Short vs. Long Bouts of All-Out Rope Skipping: Effects on Metabolic and Perceptual Responses

Abstract

Rope skipping has been well documented for eliciting positive effects on various health outcomes and contributing to overall physical activity levels. However, the specific health benefits may depend on the duration and intensity of the exercise bouts. This study aimed to compare the (1) metabolic and (2) perceptual responses between short (30 s) and long (3 min) bouts of all-out rope skipping, and to (3) evaluate the reliability and validity of a newly invented electronic rope (E-rope). A total of 23 young adults (13 males and 10 females; aged 23.23 ± 2.62 y) repeated short and long skipping bouts on two testing days. The oxygen consumption ($\stackrel{·}{\mathrm{V}}$O₂), peak respiratory exchange ratio (RER), heart rate (HR), rate of perceived exertion (RPE), and post-exercise muscle soreness were assessed during each trial. Longer skipping bouts (148.33 skips·min⁻¹) resulted in significantly greater metabolic responses (p < 0.01, d = 1.00–3.27), higher rates of perceived exertion (p < 0.01, d = 2.28), and more post-exercise muscle soreness (p < 0.01, d = 0.66–1.49) compared to shorter bouts (165.83 skips·min⁻¹). The E-rope demonstrated sufficient concurrent validity (r > 0.9) and between-day reliability (ICC_3,1 = 0.89–0.95) but slightly overestimated the number of skips. Both long and short all-out skipping bouts were considered moderate-to-vigorous exercise, but longer bouts resulted in higher metabolic and perceptual demands. These findings may be useful for practitioners to strategically apply different skipping bouts to improve physical activity levels and facilitate training adaptation. The E-rope could serve as a self-monitoring and self-evaluating tool.

1. Introduction

High-intensity interval training (HIIT) is a popular exercise modality that requires maximum or nearly maximum effort in a shorter amount of time. Including sprints and all-out efforts in HIIT programs has also been shown to be effective practice [1] for team sports athletes [2], runners [3], and rowers [4]. The exercise bouts can be short (e.g., less than 45 s), or long, ranging from two to four minutes [5]. Different durations of HIIT have been shown to elicit various acute metabolic responses using certain modalities of exercise [5]. Despite the common practice and great potential of adopting rope skipping in HIIT, the metabolic responses during all-out rope skipping are still unclear.

Rope skipping is a commonly adopted exercise in athletic training and physical activity promotion. It has been used as plyometric training in strength and conditioning [6], and it is one of the most recommended exercise choices for cross-training or HIIT due to its portability and minimal equipment requirements. In a recent meta-analysis [7], jump training was found to improve the running speed for endurance runners by reducing the ground contact time during running. In fact, five-minute regular rope skipping has been suggested as a favorable warm-up protocol to enhance running endurance [8] and horizontal jumping capacity [9].

Rope skipping has been widely adopted in promoting physical fitness and physical activity levels among different populations of all ages and nations [10,11,12]. The metabolic equivalent of task (MET) is used as a reference threshold of absolute intensity (i.e., light: <3.00 METs; moderate: 3.00–5.99 METs; vigorous: ≥6.00 METs) [13,14], and the mean METs of prolonged rope skipping range from 8.00 METs in adults [15] to 10.10 METs in adolescents [16]. Recent rope-skipping competitions, such as 30 s single rope speed sprints and three-minute single rope speed endurance, are popular worldwide. However, the specific demands of each variation of rope-skipping bouts need to be understood to achieve the desired training adaptation. Increasing the skipping rate of standardized five-minute rope skipping from 125 to 145 skips∙min⁻¹ could result in oxygen consumption ($\stackrel{·}{\mathrm{V}}$O₂) with a small effect size (ES) (Cohen’s d = 0.27) [17]. Getchell and Cleary [18] recruited 10 participants and demonstrated that 66% of their maximal oxygen consumption ($\stackrel{·}{\mathrm{V}}$O_2max) was attained in the last minute of a 6.5 min rope-skipping bout at a speed of about 80 skips∙min⁻¹. Jumping at a higher rate of 138 skips∙min⁻¹, varying jumping techniques from alternate foot to crossover, could increase the $\stackrel{·}{\mathrm{V}}$O₂ from 30.8 mL∙kg⁻¹∙min⁻¹ (41.9% of $\stackrel{·}{\mathrm{V}}$O_2max) to 40.4 mL∙kg⁻¹∙min⁻¹ (56.4% of $\stackrel{·}{\mathrm{V}}$O_2max) [19]. Notably, these investigations of energy expenditure were limited to the submaximal intensity at assigned cadences.

