The Effect of Concurrent Resistance Training on Tethered Force, Lower Limbs Strength, Anaerobic Critical Velocity, and Swimming Performance: A Randomized Controlled Trial

Abstract

Background: Combining pool-based and resistance workouts, both in the pool and on dry land, is a valuable approach to enhancing swimming performance. However, few investigations have been conducted on this topic. Through a randomized controlled trial study, we investigated the effects of a 10-week concurrent resistance training program, which integrated resistance workouts both in the pool and on dry land on tethered force, lower limbs strength, anaerobic critical velocity, and swimming performance, in regional age-group breaststroke swimmers. Methods: Regional age-group swimmers (N = 24, males) were randomly divided into two groups. The experimental group (EG: 15.1 ± 0.5 years old) performed combined pool-based + resistance workouts, both in the pool and on dry land. The control group (CG: 15.1 ± 0.7 years old) performed their usual training regime, i.e., pool-based + resistance workouts on dry land only. The tethered swimming force, muscular strength, anaerobic critical velocity, and swimming performance and technique of the swimmers were evaluated before the training program began and after 10 weeks. Results: Improvements were observed in the EG vs. the CG in terms of the mean force (30.04%, p = 0.02; d = 0.75), one-repetition maximum back squat (20.57%, p = 0.01; d = 2.05), maximal force (19.23%, p = 0.03; d = 0.69), and anaerobic critical velocity (4.2%, p = 0.04; d = 0.61). The 50 and 200 m breaststroke performance times improved (4.3 and 5.4%, p = 0.01, d = 0.88–0.92, respectively) after 10 weeks. Conclusions: With the increasing demands of contemporary swimming competitions, which often include heats, semifinals, and finals, achieving optimal physical fitness to compete at an elite level, in every round, is vital for swimmers. The combination of resistance training workouts both in the pool and on dry land seems to enhance swimming performance in age-group swimmers, particularly in sprint to middle-distance breaststroke swimmers.

1. Introduction

Research investigating the impact of dry-land strength and conditioning on swimming performance has been influenced by the specificity of the training methods [1] and training intensity [2,3]. The training approaches encompass three primary perspectives: dry-land strength training, specific in-water resistance training, and concurrent training [4]. Dry-land strength training refers to a conventional resistance training approach that employs a gym-based strength program and swim-like resistance exercises, utilizing a swim bench [5] to primarily enhance a swimmer’s strength and power [6,7]. Substantial in-water submaximal strength training is performed through in-water resistance training, incorporating leg-kicking exercises [8], resistance bands, hand paddles, or parachutes to counteract the increased resistance [9,10,11,12]. Concurrent training by competitive swimmers, combining a strength training program together with swimming training [4], has been shown to enhance physiological changes, both in terms of the swimmer’s aerobic and anaerobic capacity, their energy expenditure during locomotion, and their maximal power [13].

The dynamic process of training periodization is one of the most essential areas of training theory in sports. At the top of the hierarchical periodized system is multiyear preparation, followed by macrocycles, which are typically divided into three training periods over a season or year. The initial preparatory period involves high-volume training at low-to-moderate intensities, with varied exercises to build general physical fitness and technical skills. The second period emphasizes more sport-specific work, while the third, the competition period, includes race pace-specific exercises, with a reduced training volume [3]. In addition, it is well reported that strength and conditioning programs designed for young swimmers should include a wide variety of strength training practices in their periodized strength training program [4,14,15]. Traditionally, strength and conditioning plans that follow periodization emphasize the development of muscle endurance through the application of moderate external loads. This involves performing 2–3 sets of 6–8 repetitions, utilizing weights that constitute 50–75% of the individual’s one-repetition maximum (1-RM) [9,16]. Conversely, substantial loads are employed to increase the individual’s maximum strength. This includes executing 3–5 sets of 3–5 repetitions, with weights above 85% of the individual’s 1-RM, with a rest interval of 2–3 min between sets [9,17]. Moreover, to enhance speed strength and power, training with low-to-medium loads occurs, generally between 30 and 60% of the individual’s 1-RM [18].

Research on strength and conditioning training for young swimmers has primarily focused on front crawl technique [9,11,17,19] and butterfly [15], with little emphasis on lower limbs strength and power in breaststroke. Breaststroke is a technically tricky stroke, distinguished by intermittent propulsive phases, significant intracyclic velocity fluctuations, and a low average velocity [20]. Despite the technical limitations placed on swimmers in regard to breaststroke events, ranging from novices to elite competitors, there exists considerable scope for individual variation in terms of timing, coordination, neuromuscular activity, and pacing profiles [21].

