The Effect of Plyometric Training on the Speed, Agility, and Explosive Strength Performance in Elite Athletes

Abstract

The purpose of this study was to evaluate the speed, agility, and explosive strength performance of elite basketball players over an 8-week plyometric training program. Fifteen elite male college basketball players in Taiwan (average age 22.16 ± 0.85 years old) were publicly recruited. All participants received 24 plyometric training courses three times per week for 8 weeks, and the courses were implemented pre- and post-test. The speed and agility test items were divided into a 20 m sprint and a T-shaped run. In the explosive strength test, a force plate was used to measure countermovement jump to understand the pre- and post-test differences in all the test indicators, including the rate of force development, time of the rate of force development, ground reaction forces for the moment of jumping, duration of passage, and jump height. It was found that, after the participants underwent the plyometric training program, the body mass index and body fat percentage were significantly reduced, the skeletal muscle mass was significantly increased, and the post-test scores for speed and agility improved significantly. All the participants exhibited a steeper gradient for the rate of force development (r = −0.816~−0.963) and a shorter time for the rate of force development (0.107~0.232 s). The ground reaction forces reached 1509.61~2387.11 Newtons. The duration of passage reached 0.643 s, and the jump height reached 0.624 m. The conclusion was that the plyometric training program can increase muscle volume in the lower limbs and legs, increase the rate of force development, and shorten the jumping time, thereby enhancing explosive strength.

1. Introduction

In addition to special skills, many sports teams must also have sports-specific physical fitness [1,2]. These so-called special skills refer to sports-specific physical fitness, which means that athletes have the appropriate muscle strength and physical fitness for specific sports [3,4], also called “special physical fitness to improve technical performance”. Through special physical training, strength and explosive strength can be improved. This is one benefit of special physical training. For example, not only basketball skills such as dribbling and layups, but also the athlete’s own sports quality, such as body extensibility, muscle strength, speed, agility, explosive strength, and other special physical abilities, will affect the performance of athletes [5,6].

In addition to specific sports skills, basketball players must have comprehensive aerobic and anaerobic physical fitness [7,8,9,10]. Research has shown that basketball players can cover a maximum of 5 km in one game [11], indicating that about 57% of the game time is walking and 9% of the time is stationary [12]; this demonstrates the aerobic metabolic requirements in basketball. Some people think that basketball is an intermittent high-intensity sport that mainly requires anaerobic metabolism [13,14]. However, half of the time spent playing basketball is aerobic exercise, but the time spent performing anaerobic exercise often involves instant dribbling, emergency stop–jump shots, quick layups, and instant takeoffs to compete for rebounds. This shows that repeated sprinting, agility (change in direction and speed), and jumping are essential qualities for basketball players [15].

Muscle strength training can be divided into bare-hand fitness (a no-equipment workout), barbells, equipment, and plyometric training (PT); many fitness coaches design variety PT to apply to athletes’ training [16,17,18,19]. The term “plyometric” means fast and powerful sports performance [20]. It is a form of explosive training that can improve the force rate and neural response as well as agility and speed [21]. The principle of PT is based on the stretch–shorting cycle, or SSC for short [16]. Plyometric training uses the mutual coordination of muscle concentric contraction and eccentric contraction so that the muscles and connective tissues can fully store elastic potential energy and then use the stretch reflex principle to instantly and rapidly concentrically contract, release stored elastic potential energy, and generate powerful explosive strength [22]. Explosive strength is the momentary muscle strength that directly affects sports performance; the quality of explosive strength is key to sports performance [23].

Compared with the duration of an entire basketball season and the number of games, there is a preparation period of about half a year. During this period, players must practice tactics and perform personal technical training and special physical training; the time to perform muscle strength training is limited. In particular, muscle strength training is related to personal physical fitness and affects the technical performance of players [24,25,26,27]. Therefore, coaches must fully focus on all aspects of training, including endurance, strength, explosive strength, speed, and jumping. Therefore, it is necessary to design new training programs to cultivate the best physical fitness of players in the shortest time. In recent years, PT has become an indispensable training method for elite athletes in various countries around the world [28,29,30,31,32]; it is an important training method for sports strength, jumping performance, and injury prevention [33], although the prerequisite is that the trainee should have basic muscle strength. Previous PT study protocols have varied in timing, frequency, and intensity: typically, plyometric training is performed for 6 to 12 weeks with a training frequency of 1–3 times per week at maximal to near-maximal strength [34]. PT is beneficial for enhancing the explosive strength of athletes, although many fitness coaches can only record the jump height through a “Vertec vertical takeoff measuring device”. For elite athletes, more in-depth testing is required, such as the rate of force development (RFD), ground reaction forces (GRFs), duration of passage, and jump height. Therefore, this study used a sports science force plate for detection, which could specifically present the values related to explosive strength.

According to the literature, due to the small number of PT studies on elite athletes (compared with the number of studies on general athletes), it is necessary to further understand whether PT can also benefit this group and accurately test the sports science equipment to facilitate the planning of accurate training courses. The purpose of this study was to evaluate the speed, agility, and explosive strength performance of elite basketball players over an 8-week PT program. The hypotheses are proposed as follows. Hypothesis one: 8 weeks of a PT program can improve the speed and agility of elite athletes. Hypothesis two: 8 weeks of a PT program can improve the explosive strength of elite athletes.

2. Materials and Methods

In this study, 15 elite male college basketball players were measured twice in single groups of pre- and post-tests. This study’s design was quasi-experimental [35]; a PT program was implemented between the pre- and post-tests.