Therefore, the first purpose of the present study was to investigate the two typical international rope-skipping speed events (i.e., all-out two-foot skipping for 30 s (Skip-30 s) and three minutes (Skip-3 min)) among apparently healthy young adults. We hypothesized that Skip-3 min would require higher physical demands in terms of the $\stackrel{·}{\mathrm{V}}$O₂, respiratory exchange ratio (RER), and heart rate (HR) response. Individuals perceive the intensity of exercise differently, and their effort perception may influence their behaviors [20]. Another important consideration is how perceptual measures, such as the rate of perceived exertion (RPE) and muscle soreness, are impacted by the two rope-skipping bouts. Consequently, the second purpose of this study was to compare the differences in perceptual responses between Skip-30 s and Skip-3 min.

In addition, in the recent digital era, technology can potentially serve the purpose of remote training when coaches and strength and conditioning coaches are absent. Some commercial electronic ropes (E-ropes) are equipped with digital counters, which usually count the number of loops completed. Nevertheless, the International Jump Rope Union (IJRU) determined successful skips by counting every completed right-foot jump. Although most commercial E-ropes claim that they count the number of jumps precisely, due to the varied definitions of a successful skip, the accuracy of such technology is in doubt. Consequently, the third purpose of the present study was to examine the reliability and validity of the self-counting function of the adopted E-rope, compared with the criterion of the IJRU. It was hypothesized that the counts by the E-rope would align with those by a rope-skipping judge recognized by the IJRU.

2. Materials and Methods

2.1. Experimental Approach to the Problem

This study adopted a within-subject design with repeated measures to examine the physiological and perceptual responses to Skip-30 s and Skip-3 min, as well as to assess the reliability and validity of the E-rope. The testing consisted of two sessions to evaluate the between-day reliability. Gaseous exchange data during and subjective feelings after the rope-skipping events were recorded. The rope-skipping performance was video-recorded for an IJRU-recognized judge to calculate the number of skips. Participants’ $\stackrel{·}{\mathrm{V}}$O_2max was measured by a treadmill running test to indicate their cardiovascular fitness. To maintain blindness during data collection, the entire process was completed by an independent research assistant.

2.2. Participants

The sample size was estimated using the G*Power software package (version 3.1.9.7, Franz Faul, University of Kiel, Kiel, Germany). In the current study, assuming a two-tailed alpha level of 0.05 and statistical power of 0.80 for a paired-sample t-test using an effect size of 0.70, the minimum sample size required was 19. We anticipated a dropout rate of 15–20%; therefore, from July 2021 to Dec 2021, 23 individuals (13 males and 10 females; for demographic information and physical capacity, see

Table 1. Descriptive statistics of the participants.

Variables	Participants	Mean (SD)
Sex (male: female)	n = 23	13: 10
Age (years)	n = 23	23.23 (2.62)
Height (cm)	n = 23	169.18 (8.63)
Weight (kg)	n = 23	62.21 (11.10)
Rope-skipping experience (years)	n = 23	5.09 (6.00)
$\stackrel{·}{\mathrm{V}}$O2max (mL·min−1·kg−1)	* n = 22	49.39 (6.93)

Note: $\stackrel{·}{\mathrm{V}}$O_2max, maximal oxygen consumption. * Data lost due to equipment failure (n = 22).

), who were familiarized with double-leg rope skipping, were recruited through the university’s electronic communication system and in person. The inclusion criteria were injury-free and at least 18 years old. Informed written consent was obtained from all participants involved in the study. They were fully informed of the potential benefits and risks of participating in this study, and that they could withdraw from the study at any time without any consequences. The study was conducted in accordance with the Declaration of Helsinki, and ethical approval of this research was obtained from the Human Research Ethics Committee of the university (reference no.: 2020-2021-0372).