From a biomechanical and physiological perspective, the breaststroke technique differs in terms of the extent to which the upper and lower limbs contribute to the propulsive forces. Increased power significantly enhances propulsive force, with the lower limbs playing a crucial role [20,22]. Consequently, coaches and trainers utilize strength and conditioning programs to enhance a swimmer’s kinematics, temporal patterns, and improve their neuromuscular performance. However, the benefits of combined strength training programs on breaststroke performance enhancement (from 50 to 200 m), and the findings, remain unclear in the literature. Thus, this study aimed to evaluate the effects of a 10-week concurrent resistance training program, incorporating resistance workouts both in the pool and on dry land on tethered force, lower limbs strength, anaerobic critical velocity (AnCV), and swimming performance, in regional age-group breaststroke swimmers. It was hypothesized that such an approach involving a combination of pool-based resistance workouts (using a parachute, fins, hand paddles, and specific kicking sets) with dry-land resistance workouts (which included back squats (BSs), reverse lateral lunges (RLLs), and dumbbell sumo–Romanian deadlifts (SRDLs)) would improve the swimmers’ tethered force, lower limbs strength, AnCV, and breaststroke swimming performance in events from 50 to 200 m.

2. Materials and Methods

2.1. Experimental Design

In this randomized controlled study, twenty-four male swimmers specializing in breaststroke were randomly assigned to either the experimental group (EG) or the control group (CG). The experimental group participated in a training program involving combined pool-based + resistance workouts, both in the pool (using a parachute, fins, hand paddles, and specific kicking sets) and on dry land (which included BSs, RLLs, and SRDLs). The control group performed their usual training regime, i.e., pool-based + resistance workouts on dry land only. We measured the swimmers’ breaststroke tethered swimming force (i.e., maximal force, mean force, fatigue index), maximum muscle strength (1-RM back squat), AnCV, swimming performance and technique (velocity, stroke rate (SR), stroke length (SL), and stroke index (SI)) for 50, 100, and 200 m breaststroke swimming. These measurements were taken before the training program began and after 10 weeks, for both the training conditions, during the first macrocycle of a traditional three-peak preparation program. Importantly, the swimmers were explicitly told not to engage in any additional physical training routine on velocity and power throughout the duration of the trial. Before the beginning of the training practices, all the participants were free from any injuries.

2.2. Participants

A sample size of 24 participants was considered sufficient (software G*Power, version 3.1.9.6), with an alpha level of 0.05, a power of 0.80, and an effect size of 0.5. Twenty-four breaststroke swimmers, competing at national and regional levels within their age categories, voluntarily participated in this study. The participants were assigned at random to participate in either the control group (CG, N = 12; age: 15.1 ± 0.7 years; height: 176.4 ± 1.8 cm; body mass: 67.4 ± 1.7 kg; 19.6 ± 0.27% of fat mass; competitive swimming experience: 3.8 ± 0.8 years; 560 ± 52 for 200 m breaststroke World Aquatics points) or the experimental group (EG, N = 12; age: 15.1 ± 0.5 years; height: 176.8 ± 2.0 cm; body mass: 65.8 ± 1.4 kg; 19.3 ± 0.4% of fat mass; competitive swimming experience: 4.0 ± 0.7 years; 578 ± 36 for 200 m breaststroke World Aquatics points). The inclusion criteria were as follows: (i) they had a minimum of 3 years of training experience; (ii) they participated in at least 90% of the training period; (iii) they were free from a current injury during the 10-week training period; and (iv) they did not participate in any other training program during the duration of the current study. The exclusion criteria were as follows: (i) a poor health status and physical condition, with potential medical problems, and (ii) incomplete participation in the training and testing program. The parents of the participants were informed about the benefits, risks of taking part, and the entire evaluative and experimental process involved in the current study, prior to signing an informed consent form, which was approved by the ethics board at the local university, code G-HS047/2567 (C1), and the study was performed according to the Declaration of Helsinki.

