DOI: https://doi.org/10.21203/rs.3.rs-2102064/v1
Background: The aim of this study was to analyse the effects of low-volume CT performed during 6 weeks on muscle power, muscular strength, maximal aerobic power (Wmax) and internal load in active young adults.
Methods: Eighteen healthy, active young adults men (mean ± SD, 20.06 ± 1.66 years; 22.23 ± 2.76 kg-1m2) performed either a low-volume CT (GE, n=9), or maintained a normal life (CG, n=9). The CT was composed of a resistance training (RT, 2 sets of 3 exercises with 80 to 85% 1RM) followed by a high intensity-interval training (HIIT, 5 sets of 60’’ with 95% Wmax). The measures of jump height, 1 maximal repetition (1RM) in bench press and back squat, Wmax and internal load were obtained before (pre) and after (post) training to analysis. Furthermore, an ANOVA test of repeated measures and t-test paired samples were used with a p ≤ 0.05.
Results: Low-volume CT increased from pre to post on jump height (29.28 ± 3.81 to 32.02 ± 3.09cm, p ≤ 0.05), 1RM on bench press back squat (56.11 ± 11.35 to 67.67 ± 13.36kg, p < 0.001 and 63.11 ± 12.25 to 74.00 ± 12.02kg, p < 0.001, respectively) and Wmax (200 ± 30 to 220 ± 30.92W, p ≤ 0.01). The internal load had not significant differences between weeks (p > 0.05).
Conclusions: In healthy, active young adults men the low-volume CT is effective to improve, jump height, 1RM in bench press and back squat, and Wmax without increase internal load.
In sports there are various modalities that benefit from the simultaneous development of aerobic (i.e, cardiorespiratory fitness [CRF]) and anaerobic capacities (i.e, strength, and power) to increase the sports performance [1–3]. The combined training (CT) is defined by the realization in the same session of resistance training (RT) plus aerobic training (AT). Furthermore, CT plays an important role for the development of many components of physical fitness (PF) associated to sports performance in simultaneous and are used to several coaches [4–7]. CT can also increase muscular strength [4–7], muscle hypertrophy [4, 7], CRF [3–5], anaerobic capacity [4] and muscle power [3, 4, 7]. Despite these advantages for PF, the training sessions can be very long (i.e., > 60 min) which can be considered a limitation of this strategy [8, 9]. However, it allows a reduction in total time spent on performing RT and AT in separate ways [10], without affecting chronic adaptations to training [5, 7].
AT as low-volume high-intensity interval training (HIIT) is characterized by training protocols which the weekly volume is under than ACSM guidelines, ≥ 500 metabolic equivalent - MET/min/week [11]. These protocols seem to be able to increase the CRF, however, they are not enough to obtain changes in body composition [12], but are also promising strategies for improving performance in athletes [13]. For RT, the low-volume is defined by single sets, low repetitions and high load [14] with a low weekly frequency [14], a strategy able to improve muscular strength in untrained individuals [11, 14, 15] and in trained when the training frequency is twice or three times a week [15]. The low-volume RT has yet the capacity to increase muscle power and function [15].
So, the benefits for sports performance of CT are already known, as well the efficacy of the low-volume exercise to improve some components of PF. However, there isn’t scientific evidence which analyse all these variables inserted only in a single exercise protocol, to reduce weekly and daily total time spent in exercise and have de same benefits of both training methodologies. Therefore, the aim of this study was to analyse the effects of 6 weeks of low-volume CT on muscle power, muscular strength, and maximal aerobic power (Wmax) in healthy active young adult men.
In this research it was hypothesized that low-volume CT could significantly increase muscle power, muscular strength, and aerobic power, in healthy active young adult men. Using a non-randomized, between groups design (experimental group [EG] and control group [CG], respectively), 18 young adults were evaluated. To investigate the potential effects of CT on power, strength and Wmax measures of squat jump height, 1 maximal repetition (1RM) on bench press and back squat and maximal Watts (W) on graded incremental test on cycle ergometer were performed before and after a 6 weeks intervention period. All subjects performed familiarization trials before the testing days and one familiarization training session prior to intervention period.