2.3. Procedures

Each participant was invited to the university laboratory twice, with at least 48 h in between to allow for the washout effect. Anthropological data and rope-skipping performances were obtained. The participants were informed to avoid exhaustive physical activity four hours beforehand and to have a meal or snack an hour before their sessions. Participants received identical E-ropes and adjusted their lengths according to their heights. Participants stood on the midpoint of the rope, pulled the handles towards the chest, and lengthened or shortened the rope if necessary. Minor length adjustments were allowed after a few trials. A 15 min rope-skipping warm-up was then performed. Familiarization was permitted. See Figure 1 for the flow of the testing.

The rope-skipping performances Skip-30 s and Skip-3 min were then assessed on a hard and smooth floor at the laboratory in the university. Five-minute passive recovery was allowed in between. In the two visits, the rope-skipping tests were assessed using identical sequential order: Skip-30 s then Skip-3 min, which is a common order in a rope-skipping competition. Participants’ metabolic responses during the rope-skipping tests and perceptual measures were assessed in the second visit, followed by a $\stackrel{·}{\mathrm{V}}$O_2max treadmill test.

$\stackrel{·}{\mathrm{V}}$O_2max. Measuring a participant’s $\stackrel{·}{\mathrm{V}}$O_2max on a treadmill can provide important information about their aerobic fitness level and allow for a more comprehensive evaluation of their physical abilities. In this study, $\stackrel{·}{\mathrm{V}}$O_2max was examined using the Bruce protocol on an incremental motorized treadmill (Pulsar 3p, HP Cosmos, Nussdorf-Traunstein, Germany) with a chest-belt-system safety arch harness. This protocol is a standard, common, feasible, and reliable $\stackrel{·}{\mathrm{V}}$O_2max assessment without adverse effects on participants [21]. It consisted of multiple stages, each lasting three minutes to achieve a steady state in the exercise heart rate before the workload was increased. For each stage, the workload was controlled by speed and gradient. The speeds were set as 1.7, 2.5, 3.4, 4.2, 5, 5.5, and 6 mph, while the gradient rose 2% in each stage, starting from 10% at stage 1. Participants walked or ran at fixed speeds and gradients in each stage. The test ended and the participants’ $\stackrel{·}{\mathrm{V}}$O_2max was achieved after completing two of the following criteria: (a) participants’ volitional exhaustion; (b) RER ≥ 1.15 and/or (c) $\stackrel{·}{\mathrm{V}}$O₂ ≤ 2 mL∙kg⁻¹∙min⁻¹ after progressing to the subsequent stage. Participants’ $\stackrel{·}{\mathrm{V}}$O_2max during the test was directly measured using the COSMED K4b2 Portable Metabolic Measurement System (COSMED S.r.l., Pavona di Albano, Rome, Italy).

Rope-Skipping Performance. The participants were encouraged to complete the rope-skipping tests with maximal effort according to the respective timing tracks [22]. During the tests, the E-rope counted the number of loops it completed. Meanwhile, two iPads (6th generation, iOS 14.4) were set to videotape (using 120 frames·s⁻¹) the events, and the numbers of skips were counted by a rope-skipping judge recognized by the IJRU afterwards. In this study, basic two-foot jumps were performed, and successful skips were calculated according to the official rules. The counts by the judge were compared with the E-rope self-counting records and were used for further calculations (e.g., for energy expenditure).

Metabolic Responses. On the second visit, HR responses of Skip-30 s and Skip-3 min were recorded by a Polar Vantage NV chest-strap HR monitor (Polar Electro Oy, Kempele, Finland). Pulmonary gas exchange and $\stackrel{·}{\mathrm{V}}$O₂ during exercise were also measured by the COSMED K4b2 Portable Metabolic Measurement System (COSMED S.r.l., Pavona di Albano, Rome, Italy) (Figure 2). Excellent reliability of this device in measuring $\stackrel{·}{\mathrm{V}}$O_2max was demonstrated (ICC = 0.97) [23]. The RER was calculated by breath-by-breath data.

Perceptual Measures. The Borg RPE and muscle soreness [24] after each rope-skipping test were recorded on the 2nd visit. The RPE scale ranged from 6 (no exertion) to 20 (maximal exertion). The muscle soreness questionnaire enquired about nine major muscle groups on both sides of the body using a scale from 1 (feeling great) to 5 (very sore), with 0.5-point increments allowed. To analyze the data, the average soreness score was calculated for each muscle group on both sides of the body. A measure of lower body muscle soreness was derived by summing the soreness scores for the left and right quadriceps, groin, calves, hamstrings, and gluteus muscles. Similarly, a measure of upper body soreness was calculated by averaging the soreness scores for the left and right chest, shoulder, lower back, and upper back muscles.