2.3. Procedures

2.3.1. Aquatic Resistance and Dry-Land Resistance Training

Pool-based training and swimming performance tests took place in a 50 m indoor pool, with 25–27 and 27.2–28.1 °C water and air temperatures, respectively, and 64–68% relative humidity during the data collection period. Dry-land training and strength tests were performed in a fitness training room. Aquatic resistance training, which included specific kicking sets, parachutes, fins, and hand paddles, was composed of two sessions per week. The water parachutes, fins, and hand paddles were used (2–3 sessions in a week) immediately after the warm-up (i.e., 500 to 800 m of aerobic training [i.e., 55% to 80% of maximum heart rate]) on Tuesdays and Thursdays. During the general phase (i.e., weeks 1–6), swimmers completed 3 sets × 6 repetitions × 15 m, with 60 s and 5 min of rest between repetitions and sets, respectively. During the specific phase (i.e., weeks 7–10), swimmers completed 2 sets × 4 repetitions × 25 m, with 60 s and 5 min of rest between repetitions and sets [23].

The specific kicking set was included in the training program for the EG only (2 sessions in a week), immediately after the warm-up (i.e., 500 to 800 m of aerobic training [55% to 80% of maximum heart rate]) on Wednesdays and Fridays. During the general phase (weeks 1–6), swimmers completed 3 sets × 6 repetitions × 50 m (i.e., 25 m kick, 25 m drills), with 60 s and 5 min of rest between repetitions and sets, respectively. During the specific phase (weeks 7–10), swimmers completed 2 sets × 5 repetitions × 50 m, with 90 s and 5 min of rest between repetitions and sets, respectively. The dry-land program was led by experienced strength and conditioning coaches, which included two sessions, weekly. Each session started with a 15 min standard warm-up, featuring dynamic stretching and functional, mobility, and aerobic exercises. Subsequently, the participants completed three lower body strength exercises, targeting lower leg strength, namely BSs, RLLs, and SRDLs, employing moderate contraction velocity and a full range of motion. The BS exercise was executed at an intensity ranging from 60 to 85% of the individual’s 1-RM. The sets ranged from 2 to 3 and the repetitions varied from 6 to 12 [23]. The SRDL was executed at an intensity ranging from 60 to 85% of the individual’s 1-RM. The sets ranged from 2 to 3, while the repetitions fluctuated between 6 and 10. The RLL comprised 6 to 8 sets of 6 to 12 repetitions. The resting period between sets and exercises was set at 2 min.

2.3.2. Testing Procedure

All the tests were performed within four consecutive days (standardized order): (i) before the start of pre-season training; on day one, anthropometric and body composition (i.e., height, body mass, fat mass) measurements were taken and all-out 200 m breaststroke swimming performance tests were conducted; (ii) on day two, the participant’s tethered swimming force was recorded, with their full breaststroke stroke/technique; (iii) on day three, the participants’ maximum muscle strength (1-RM back squat) was recorded and all-out 100 m breaststroke swimming performance tests were conducted; (iv) on day four, the participant’s AnCV was recorded (i.e., using performance times for a 10, 15, and 25 m swim) and all-out 50 m breaststroke swimming performance tests were carried out.

Anthropometry and body composition. The participant’s body mass and body fat (%) were assessed using bioelectrical impedance analysis (BIA), using a Body Composition Analyzer: Inbody270 (Inbody270, Yi Hui Medical Co., Ltd., Guangzhou, China).

Tethered force. A 30 s tethered swim test was conducted, according to the method described by Morouço et al. [24]. Briefly, each swimmer executed a maximum intensity breaststroke during all their effort. The measurement apparatus was a load cell system attached to the swimmer, capturing data at 100 Hz, with a capacity of 1.000 N. The maximal tethered swimming tests were conducted in a randomized order, using the complete breaststroke technique (i.e., upper and lower limbs movement). Continuous force data were collected for 30 s at 100 Hz and subjected to a 15 Hz cut-off digital filter (FIR, Blackman window, −61 dB). The cut-off value was determined using Fast Fourier transform to reduce artifact noise. The force variables, derived from individual force–time curves, were the maximum force, mean force, and fatigue index.

Muscular strength of the lower limbs. The maximum lower limbs strength was assessed using the 1-RM in terms of the BS (1-RM back squat). Swimmers performed a 3 min warm-up, followed by 5 min of comprehensive static stretching. Subsequently, each swimmer executed one set of eight repetitions at 50% and one set of three repetitions at 70% of their projected 1-RM back-squat. The load was progressively augmented (i.e., 10 to 20%), with 2 to 3 repetitions and with a rest period of 2 to 4 min implemented. Subsequently, a minor increment in the load (i.e., 5%) and the rest period of 2 to 4 min were implemented to achieve the 1-RM back squat. The test concluded when the subjects were unable to execute two repetitions of the BS, with the final successful attempt indicating the individual’s 1-RM back-squat.