Eighteen healthy active young males, students of sports degree were recruited to participated in this study. The subjects were not involved in any training routine, either RT or AT or both, for at least 6 months, but were involved in practical activities associated with the undergraduate study plan such as football, handball, and fitness activities up to 4 hours per week. During the experimental period, participants were not involved in any more recreational activities or any type of physical exercise. All subjects underwent pre-exercise screening to ensure they had no established cardiovascular, metabolic, or respiratory disease nor signs or symptoms of disease, musculoskeletal injuries, health problems or required medication. The use of any type of supplementation or ergogenic substance was not permitted and, subjects were instructed not to change their diet or lifestyle over the experimental period. The physical characteristics of each group are shown in Table 1. All subjects signed a written informed consent and voluntarily agreed to participate in this study, and all procedures were approved by the Polytechnic Institute of Beja ethics committee (CEIPBeja).
| Variables | EG (n = 9) | CG (n = 9) | |||
|---|---|---|---|---|---|
| Mean | SD | Mean | SD | p | |
| Age (years) | 20.56 | 1.67 | 19.56 | 1.59 | 0.21 |
| Body weight (kg) | 69.51 | 10.59 | 70.36 | 10.67 | 0.87 |
| Height (m) | 1.76 | 0.07 | 1.79 | 0.08 | 0.39 |
| BMI (kg/m2) | 22.46 | 2.88 | 21.99 | 2.78 | 0.73 |
| Squat jump height (cm) | 29.28 | 3.81 | 30.82 | 4.35 | 0.44 |
| 1RM back squat (kg) | 63.11 | 12.23 | 65.89 | 12.66 | 0.64 |
| 1RM bench press (kg) | 56.11 | 11.35 | 52.33 | 15.99 | 0.57 |
| Wmax (watts) | 200 | 30 | 211.67 | 35.53 | .463 |
| Note: Data are presented in mean ± SD. BMI = Body mass index; 1RM = 1 maximal repetition; Wmax = maximal aerobic power. Statistically significant values (p ≤ 0.05) are presented with *. | |||||
The first physical contact with subjects was a familiarization trial followed by pre-test measures, later was done a familiarization training session. The followed weeks were the intervention period, culmination in post-test in the last week. Each pre and post tests were performed in laboratory with the supervision of the investigator as well as the same conditions pre and post tests were guaranteed. All subjects were asked to avoid vigorous and intense physical activities at least 48 hours before tests. An order of evaluation was established, equal to all subjects and evaluations: jump height, 1RM in the squat, 1RM in the bench press and to finish the evaluation of the Wmax in the cycle ergometer. The subjects were allocated in two groups, the CG (n = 9) that did not perform any experimental procedure and followed their daily routine and the EG (n = 9) who underwent a RT followed by a HIIT on the cycle ergometer, explained below. No dropouts were reported during the experimental period.
Anthropometry. Measurements were done using an stadiometer with an accuracy of 1 cm (Seca mod. 213), the subjects were measured shoeless. Body weight was measured from a calibrated scale with an accuracy of 0.1kg (SC-330, Tanita corp, Tokyo, Japan).
Squat Jump Height. It was measured employing the squat jump test, based on kinematic equations that use the flight time measured using Optojump (Microgate Co., Bolzano, Italy), in accordance with the protocol [16]. Before starting the test, a warm-up of 5 minutes was performed with low intensity body weight exercises and a pre-test submaximal jump. The subjects started from the upright standing position with their hands on their hips, they were then instructed to flex their knees and hold a predetermined knee position (approximately 90), and the experimenter then counted out for 3 seconds. On the count of 3, the subject was instructed to jump as high as possible without performing any countermovement before the execution of the jump. Was recommended that at takeoff the subjects leave the floor with the knees and ankles fully extended. Three jumps were made with two minutes rest between each try and only the highest value was analysed [16].
1 Repetition-Maximal. The 1RM was analysed in horizontal bench press and back squat, all of them were made with an olympic bar with 20kg and in a free hack. A linear velocity transducer (T-Force System Version 3.60, Ergotech, Murcia, Spain) was used to predict 1RM in each exercise [17]. This equipment automatically calculates the kinematics of each repetition performed and provides %1RM, the mean propulsive velocity and both are used for the calculation of the 1RM by software [18]. Only loads above 60% of 1RM were used for pre-evaluation, to increase the reliability of the measurement and in the post, evaluation was used the same load established in the post-evaluation [17, 19]. General warm-up consisted of performing 5 minutes of exercises with low intensity (i.e., jumping jacks and split jacks), 2 sets of 20 repetitions each, followed by a gentle stretching and joint mobilization, the specific warm-up were 2 sets of 5 repetitions with 30 and 20 kg for bench press and back squat, respectively. Subsequently, 1 set of 3 repetitions was performed, where the load was progressively increased with small and individual increments (i.e., 2.5 to 10kg) until the relative load was over than 60% of 1RM. The intervals periods between sets were 3 to 5 minutes. Unlike the eccentric phase, which was performed at a controlled mean bar velocity (~ 0.50 to 0.70 m s − 1) for standardization and security reasons, participants were verbally and strongly encouraged to perform the concentric action in an explosive manner, at maximal intended velocity. Only concentric phase and the repetitions that match with a full range of motion and technique were analysed, like touch on chest in bench press and 60º of knee flexion in sagittal plan back squat. In bench press subjects were not allowed to bounce the bar off their chests so as not to boost the bar velocity [20]. The exercises technique was described in [19], except for back squat that was performed only until 55º and 65º of tibiofemoral flexion in sagittal plan. The range was guaranteed by a seat placed behind the subject, and they were encouraged to only touch and did not sit down.