2.4. Statistical Analyses

Descriptive statistics were reported as means (standard deviations) and other descriptions where specified. The normality of data was checked by the Shapiro–Wilk test and histograms. Rope-skipping metabolic and perceptual demands in Skip-30 s and Skip-3 min were also compared by multiple paired-sample t-tests. Test–retest reliabilities were assessed by multiple intraclass correlation coefficient (ICC) analyses, single-measure two-way mixed absolute agreement parameters (ICC_3,1) [25], and the coefficient of variation (CV). ICC_3,1 was classified as moderate (0.50–0.75), good (>0.75), and excellent (>0.9) [26]. The CV can reveal the magnitude of the measurement error, which was categorized as good (<5%), moderate (5–10%), and poor (>10%). Sufficient reliability can be illustrated by ICC ≥ 0.75 and CV ≤ 10%. Minimal detectable change (MDC) and standard error of measurement (SEM) were also calculated. Absolute and relative agreements between counting by E-rope and the IJRU judge were assessed by paired-sample t-test and Pearson correlation coefficient (r), respectively. ES of Cohen’s d can be distinguished according to Hopkins et al. [27] (i.e., trivial (<0.2), small (0.2–0.6), moderate (0.6–1.2), and large (1.2–2.0)). Sufficient concurrent validity was presented by trivial ES (ES < 0.2) and a large correlation (r ≥ 0.90). Data were analyzed using IBM SPSS Statistics version 27.0 (IBM Corp., Armonk, NY, USA). Statistical significance was set at p < 0.05 (two-tailed).

3. Results

A total of 23 participants completed the study, but the metabolic data of one participant were lost due to equipment failure. Therefore, these data points were excluded from the corresponding analyses.

3.1. Comparison between Skip-30 s and Skip-3 min

Table 2. Comparison between Skip-30 s and Skip-3 min.

	Skip-30 s (I)	Skip-3 min (J)	95% Confidence Interval (I)–(J)		|d|	p-Value
Skipping Performance (n = 23)
Total count of loops by IJRU	82.91 (28.88)	445.00 (141.02)	−411.52,	−312.65	3.17	<0.01
Skipping rate (skips·min−1)	165.83 (57.77)	148.33 (47.01)	8.36,	26.62	0.83	<0.01
Metabolic Responses * (n = 22)
MET	4.79 (1.01)	8.00 (1.26)	−3.63,	−2.78	3.27	<0.01
Peak $\stackrel{·}{\mathrm{V}}$O2 (mL·min−1·kg−1)	29.20 (6.41)	41.99 (8.68)	−16.36,	−9.23	1.55	<0.01
Average $\stackrel{·}{\mathrm{V}}$O2 (mL·min−1·kg−1)	16.76 (3.53)	27.98 (4.42)	−12.71,	−9.74	3.44	<0.01
Average HR (beats·min−1)	148.88 (24.66)	166.29 (14.86)	−25.10,	−9.71	1.00	<0.01
% of $\stackrel{·}{\mathrm{V}}$O2max (%)	59.28 (14.45)	84.86 (20.38)	−34.18,	−16.97	1.32	<0.01
Perceptual Responses (n = 23)
Post-exercise RPE	11.53 (2.29)	14.26 (2.28)	−3.47,	−2.36	2.28	<0.01
Shoulder MS	2.17 (0.94)	3.17 (0.89)	−1.43,	−0.57	1.00	<0.01
Chest MS	1.96 (0.82)	2.61 (0.94)	−1.01,	−0.29	0.78	<0.01
Groin MS	1.78 (0.74)	2.52 (0.85)	−1.06,	−0.41	0.98	<0.01
Quadricep MS	2.26 (1.05)	3.39 (1.16)	−1.51,	−0.75	1.30	<0.01
Upper Back MS	1.91 (0.79)	2.70 (1.06)	−1.13,	−0.44	0.98	<0.01
Lower Back MS	2.04 (0.88)	2.48 (0.95)	−0.72,	−0.15	0.66	<0.01
Gluteus MS	2.35 (1.11)	3.04 (1.07)	−1.03,	−0.36	0.91	<0.01
Hamstring MS	2.26 (1.14)	3.39 (1.07)	−1.46,	−0.80	1.49	<0.01
Calf MS	3.00 (1.31)	4.09 (0.90)	−1.48,	−0.70	1.21	<0.01
Overall MS in Upper Body #	7.96 (3.05)	10.78 (3.05)	−4.03,	−1.63	1.02	<0.01
Overall MS in Lower Body ^	11.49 (4.62)	16.13 (3.90)	−5.86,	−3.45	1.67	<0.01