Anaerobic critical velocity. Anaerobic performance was assessed using the method proposed by Fernandes et al. [25]. The AnCV was determined for each swimmer by utilizing the slope of the distance–time (Dd-t) relationship, plotting swimming performance times for 10, 15, and 25 m over time. The derived regression line equation is of the form y = ax + b, where “y” represents the distance swum, “x” denotes time, “a” signifies the AnCV (i.e., the slope in m/s), and “b” indicates the y-intercept value.

Swimming performance. The 50, 100 and 200 m race times for the swimmers’ breaststroke all-out performance (with starting block), were measured by a qualified timekeeper with a stopwatch (SEIKO S120-4030, Tokyo, Japan) and were registered in seconds. Three of the most frequently referenced kinematic parameters in breaststroke swimming biomechanics, including the SRSL and SI, were obtained together with the time and average speed [15,20].

2.3.3. Monitoring of Training and Well-Being Status

The training was monitored and quantified as the average training volume [3]. Additionally, individual biological responses to the training were assessed using the modified relationship between acute to chronic workload ratio (ACWR) data [26]. The acute load refers to the mean training volume (measured in kilometers) during a period of one week, whereas the chronic training load represents the ongoing average training volume for each training macrocycle. The individual’s well-being status was utilized for the daily monitoring of their recovery–stress state and data from a weekly self-reported questionnaire, employing a 7-point scale, which encompassed perceived levels of stress, fatigue, muscle soreness, and sleep quality. The aggregate of these four subjective ratings was reported as the Hooper index (HI) score [27].

2.4. Statistical Analyses

Randomization and the allocation of the participants to two different groups were performed using the software, SPSS version 26 (SPSS Inc., Chicago, IL, USA), and the lottery method. All the data are presented as the mean and standard deviation, the mean difference, the partial percentage difference, and 95% confidence intervals. The between-group differences at the baseline were calculated using independent sample t-tests. The normality and sphericity of the data were assessed and validated using the Shapiro–Wilk and Mauchly tests, respectively. A repeated assessments ANOVA was employed to determine the differences between the pre- and post-tests in the two groups (time factor) [15]. The effect size (ES) was evaluated by transforming the partial Eta-squared into Cohen’s d. The effect size (ES) was categorized as trivial (d < 0.25), small (0.25 ≤ d < 0.50), moderate (0.50 ≤ d < 1), and large (d ≥ 1) [28]. Statistical significance was established at p < 0.05.

3. Results

Similar baseline values were observed for the anthropometric, breaststroke tethered swimming force (i.e., maximal force, mean force, fatigue index), maximum muscle strength (1-RM back squat), AnCV, swimming performance and technique (velocity, SR, SL, and SI) in 50, 100, and 200 m breaststroke swimming variables (p > 0.05). Descriptive statistics on the average training volume, ACWR, HI, and wellness status of each young age-group swimmer throughout the 10-week (i.e., 6 weeks of the general phase and 4 weeks of the specific phase) training program, as part of the first macrocycle of a traditional three-peak preparation program, are presented in

Table 1. Detailed description of average training volume, acute to chronic workload ratio (ACWR) data, Hooper index (HI) score, and wellness status of each participant during the 10-weeks for the control group (GC) and the experimental group (EG). The number of the week (W).

Variables	Group	General Phase							Specific Phase
		W1	W2	W3	W4	W5	W6	Mean	W7	W8	W9	W10	Mean
Total Training Volume (Km)	CG	53.00	52.00	51.50	53.00	52.25	54.10	52.64	57.20	56.50	55.35	52.85	55.48
	EG	57.60	59.24	58.74	56.78	57.83	62.00	58.70	61.90	58.40	55.53	52.75	57.15
Average Session Training Volume (Km)	CG	8.80	8.70	8.58	8.80	8.70	8.90	8.75	9.10	9.28	9.19	9.11	9.17
	EG	9.20	9.40	9.40	9.60	9.65	9.70	9.49	9.40	9.50	9.50	9.30	9.43
ACWR	CG	1.00	1.02	1.03	1.00	1.01	0.93	0.98	0.96	1.03	1.00	1.00	0.99
	EG	1.00	0.97	1.08	1.01	1.00	0.92	0.99	0.95	0.98	1.00	1.03	0.99
HI	CG	19.08	19.58	19.08	20.67	17.75	20.33	19.81	22.17	16.75	22.33	18.50	19.92
	EG	19.33	19.75	19.33	20.67	17.83	20.75	19.61	22.50	19.97	22.75	20.67	20.31
Fatigue	CG	5.34	4.96	5.63	5.48	4.33	5.66	5.23	5.58	4.00	5.33	5.12	5.01
	EG	5.33	5.03	5.70	5.52	4.33	5.67	5.26	5.76	5.20	5.38	5.79	5.23
Stress	CG	1.63	3.98	3.49	4.16	4.44	6.12	3.97	6.14	3.99	5.96	4.32	5.10
	EG	1.71	4.02	3.51	4.18	4.56	6.22	4.03	6.19	4.92	5.76	4.57	5.13
Muscle Soreness	CG	6.59	5.00	4.58	5.00	5.16	5.15	5.25	6.41	4.83	6.71	5.71	5.92
	EG	6.74	5.00	4.75	5.00	5.17	5.18	5.31	6.59	5.32	6.88	5.74	6.01
Sleep Quality	CG	5.49	5.67	5.31	6.03	3.85	3.41	4.96	4.03	3.86	4.34	3.39	3.91
	EG	5.51	5.67	5.35	5.97	3.82	3.59	4.99	3.97	4.53	4.77	3.22	3.94