Maximal Aerobic Power. Wmax, was measured by a maximal graded exercise test on cycle ergometer (GXT CE) with mechanical calibration (Ergomedic 828E, Monark, Sweden), under the supervision of the investigator and in accordance with the protocol of Storer et al. [21]. The warm-up consisted of 2 minutes with a 60 W of load with a pedal rate of 60 repetitions per minute (RPM), after that the intensity was increased by 15 W every minute. The test was interrupted when it was no longer possible to maintain 60 RPM or until the subjects reach their limit of tolerance. The protocol was adapted in the warm-up, to not cause loo long tests and avoid prediction errors [22]. Subjects were verbally encouraged before and during the test administrators to provide a true maximal effort. Wmax was recorded in the final stage only when this stage was fully completed.
Volume Load. The volume load (VL) was calculated in all sessions using the following formula: (number of series × number of repetitions × external load in kg). To calculate the total weekly VL, the total volume of all exercises in that same week was added. Only repetitions performed with a full range of motion and with a proper technique were included on the analysis. The values are expressed in kilograms (kg) [23].
Internal Load. The Category ratio-10 scale (CR-10 RPE) of rating perceived exertion (RPE) was used to measure the exercise intensity[24]. The internal load was calculated by multiplying the RPE by the total session time in minutes (RPE × total session time in min) [23]. For the calculation of the weekly internal load, the internal load of the sessions in this week was added, the values are displayed in arbitrary units (a.u). To avoid measurement errors, before starting an explanation of the tool consisted of and a familiarization with the scale was performed. The subjects were asked to evaluate the total effort of the session. The values were recorded after 15 minutes from the end of session [23].
Combined Training Protocol. The CT was realized twice a week with 48 hours of interval between each training session for 6 weeks in a row, with a physical exercise technician always supervising the training sessions. General warm-up was the same used to 1RM tests. The specific warm-up was 1 submaximal set of 6 repetitions with 60% of 1RM to enhance the force production and power during the work sets [25]. The CT consisted in a session of RT before a HIIT on cycle ergometer (i.e., Monark 828E). For the RT, 2 sets of three multi-joint exercises, squat with a hexagonal bar, flat bench press with bar and 30º incline bench pull with bar, always with this order, were performed. A recovery time of 2 minutes between sets and exercises was strictly controlled. The subjects were instructed to perform the repetition movement velocity (i.e., Tempo) in 3 to 4 seconds for eccentric phase and a maximal intended velocity in the concentric phase. All exercises and sets were performed of an intensity between 80 to 85% of 1RM (6 to 8 RM) during all intervention. The subjects were instructed to perform all sets to concentric failure or close to. The load progression was made according to the 2-by-2 rule (2 to 5% for upper limbs and 5 to 10% for lower limbs) [26]. The loads used and repetitions performed of all participants were recorded for the calculation of the VL. After 3 minutes of passive rest, the HIIT started, on a cycle ergometer. The warm-up consisted in 2 minutes with 15 to 45 W at 60 RPM. Then, 5 sets of 60 seconds at 80 to 90RPM with 95% Wmax with 90 seconds of active pause at 50–60 RPM with a self-suggested load up to 60W were performed. The work:rest ratio was 1:1.5 and in the end the calm down was 2 to 3 minutes at 50 to 60 RPM with a self-suggested load. No injuries or dropouts were reported, and the training adherence was 100%.