Note: Means (standard deviations) are presented unless specified otherwise. * Data lost due to equipment failure (n = 22). # Total score = 25; ^ Total score = 20. Abbreviations: IJRU, International Jump Rope Union; MET, metabolic equivalent of task; HR, heart rate; $\stackrel{·}{\mathrm{V}}$O₂, oxygen consumption; $\stackrel{·}{\mathrm{V}}$O_2max, maximum oxygen consumption; RPE, rate of perceived exertion; MS, muscle soreness.

summarizes the skipping performances, metabolic responses, and perceptual demands resulting from the two skipping protocols. Of the available paired metabolic data, participants skipped faster in Skip-30 s, with a significant difference (p < 0.01, d = 0.83). However, their $\stackrel{·}{\mathrm{V}}$O₂ and HR responses during Skip-30 s were significantly lower than those during Skip-3 min, with large effect sizes (p < 0.01, d = 1.55 and p < 0.01, d = 1.00, respectively). Figure 3 illustrates the changes in the $\stackrel{·}{\mathrm{V}}$O₂ and RER, taking the values of every five seconds of breath-by-breath data.

In terms of perceptual demands, Skip-30 s was less demanding than Skip-3 min, with participants rating the perceived exertion during Skip-30 s as somewhat hard (11.53 ± 2.29) and the perceived exertion during Skip-3 min as hard (14.26 ± 2.28), with a statistically significant difference (p < 0.01, d = 2.28). Participants also reported greater overall muscle soreness in their upper and lower body (p < 0.01, d = 1.02–1.67) after Skip-3 min than after Skip-30 s. Specifically, participants reported significantly more soreness after Skip-3 min than after Skip-30 s in all muscle groups, with from moderate to large ESs (p < 0.01, d = 0.66–1.49).

3.2. Concurrent Validity

The concurrent validity was assessed by examining the agreement between the E-rope and a certified IJRU judge in counting the number of skips completed by participants in Skip-30 s and Skip-3 min. All 23 participants completed both skipping protocols in both visits. The Pearson’s correlation coefficients between the E-rope counts and judge’s count were high for both the Skip-30 s (r = 0.99, p < 0.01) and Skip-3 min (r = 0.99, p < 0.01), indicating strong agreement between the two measures. The E-rope counts were moderately higher than those of the judge in both Skip-30 s (mean difference: 3.72 ± 4.92, (95% CI: 2.26, 5.18), p < 0.01, d = 0.76) and Skip-3 min (mean difference: 11.74 ± 15.22, (95% CI: 7.22, 16.26), p < 0.01, d = 0.77).

3.3. Between-Day Test–Retest Reliability

From good to excellent test–retest reliability was found for both measures. Between the two testing sessions, the ICC_3,1 values of the counts by the judge were high for both the Skip-30 s (0.87, 95% CI: 0.72–0.95) and Skip-3 min (0.94, 95% CI: 0.86–0.97) exercises, indicating good consistency in the measurements across the two testing sessions. The E-rope counts also had high ICC_3,1 values for both the Skip-30 s (0.89, 95% CI: 0.77–0.95) and Skip-3 min (0.95, 95% CI: 0.88–0.98) exercises. The CVs showed that the E-rope had similar relative variability in the combined scores from the two measures (3.68–5.70%) compared to the counting by the judge (4.72–7.52%). The SEM and MDC were also calculated separately for Skip-30 s and Skip-3 min for both measures. The SEM values for Skip-30 s were from 9.08 for the E-rope to 10.43 for the judge, and the MDC values were from 25.16 for the E-rope to 28.91 for the judge. The SEM values for Skip-3 min were from 27.87 for the E-rope to 32.94 for the judge, and the MDC values were from 77.26 for the E-rope to 91.31 for the judge.