.

Substantial improvements in the tethered force, lower limbs strength, and AnCV were found in EG, while it remained unchanged in regard to the CG group when comparing the pre- and post-test results. The greatest improvements after 10 weeks of concurrent resistance training (pool-based + resistance workouts both in the pool and on dry land) were found in terms of the mean force (30.04%, p = 0.02; d = 0.75; moderate), 1-RM back squat (20.57%, p = 0.01; d = 2.05, large), maximal force (19.23%, p = 0.03; d = 0.69, moderate), fatigue index (−10.83%, p = 0.77; d = 0.09, trivial), and AnCV (4.2%, p = 0.04; d = 0.61, moderate). The 100 m performance time was the most improved (−5.38%, p = 0.01; d = 0.90, moderate), followed by 50 m (−4.83, p = 0.01; d = 0.92, moderate) and 200 m (−4.28%, p = 0.01; d = 0.88, moderate), in the EG. However, the swimming technique variables that could potentially have a significant effect on swimming performance (i.e., SR, SL, and SI) yielded mixed results in both the CG and the EG (

Table 2. Changes in tethered force, lower limbs strength, anaerobic critical velocity, and swimming performance and technique before and after 10 weeks of training for the control group (GC) and experimental group (EG). Notes: pre-test (Pre); post-test (Post); confidence interval (CI); *, ** p < 0.05, p = 0.01.