The normality and homogeneity (Shapiro–Wilk e Levene test, respectively) were conducted in all data before analyses. All data were presented in mean ± SD and was adopted 95% confidence intervals. For the comparison between groups, an independent samples T-test was used. An ANOVA of repeated measures was used to analyse the effects time, groups and the interaction time-group of jump height, 1RM bench press, 1RM squat, Wmax, VL and internal load. The paired-samples T-test was used to compare the means between groups in the pre and post measures. The alpha criterion for significance was set at p ≤ 0.05. All data processing was performed in the Statistical Package for Social Sciences (IBM SPSS Statistics for Windows, Version 27.0, IBM Corp., Armonk, NY, USA).
There was not a significance differences for baseline measures between groups in analysed variables (p > 0.05).
A significant group × time interaction was observed for jump height (Z1,16 = 5.703, p = 0.030), only in EG (pre: 29.28 ± 3.81 cm vs. post: 32.02 ± 3.09 cm, p ≤ 0.05) (Fig. 1).
A significant group × time interaction was observed for 1RM in bench press (Z1,16 = 14.214, p = 0.002), only in EG (pre: 56.11 ± 11.35 kg vs. post: 67.67 ± 13.36 kg, p < 0.001) (Fig. 2).
A significant group × time interaction was observed for 1RM in back squat (Z1,16 = 22.149, p < 0.001), only in EG (pre: 63.11 ± 12.25 kg vs. post: 74.00 ± 12.02 kg, p < 0.001) (Fig. 3).
A significant group × time interaction was observed for Wmax (Z1,16 = 14.286, p = 0.002), only in EG (pre: 200.00 ± 30.00 W vs. post: 220.00 ± 30.92 W, p ≤ 0.01) (Fig. 4).
There was a significant main effect of time in VL (Z4, 40 = 14.446, p < 0.001) (Fig. 5).
No changes in internal load occurred during the intervention between weeks (Z5,40 = 1.764, p = 0.143).
The purpose of this study was to examine the effects of 6 weeks of low-volume CT on muscle power, muscular strength, and Wmax in healthy active young adult men. The main results showed that all components of PF analysed, muscle power, muscular strength and maximal aerobic capacity improved significantly through low-volume CT. The VL had a significant and progressive tendency to increase between weeks, and without differences on internal load.
The neuromuscular component that seems to be most attenuated by CT is the muscle power or rapid/explosive force, due to a phenomenon called "interference effect", which affects chronic adaptations in power [7, 27–29]. Despite the greater interference effect, due to the possible limitation of neural activation speed [29], the CT can significantly increase the muscle power [7, 27–29]. However, [4] did not report any harmful effect at the jump height between the group that performed the CT in relation to what did only RT. A study [30] that assessed the jump height by the squat jump test also found a significant improvement of 6.6% after 12 weeks of CT, nevertheless the AT and RT were performed on alternate days, a strategy used to minimize the effect of interference between aerobic and neuromuscular adaptations [6, 7]. This study also found significant improvements of 9.4% in jump height. These results suggests that for young active adults low-volume CT may be enough to increase vertical jumping capacity, which is related to the anaerobic potency of lower limbs [31]. This chronic adaptation can be explained by improving the voluntary neural activation speed, related to the motor neuron recruitment speed and maximal motor unit discharge rate [32].
For muscular strength, it is already well documented in the literature, that CT increases maximal strength in the upper limbs and the lower limbs [5–7], which agree with the results obtained in this study either for 1RM in the bench press or for 1RM in the squat. In this study, the RT was done before than HIIT which it is the order that had better results to increase 1RM [5, 6]. A study of Winett et al. [33] found that even low-volume CT was able to improve strength in various exercises in untrained subjects. Another article methodologically similar to our study, which prescribed a higher daily volume for both of RT and AT, they found improvements in strength in the half squat [34]. The low weekly volume presented in this study appears to be effective to create neuromuscular adaptations and this result is supported by other articles that through prescription of single set with low weekly volume of RT were sufficient to increase maximal strength [15, 35]. This improvement can be explained by adaptations, especially neural, in relation to structural adaptations, due to the duration of the intervention period [36]. Some of these adaptions could be related to the increase of motor unit firing frequency and synchronization, motor unit recruitment thresholds, motoneurons excitability and an improvement in antagonist muscle coactivation [36]. Another interesting detail was the magnitude of the improvements in the present study (20.59% for bench press and 17.25% for squat) compared to other CT studies, which was an average of 16.55% increase in bench press [28, 37], and 23.6% in squat [38–40]. A possible interpretation of these results is that for upper limbs strength the low-volume CT can be as effective to increase strength as higher volume CT, however for the lower limbs the higher volume seems to be more effective for active individuals and untrained in RT. Despite this, more studies are required to be able to successfully compare the effects of CT of different volumes on muscle strength.