4. Discussion

This study was the first to compare the metabolic and perceptual responses of apparently healthy young participants to two all-out rope-skipping events, Skip-30 s versus Skip-3 min, and to examine the accuracy of the self-counting function of the adopted E-rope. Our findings showed that Skip-3 min demanded significantly more metabolic and perceptual demands than Skip-30 s, as evidenced by the higher $\stackrel{·}{\mathrm{V}}$O₂, average HR during exercise, RPE, and muscle soreness scores at all marked muscle regions. The changes in the $\stackrel{·}{\mathrm{V}}$O₂, RER, and HR during both events indicated the dominance of anaerobic metabolism. Our study also found that the E-rope demonstrated from good to excellent reliability as a self-counting tool in both Skip-30 s and Skip-3 min. However, it tended to overestimate the number of skips, with a moderate effect size.

The rope-skipping exercises in the present study induced dissimilar responses in the body, compared with earlier study findings on rope skipping and conventional aerobic modalities. Skip-30 s and Skip-3 min were averagely equivalent to 4.79 ± 1.01 and 8.00 ± 1.26 METs, respectively; consequently, both events can be defined as MVPA (i.e., ≥3.00 METs) [13,14]. Collectively, all-out rope skipping can be considered a high-intensity exercise, and it is a mode of exercise that can be easily performed in a self-initiated manner. This simplicity makes it accessible to most individuals and it can be an effective way to achieve high-intensity exercise. However, our study found that when skipping all-out, participants only achieved a submaximal intensity. Therefore, it is unlikely that the training benefits of high-intensity sprinting or cycling could be fully replaced by rope skipping due to the diverse metabolisms elicited by different modes of exercise [28]. In terms of motor competence, previous studies have shown that incorporating submaximal rope skipping (120 skips·min⁻¹) into warm-up routines can improve young soccer players’ balance and motor coordination [6]. A five-minute-interval rope-jumping program (100–140 skips·min⁻¹ with a work–rest ratio of 30s:30s) has also been shown to be effective in improving endurance runners’ jump performance and 3 km running results, and in reducing foot-arch stiffness [8]. Therefore, all-out skipping-specific protocols may have varied benefits for different populations and should be further investigated.

Our findings showed that for different exercise durations, a short bout at a higher skipping rate (i.e., Skip-30 s) required less metabolic demands compared to a long bout at a lower skipping rate (i.e., Skip-3 min). This finding contrasts with a previous study [17] that standardized the exercise duration to 5 min at a submaximal intensity and found that a faster skipping rate resulted in higher $\stackrel{·}{\mathrm{V}}$O₂. The disparities in findings may be due to differences in the emphasis on the exercise intensity or duration in the respective exercise program. Moreover, the longer exercise duration in Skip-3 min led to a higher peak $\stackrel{·}{\mathrm{V}}$O₂, which occurred after the cessation of Skip-30 s. This may be related to the short duration of Skip-30 s, during which the $\stackrel{·}{\mathrm{V}}$O₂ did not have adequate time to reach its peak because of the rest-to-exercise transition. When brief exercise abruptly starts from a resting state, $\stackrel{·}{\mathrm{V}}$O₂ rises exponentially over time but does not have enough time to stabilize, and so the peak $\stackrel{·}{\mathrm{V}}$O₂ may only be attained after the end of exercise [29].

Another important finding of our study is that the exercise duration in an all-out manner did not affect the reliance on glycolysis and oxidation pathways in the early phase of exercise (i.e., 30 s). Our results showed that the major energy supply during this period relied heavily on muscle phosphagens and glycogen, as indicated by the RER peaking at 1.07 and 1.15 for all-out Skip-30 s and Skip-3 min, respectively, within the first 10 s after the onset of exercise. This suggests that the participants had already achieved or were close to their maximal rate of output at this time point. Subsequently, the RERs gradually decreased over the next 30 s, indicating a shift from a carbohydrate-dominant to a fat–carbohydrate combination as the energy source. However, as the Skip-3 min continued, its RER gradually increased to a higher ratio (>1.0) until the cessation of exercise, indicating a heavier reliance on glycolysis and oxidation pathways. The contribution of aerobic metabolism during Skip-3 min (84.86% of $\stackrel{·}{\mathrm{V}}$O_2max) was similar to that observed during high-intensity cycling (ranging from 72% to 85% of $\stackrel{·}{\mathrm{V}}$O_2max) [30]. Exercise intensity at about 70% of $\stackrel{·}{\mathrm{V}}$O_2max was discovered to reflect the switch of the principal metabolic demand from aerobic to anaerobic [31], indicating that Skip-3 min required a substantial anaerobic energy supply.