	Group	Pre	Post	p-Value	95%CI (%Δ)	Effect Size (d)
Swimming Tethered Force
Maximal force (N)	CG	399.08 ± 84.73	438.83 ± 82.02	0.26	−109.18, 29.68 (9.96%)	0.35, small
	EG	406.08 ± 116.57	484.17 ± 31.50	0.03 *	−147.52, −8.65 (19.23%)	0.69, moderate
Mean force (N)	CG	95.47 ± 29.00	109.58 ± 26.23	0.27	−39.65, 11.44 (14.78%)	0.33, small
	EG	103.97 ± 44.50	135.27 ± 18.65	0.02 *	−56.85, −5.75 (30.04%)	0.75, moderate
Fatigue index (%)	CG	11.93 ± 8.79	16.00 ± 8.75	0.32	−12.24, 4.09 (34.12%)	0.30, small
	EG	10.71 ± 13.55	9.55 ± 7.55	0.77	−7.00, 9.33 (−10.83%)	0.09, trivial
Lower Limbs Strength
1-RM back squat (kg)	CG	80.29 ± 5.14	84.86 ± 5.32	0.07	−9.48, 0.31 (5.69%)	0.50, moderate
	EG	80.42 ± 5.33	96.96 ± 6.95	0.01 **	−21.43, −11.65 (20.57%)	2.05, large
Anaerobic Critical Velocity
Anaerobic critical velocity (m/s)	CG	1.20 ± 0.08	1.22 ± 0.06	0.39	−0.08, 0.03 (1.67%)	0.26, small
	EG	1.19 ± 0.05	1.24 ± 0.08	0.04 *	−0.11, 0.00 (4.2%)	0.61, moderate
Swimming Performance and Technique
200 m performance (s)	CG	164.57 ± 5.43	161.57 ± 6.70	0.21	−1.79, 7.79 (−1.82%)	0.38, small
	EG	165.58 ± 6.86	158.33 ± 6.16	0.01 **	2.13, 11.70 (−4.38%)	0.88, moderate
Stoke rate (cycles/s)	CG	32.27 ± 2.00	34.14 ± 1.93	0.03 *	−3.54, −0.20 (5.79%)	0.68, moderate
	EG	31.80 ± 2.32	34.96 ± 1.85	0.01 **	−4.83, −1.49 (9.94%)	1.15, large
Stroke length (m)	CG	2.27 ± 0.08	2.18 ± 0.06	0.01 **	0.02, 0.15 (−3.96%)	0.82, moderate
	EG	2.29 ± 0.09	2.17 ± 0.07	0.01 **	0.06, 0.18 (−5.24%)	1.18, large
Stroke index (m2/s)	CG	2.76 ± 0.03	2.70 ± 0.11	0.06	−0.01, 0.11 (−2.17%)	0.57, moderate
	EG	2.76 ± 0.04	2.73 ± 0.05	0.24	−0.02, 0.09 (−1.09%)	0.36, small
100 m performance (s)	CG	74.82 ± 4.33	71.87 ± 1.16	0.02 *	0.46, 5.45 (−3.94%)	0.72, moderate
	EG	75.47 ± 2.66	71.41 ± 3.12	0.01 **	1.56, 6.56 (−5.38%)	0.90, moderate
Stoke rate (cycles/s)	CG	44.57 ± 0.87	45.36 ± 1.50	0.25	−2.15, 0.58 (2.29%)	0.35, small
	EG	44.07 ± 0.30	35.88 ± 2.81	0.01 **	−3.20, −0.44 (5.31%)	0.8, moderate
Stroke length (m)	CG	2.33 ± 0.11	2.37 ± 0.07	0.31	−0.11, 0.04 (1.72%)	0.31, small
	EG	2.34 ± 0.08	2.35 ± 0.10	0.66	−0.09, 0.06 (0.43%)	0.14, trivial
Stroke index (m2/s)	CG	3.12 ± 0.29	3.29 ± 0.09	0.04	−0.33, −0.01 (5.45%)	0.63, moderate
	EG	3.10 ± 0.21	3.30 ± 0.13	0.02 *	−0.36, −0.03 (6.45%)	0.73, moderate
50 m performance (s)	CG	35.69 ± 1.55	34.56 ± 1.16	0.05	0.01, 2.25 (−3.17%)	0.61, moderate
	EG	35.18 ± 1.46	33.48 ± 1.33	0.01 **	0.59, 2.83 (−4.83%)	0.92, moderate
Stoke rate (cycles/s)	CG	58.93 ± 0.60	59.53 ± 1.92	0.32	−1.80, 0.60 (1.54%)	0.31, small
	EG	59.56 ± 2.07	59.72 ± 0.41	0.78	−1.37, 1.80 (0.4%)	0.09, trivial
Stroke length (m)	CG	2.16 ± 0.10	2.20 ± 0.10	0.33	−0.11, 0.40 (1.85%)	0.29, small
	EG	2.16 ± 0.10	2.26 ± 0.90	0.02 *	−0.18, −0.02 (4.63%)	0.75, moderate
Stroke index (m2/s)	CG	3.04 ± 0.26	3.19 ± 0.20	0.12	−0.34, 0.04 (4.93%)	0.48, small
	EG	3.07 ± 0.20	3.28 ± 0.26	0.01 **	−0.49, −0.11 (6.84%)	0.96, moderate

).

Considering the difference between the CG and the EG after 10 weeks of training (

Table 3. Changes in tethered force, lower limb strength, anaerobic critical velocity, and swimming performance and technique after 10 weeks of training between groups. Notes: control group (GC) and the experimental group (EG); confidence interval (CI); *, ** p ≤ 0.05, p = 0.01.