The CRF seems to be the component of PF with more positive responses to CT, due to a small or inexistent interference effect between training bouts, independently of exercise order [5, 6]. The Wmax is the maximum capacity to generate energy through the aerobic metabolism [41]. Improvements in Wmax are supported by this information and the positive association between CRF and Wmax [42]. This could be explained, particularly for untrained subjects, due to an increase in myofibrillar and mitochondrial protein synthesis, as well as mitochondrial biogenesis after CT [43]. An investigation led by Lee et al. [44], found that after 9 weeks of CT training with a higher weekly volume, moderately active young adults increased 7.1% of Wmax. The increase of 8.8% in Wmax was also obtained by Fyfe et al. [28] as a result of an 8 weeks of CT with a higher volume training protocol performed by active subjects. Another study with a duration of 12 weeks of CT conducted by Shamim et al. [30] in young active adults, resulted in a 14% increase in Wmax. The results reported in these studies are relevant when compared with our outcomes, because we had an increase of 10% in Wmax with a lower weekly training volume than the above-mentioned studies. This suggests that a smaller training volume may be as effective as to increase aerobic capacity in young active adults.
When measuring CRF through VO2max, there is more evidence pointing in the same way. A work of Winett et al. [33] who performed a low-volume CT protocol achieved significant improvements in VO2max in untrained subjects during 12 weeks of training. When addressing CT with a higher volume there is a wide literature that indicated to significant improvements of VO2max [38, 45–47].
For the measures of training load, the progressive increase in weekly VL between weeks was supported due to the application of the principle of progressive overload applied in the training sessions, which was the 2-by-2 rule [26]. This increments in VL could be associated to strength improvements in untrained men [48], this relationship may explain the increase in muscle strength, due to the increase in VL in the 6th week. Despite this increase in VL, the internal load did not increase and still presented a decreasing trend, which was not the case in the study of [28], which had some fluctuations in the internal load. That could be explain by the study design because the change the intensity zone of RM between the weeks of intervention, as well as its multifactorial response [49]. The internal load is a psychophysiological indicator where the effort of the entire training session is measured in a relative way [23] and a higher internal training load can increase vulnerability for diseases or injuries [50]. This situation gives us information that there was less effort and less perceived physiological stress while training and therefore is expected a less possibility to have an injurie or disease.
This investigation has some limitations which should be considered before drawing conclusions. The group sample is small and that can affect the statistical power and by being associated with a group of students of the sports degree who already practiced physical activity before and during the experimental period. Nevertheless, there was a CG that had the same characteristics of the EG, but they did not perform the training. The training protocol duration was only 6 weeks, although it was already possible to see significant differences in PF. Food, alcohol intake or tobacco intake were not controlled, although subjects were asked to keep their usual routines. The training sessions were not always given on the same days or at the same time, but the researchers always tried to ensure an interval of 48h between workouts to ensure a good recovery. Finally, all the results obtained can only be considered for the research population and should not draw conclusions for populations with other characteristics.
In future investigations it will be necessary to use a more representative sample and with another type of population so that we can draw more conclusions. Perhaps, in individuals with training experience to check if even with lower volumes of training can be achieved improvements. It may be interesting to use morphological evaluations to examine the musculoskeletal hypertrophic response to low-volume CT. Could be interesting to create an extra group that performs even less volume to draw more conclusions about the minimal dose of exercise. Longer investigations may lead to more significant results. However, this remains hypothetical and requires further investigation to elucidate these topics.
The CT was effective to increase the muscle power of lower limbs, maximal muscular strength in bench press and back squat and the maximal aerobic capacity without increase the weekly internal load and with less time spent in exercise than traditional recommendations. The low-volume CT can be used as a resource to increase PF and consequently sports performance in various recreational sports, without increasing the chance of a state of overtraining, however more studies are needed to confirm these results. From a practical approach, this is helpful information for coaches who work with healthy young adults, due to the efficacy of this training program to improve PF measures in 6 weeks of low-volume CT.
The authors declare that were supported by others certified professionals for supervised the workouts and evaluation process during the experimental period.
The authors have no conflicts of interest to disclose.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
The study was performed following the Declaration of Helsinki and was approved by the ethics committee of Polytechnic institute of Beja (CEIPBeja).
The participants were volunteers, without a monetary incentive and were informed about the use of their information. Informed consent from each participant was obtained.