Apart from the metabolic responses, our study revealed a lesser level of perceived exertion and muscle soreness when a shorter all-out skipping bout was applied. This finding is consistent with a recent study on HIIT, which found that shorter HIIT bouts are perceived as less effortful than longer intervals, even when the overall workload is the same [20]. Additionally, the distribution of muscle soreness may also affect the extent of exercise exertion. In rope skipping, localized muscle soreness is likely due to metabolic acidosis during exercise [32], which seems to be more pronounced in the lower limbs, especially the calves. There are several possible explanations for these findings. Firstly, maintaining postural stability during exercise requires the activation of major muscle groups throughout the body. Skippers with higher skill levels tend to adopt a more kyphotic posture during speed events, which may reduce the jump height and flight time and allow for faster skips [33]. Although the lower extremities play a major role in rope skipping, skippers also need to coordinate and stabilize different body regions for effective skips. Consequently, it is important to consider the overall muscle involvement in rope-skipping events. Secondly, participants with limited rope-skipping experience may have higher average ground contact impacts, leading to increased muscle soreness scores. Studies have shown that adults performing bilateral jumping exercises can produce ground impacts of 2.87–5.39 times their body weight, depending on their relative jump height [34]. However, experienced skippers can limit these impacts to three times their body weight or less [35]. As a result, eccentric muscle contraction of the calf might be increased to cushion these impacts, leading to localized muscle soreness in the calf. Future studies could incorporate a force platform to investigate this issue further.

An additional important finding of our study is that the E-rope demonstrated high levels of concurrent validity and between-day reliability, indicating that it is a reliable and valid tool for measuring rope-skipping performance. The accuracy of the E-rope was highly correlated with the counting of an IJRU judge, and the MDC was calculated for the E-rope, allowing users to determine meaningful changes beyond measurement error. It is noteworthy that the E-rope moderately overestimated the actual number of skips counted by the judge. This may be due to the E-rope assuming that a successful skip is completed when the rope finishes a loop at the bearing of the main handle. Therefore, the rope may have completed a loop just before the participant tripped over it, resulting in overestimation. However, the E-rope is still considered a useful tool for remotely monitoring and encouraging rope-skipping training, particularly when traveling. With interactive mobile technology and knowledge of the metabolic responses during rope skipping, coaches and teachers can remotely advise skippers’ performance and prescribe exercise programs.

While the study provides valuable insights into the metabolic and perceptual responses to rope skipping and the accuracy of the self-counting function of the E-rope, there were several limitations that should be addressed. The within-subject design with repeated measures, convenience sampling, and limited sample size may have introduced bias and limited the generalizability of the findings. Additionally, the study did not investigate the effects of the rope-skipping skill levels or jump-skipping efficiency, which could be important factors to consider in future research. To improve the validity and generalizability of future studies, it may be useful to incorporate electromyography to analyze the effects of different postures and skill levels of rope skippers. Furthermore, future studies should aim to recruit a more diverse sample with a larger sample size that includes individuals of varying ages and levels of rope-skipping experience to expand the understanding of the efficacy and validity of the E-rope.

5. Conclusions

In conclusion, skipping exercises of both shorter (30 s) and longer (3 min) durations were considered moderate–vigorous-intensity exercises (≥3.0 METs), with the longer bouts requiring more energy expenditure and resulting in greater perceived exertion and post-exercise muscle soreness. Both durations predominantly utilized carbohydrates as fuel. The E-rope used in the study was a reliable and valid self-monitoring tool for coaches and athletes, despite slightly overestimating the number of skips. Overall, the results suggested that the exercise duration of all-out skipping should be adjusted based on the training purpose, with a shorter duration being recommended for enhancing the stretch–shortening cycle due to the accompanying higher skipping rate, while a longer duration is suggested for building cardiorespiratory fitness. The adoption of the E-rope, along with other sharing and monitoring technologies, allows sports coaches and strength and conditioning coaches to prescribe athletes a wider variety of training programs using a minimal amount of equipment and space, even when they are not present.