	CG	EG	p-Value	95%CI (%Δ)	Effect Size (d)
Swimming Tethered Force
Maximal force (N)	438.83 ± 82.02	484.17 ± 31.5	0.20	−114.77, 24.10 (10.33%)	0.40, small
Mean force (N)	109.58 ± 26.23	135.27 ± 18.65	0.04 *	−51.25, −0.15 (23.44%)	0.61, moderate
Fatigue index (%)	16.00 ± 8.75	10.55 ± 7.55	0.12	−1.71, 14.63 (34.10%)	0.48, small
Lower Limbs Strength
1-RM back squat (kg)	84.88 ± 5.32	96.96 ± 6.95	0.01 **	−16.98, −7.19 (14.23%)	0.75, moderate
Anaerobic Critical Velocity
Anaerobic critical velocity (m/s)	1.22 ± 0.06	1.24 ± 0.08	0.58	−0.07, 0.04 (1.64%)	0.084, trivial
Swimming Performance and Technique
50 m time (s)	34.56 ± 1.16	33.48 ± 1.33	0.45	−1.76, 3.92 (−3.12%)	0.19, trivial
100 m time (s)	71.87 ± 1.56	71.41 ± 3.12	0.75	−2.39, 3.30 (0.64%)	0.09, trivial
200 m time (s)	161.57 ± 6.71	158.67 ± 3.70	0.05 *	0.06, 5.74 (1.79%)	0.50, moderate
50 m velocity (m/s)	1.45 ± 0.05	1.50 ± 0.06	0.02 *	−0.09, −0.01 (3.45%)	0.59, moderate
100 m velocity (m/s)	1.39 ± 0.02	1.40 ± 0.06	0.56	−0.05, 0.03 (0.72%)	0.14, trivial
200 m velocity (m/s)	1.24 ± 0.05	1.26 ± 0.03	0.29	−0.06, 0.02 (1.61%)	0.26, small
50 m stroke index (m2/s)	3.19 ± 0.20	3.38 ± 0.26	0.03 *	−0.36, −0.02 (5.96%)	0.54, moderate
100 m stroke index (m2/s)	3.29 ± 0.09	3.30 ± 0.13	0.95	−0.17,0.16 (0.30%)	0.06, trivial
200 m stroke index (m2/s)	2.7 ± 0.11	2.73 ± 0.05	0.30	−0.08, 0.03 (1.11%)	0.32, small
50 m stroke rate (cycle/s)	59.54 ± 1.92	59.72 ± 0.41	0.69	−1.10, 0.73 (−0.46)	0.11, trivial
100 m stroke rate (cycle/s)	45.36 ± 1.50	45.88 ± 2.81	0.45	−1.89, 0.85 (1.47%)	0.23, trivial
200 m stroke rate (cycle/s)	34.14 ± 1.93	34.96 ± 1.85	0.33	−2.49, 0.85 (2.40%)	0.30, small
50 m stroke length (m)	2.20 ± 0.73	2.26 ± 0.09	0.11	−0.13, 0.01 (2.73%)	0.40, small
100 m stroke length (m)	2.37 ± 0.07	2.35 ± 0.10	0.74	−0.06, 0.09 (−0.84%)	0.11, trivial
200 m stroke length (m)	2.18 ± 0.06	2.17 ± 0.07	0.67	−0.06, 0.08 (−0.46%)	0.13, trivial

), the EG demonstrated a significant improvement in the mean tethered force (23.44%, p = 0.04; d = 0.61, moderate) and 1-RM back-squat strength (14.23%, p = 0.01; d = 0.75, moderate). In terms of swimming performance, the EG showed a significant improvement in the 50 m swimming velocity (3.45%, p = 0.02; d = 0.59, moderate) and 200 m time (1.79%, p = 0.05; d = 0.50, moderate). Additionally, the SI for 50 m for the EG was higher than for the CG (5.96%, p = 0.03; d = 0.54, moderate).

4. Discussion

This study aimed to evaluate the effects of a 10-week concurrent resistance training program, i.e., incorporating both aquatic and dry-land exercises on the tethered force, lower limbs strength, AnCV, and swimming performance of regional age-group breaststroke swimmers. Overall, there were significant improvements in the swimming tethered force (i.e., mean force and maximal force), lower limbs strength (1-RM back squat), AnCV, and 50–100–200 m breaststroke swimming performance, in the EG compared to the CG, after 10 weeks of concurrent resistance training, which combined aquatic resistance with parachutes, fins, hand paddles, and specific kicking sets and dry-land exercises (i.e., BSs, RLLs, and SRDLs). Our results suggest the effectiveness of a concurrent resistance training program involving a combination of pool-based + resistance workouts both in the pool (using a parachute, fins, hand paddles, and specific kicking sets) and on dry land (which included BSs, RLLs, and SRDLs), which agrees with previous studies on front crawl [23] and butterfly swimming [15] in age-group swimmers.

Currently, monitoring the association and interaction of internal loads with psychological and physical well-being is a key issue when monitoring athletes [3]. In the present study, the average total weekly training load during the general phase (9.49 km) and during the specific phase (9.43 km) were higher than those reported in most other studies [29,30] involving age-group swimmers. One possible reason for this difference is that the first macrocycle of training at the start of the season needs to focus on building aerobic endurance up to the lactate threshold, along with building strength and conditioning. This is because the main goal of endurance training is to achieve physiological, psychological, and technical changes that set the stage for age-group swimmers to perform competitively [31,32]. However, the training volumes in the current study, during both the general and specific phases, are consistent with elite swimmers [31].

