the lower leg ( 15.04  2.55 vs. 13.94  2.02 p=0.019 ) .
subjects were able to exercise for a longer duration at 120 jpms compared to 100 jpms ( 12.4  3.42 mins vs. 9.68  4.31 mins p=.000 ) .
seventeen of the twenty - eight subjects completed the full fifteen minutes on the 120 jpm trial , while on seven of the twenty - eight completed fifteen minutes on the 100 jpm trial .
there were no differences observed in vo2 , hr , or total body rpe across trials .
the present study examined the differences in metabolic stress between jumping at 120 jpms compared to 100 jpms on the digi - jump machine .
statistics revealed that for both peak and mean values , subjects had similar vo2 , hr , and total body rpe values during the two trials
. however , for both peak and mean values , subjects showed a significantly different rer , with the 100 jpm trial being the more anaerobic of the two trials .
the 100 jpm trial also resulted in a significantly greater upper - leg rpe when considering only peak values .
lower - leg rpe was significantly higher for the 120 jpm trial when considering average values .
there was also a significant difference in trial duration , as subjects were able to sustain the 120 jpm trial longer than the 100 jpm trial .
considering the differences in rer and the fact that subjects were able to sustain longer the 120 jpm cadence , the similarities in vo2 and hr are intriguing .
while the subjects were not tested prior to the jumping trials for maximal oxygen uptake , it can be assumed that , based on age - predicted max heart rate and the average hr observed during the trials , that subjects exercised at approximately 80% of their max .
however , that might be an overestimation considering the peak and average vo2 values observed during the trials .
the subjects were college - aged , recreationally active college students , and if they reached 80% of max , then that would infer that their max vo2 would only average around 50 ml*kg*min , based on peak vo2 observed .
previous research on rope skipping reported exercise intensities of between 8  12 metabolic equivalents ( mets ) [ 3 , 5 , 6 , 11 ] , and these digi - jump trials , where jumping was done without a rope , elicited similar levels of exertion .
the significantly greater rer found with the 100 jpm trial is consistent with subjective comments provided by subjects following the trials .
all subjects commented that the 100 jpm trial was more difficult and resulted in more upper - leg fatigue , due probably to the difficulty in maintaining the slower cadence .
though contact time with the jumping platform was not measured , the subjects appeared to experience a protracted eccentric contraction , particularly in the quadriceps and hamstrings , due to the added deceleration required between jumps to follow the slower cadence . a rope skipping study by quirk and sinning ( 1979 ) did not measure rer , but did measure lactate , and their results revealed higher lactate values elicited from slower cadences .
our results are consistent with this finding in that the lower cadence ( 100 jpm ) had a greater anaerobic contribution as reflected through the rer measurement .
subjects were able to exercise approximately 25% longer during the 120 jpm trial compared to the 100 jpm trial .
however , subjects did report a significantly greater average lower - leg rpe from the faster 120 jpm cadence .
subjects comments seemed to suggest that this was due to fatigue in the anterior tibialis region and primarily the result of being able to exercise for a longer duration , thus greater localized fatigue .
post - trial comments were consistent in that while the faster , 120 jpm trial was preferred , it did result in more localized lower - leg fatigue and foot fatigue . a possible explanation for this observed phenomenon is both an increased duration compared with the 100 jpm trial in combination with a greater volume of jumps at the faster rate .
this study examined repetitive jumping at two different cadences on the digi - jump machine .
consistent with previous research on rope skipping , repetitive jumping without a rope is also a strenuous activity , regardless of jumping cadence .
however , it does appear that jumping at more rapid cadences is preferred and will allow for a more protracted exercise session .
future research in this area should focus on the effects of jumping on different surfaces and the role of repetitive jumping in bone and joint health .
 the american college of sports medicine ( acsm ) recommends that healthy adults achieve a minimum of thirty minutes of moderate intensity aerobic exercise five days per week . 
 while cycling , walking , and jogging are commonly observed methods of achieving these recommendations , another option may be repetitive jumping . 
 the purpose of this study was to examine the metabolic responses between repetitive jumping at a cadence of 120 jumps per minute ( jpms ) vs. 100 jpms when utilizing the digi - jump machine . 
 twenty - eight subjects completed two jumping trials , one at 120 jpms and one at 100 jpms . 
 subjects jumped until volitional exhaustion , or for a maximum of fifteen minutes . 
 oxygen uptake ( vo2 ) , heart rate ( hr ) , respiratory exchange ratio ( rer ) , and rating of perceived exertion ( rpe ) were assessed each minute of each exercise trial . 
 rpe was differentiated , in that subjects reported perceived exertion of their total body , their upper - leg , and their lower leg . 
 results of this study indicated that there was no significant difference between the two trials for vo2 , hr , or total body rpe . 
 differences were reported between trials for peak and average rer , with the 120 jpm trial eliciting a lower rer for both ( peak : 1.08  .087 vs. 1.17  .1 p=.000 ; average : .99  .076 vs. 1.04  .098 p=.002 ) , peak upper leg rpe ( 120 : 15.29  3.89 vs. 100 : 16.75  2.52 p=.022 ) , and average lower leg rpe ( 120 : 15.04  2.55 vs. 100 : 13.94  2.02 p=.019 ) . 
 also , there was a significant difference in exercise duration between the trials , with subjects able to exercise longer during the 120 jpm trial ( 12.4  3.42 mins vs. 9.68  4.31 mins p=.000 ) . 
 these data indicate that while the physiological stress may not be different between the two trials as indicated by vo2 and hr , the 120 jpm trial appears less strenuous as evidenced by rer values and by subjects ability to exercise longer at that cadence . 
INTRODUCTION
METHODS
Subjects
Instruments
Experimental Protocol
Statistical Analysis
RESULTS
DISCUSSION