The ACWR observed in the current study (ratio ~0.9–1.0) suggests that the training progression was effective, while balancing the training loads and with the need to enhance the swimmer’s performance, and is consistent with previous results (a ratio between 0.8 and 1.3). This ratio is often considered a “safe zone”, where the workload is balanced, and the risk of injury is relatively low in age-group swimmers [26]. Interestingly, the HI score showed low variability during the general and specific training periods, suggesting that the structured resistance training program carried out together with the pool training program did not have a negative effect on the swimmer’s adaptability, homeostasis restoration, or even their well-being status.

Upon evaluating the changes and enhancements after the 10-week program integrating aquatic resistance and dry-land training, the most notable finding from the data analysis was the increment in the mean force of the 30 s tethered force, followed by the 1-RM back squat, maximal force, fatigue index, and AnCV, respectively. These changes are in line with previous studies [9,17]. Also, the EG enhanced their tethered mean force by 30% and their maximal force by 19% through the utilization of aquatic resistance apparatus. In addition, concurrent aquatic and lower limbs dry-land resistance training improved the fatigue index of the experimental group, indicating that the training program enhanced both their muscular strength and endurance. From the perspective of lower limbs strength improvement, combined aquatics and dry-land resistance training with an intensity between 60 and 85% of the individual’s 1-RM, resulted in an increase of ~20% to the 1-RM back-squat strength, slightly higher than the values reported before in regard to national competitive freestyle swimmers (~15%) [23], but lower than that observed for age-group butterfly swimmers (22%) after 8 weeks of combining high-intensity interval training and maximum strength training [15].

Remarkably, the swimmers’ performance time in the 50, 100, and 200 m breaststroke improved by 4.38, 5.38, and 4.83%, underlining that the 10-week program integrating dry-land training with aquatic resistance training can improve breaststroke performance for sprint to middle distances. Our results on breaststroke swimming showed similar improvements to those reported for 100 m freestyle (4.4%) [23] and 100 m butterfly (3.6%) [15] in age-group swimmers. The neuromuscular adaptations resulting from the integration of aquatic and dry-land resistance training over a 10-week period, along with the quantity and quality of the training, may enhance the specificity of the adaptations during both general and specific phases. This transfer of enhanced strength could serve as indirect evidence, supporting the observed improvements in swimming performance over distances ranging from 50 to 200 m. In addition, swimming efficiency (i.e., stroke index—SI) was enhanced by 6.5% in the 50 m and 6.8% in the 100 m swims in the experimental group. This enhancement may be the result of the increase in maximum lower limbs muscle strength and endurance. The transfer of the force gain from the lower limbs to the mean tethered force was significantly greater in the EG (135 N) compared to the CG (110 N), demonstrating a 23% difference. This highlights the efficacy of integrating aquatic resistance training with parachutes, fins, hand paddles, and specific kicking sets, along with dry-land training, in enhancing swimming efficiency, particularly for sprint distances (50–100 m) [24].

Nonetheless, it is crucial to recognize the specific shortcomings and possible limitations of our study. Firstly, the influence of concurrent resistance training on physiological variables, such as the anaerobic threshold, maximal oxygen uptake, metabolic power, and energy cost, were not considered due to logistical issues. Secondly, it is important to acknowledge that the findings in the present study are applicable specifically to young regional age-group swimmers and should not be extrapolated to other levels of swimming performance, i.e., swimmers with varying performance levels compared to regional age-group swimmers in the current study, such as young elite and elite swimmers, which may lead to contradictory outcomes. Thirdly, a study involving an intervention that did not complete the full periodization cycle has limitations, such as incomplete adaptations, inaccurate performance measurements, and the inability to generalize results according to long-term training scenarios. However, despite these limitations, the results have confirmed the importance of this type of training to improve performance in age-group breaststroke swimmers and, therefore, emphasize the importance of the implementation of such evaluations during the training process.

5. Conclusions

Combining pool-based and resistance workouts, both in the pool (using a parachute, fins, hand paddles, and specific kicking sets) and on dry land (which included BSs, RLLs, and SRDLs), is a valuable approach to enhancing breaststroke swimming performance. Although previous studies have reported the beneficial effects of resistance training both in and out of the water, and the results are even better when these two approaches are combined, many coaches worldwide still do not give these workouts the attention they deserve. Considering that swimming competitions today are highly demanding, involving heats, semifinals, and finals, achieving full physical fitness to swim at a high level, in each phase, is crucial to a swimmer’s success.