2.1. Research Participants

This study openly recruited 15 male college basketball players in Taiwan (average age 22.16 ± 0.85 years old). The participants were male basketball players from Taiwan’s university first division (the first division represents the elite level); all participants were able to make decisions of their own volition; those who were unable to participate because of age, mental, or physical condition or due to circumstance, status, or social and economic conditions were excluded. The recruited participants were first tested for background variables, including age, weight, height, body mass index (BMI), skeletal muscle mass (SMM), and body fat percentage (BFP). The intraclass correlation coefficients (ICCs) of the ages of the 15 participants in this study were estimated in two ways: single measures and average measures. However, in order to analyze the correlation between each researcher, the estimation of single measures was selected, and the results of this test were evaluated for repeatability. The results showed that the correlation between the 15 participants was high, ICC = 0.836 (p < 0.001), with good repeatability and consistency. All participants signed the informed consent form according to their personal wishes in line with scientific and ethical principles (contents included no orthopedic disease or heart disease; can perform daily life without assistance; and willing to not take drugs that can increase muscle during the study period). This study was approved by the Jen-Ai Medical Foundation Dali Jen-Ai Hospital: Human Body Research Ethics Committee, approval number 110-96.

2.2. Research Materials

Referring to Slimani et al.’s study on the effects of PT on team athletes’ physical fitness [22], the PT program for this study was developed. All participants received a PT program 3 times per week for 8 weeks (24 sessions). The main movements included vertical and horizontal jumping movements and full-body-weight training. The exercise intensity in this study is shown as the metabolic equivalent (MET). The so-called MET is defined as the consumption of 3.5 milliliters of oxygen per kilogram of body weight per minute, which is roughly equivalent to a person sitting in a quiet state without performing any activity. An oxygen consumption of 4METs activity means that the oxygen consumption during exercise was 4 times greater than that of the resting state, i.e., 480 calories were consumed (4METs × 1.5 h × 80) [36]. In this study, low to high intensity was implemented, around 4.0–6.0 METs; the higher the intensity, the more effort and rapid breathing required by the participants. The participants rested for 10–30 s after completing each operation and rested for 3–5 min after completing all items in one cycle; in total, three cycles were required [37]. The 8-week PT program was divided into three phases of varying intensities. A low-intensity design (10 repetitions of one action, 4METs) was adopted in the 1st and 2nd weeks; a medium-intensity design (8 repetitions of an action, 5METs) was adopted in the 3rd to 5th weeks; and a high-intensity design was adopted in the 6th to 8th weeks. The intensity designs followed the pattern of 6 repetitions per set at 6METs. The content of this training was designed according to a step-by-step principle. The training intensity of each stage increased, but the number of repetitions decreased, as shown in

Table 1. Participants implementing a PT program.

Phase 1 (Weeks 1 to 2)	Phase 2 (Weeks 3 to 5)	Phase 3 (Weeks 6 to 8)
10 items, repeated 3 rounds, 4METs	12 items, repeated 3 rounds, 5METs	12 items, repeated 3 rounds, 6METs
- Jump forward 15 m with both feet - Jump 15 m left and right and forward - Jump rope ladder - Jump 15 m forward with one foot - Cross-ball side jump - In-place jump and clap - Quickly up and down the first step (30 s 17 times) - Fast up and down stairs (3 steps in one foot, fast running to the next step) - Kneeling machine 80% (10 times) - Core lifts 70% (front squat, parallel squat, 8 times each) - Smith lower-limb squat 70% (10 times)	- One foot forward jump 15 m - Jump 15 m left and right and forward - 90 degree jump and turn - 180 degree jump and turn - In-place jump and clap - In-place kneeling and one foot jump - Fast up and down stairs (3 steps in one foot, fast running to the next step) - Fast up and down stairs (two feet step on the two feet, fast run to the next step) - 10 Kg dumbbell goblet squat - 50 CM wooden box jumps up and down - Kneeling machine 90% (8 times) - Core lifts 80% (front squat, parallel Squat, 8 times each) - Smith lower-limb squat 80% (8 times)	- High knees - Jump lunges - Jump lunge squat combo - Long jumps - Snowboarder jumps - Squat jumps - Tuck jumps - Fast up and down stairs (two feet step on the two feet, fast run to the next step) - 60 CM wooden box 8 consecutive squat jumps - Kneeling machine 100% (5 times) - Core Lifts 90% (front squat, parallel squat, 5 times each) - Smith lower-limb squat 90% (5 times)

.

2.3. Test Method

2.3.1. Body Composition Detection

Body composition was measured using an InBody 520 (Biospace Co., Ltd., Seoul, Korea). The InBody 520 estimates a person’s body composition based on bioelectrical impedance analysis (BIA). Bioimpedance is useful in body composition studies because electrodes make contact with the body to measure the resistance value (impedance) through an electrical current (Ward, 2019). Participants stand on the InBody 520, facing forward, and stand upright for approximately 60 s. Finally, the body mass index (BMI), body fat percentage (BFP), and skeletal muscle mass (SMM) were determined from the results of the body composition analysis.

2.3.2. Speed and Agility Test

All participants underwent 8 weeks of the PT program. All participants took a pre-test the day before training and a post-test a day after 8 weeks of training. The speed test items were a 20 m sprint and a T-shaped run. The test time of different items had to be at least 10 min apart, and the same item was tested twice with intervals of at least 3 min each time.

1. The 20 m sprint: The unit was in seconds, taken to two decimal places; the test was performed twice, and the best score was recorded.

2. The-shaped run: Participants ran back and forth; the T-shaped four-point distance started from the bottom of the T. After blowing a whistle, the participants started to run forward for 15 m to the T-shaped crossing point and then quickly turned 90 degrees to the left and ran another 15 m. Participants touched the second point with their finger, then turned 180 degrees and ran for 30 m; they then touched the third point with their finger. Subsequently, participants ran back to the intersection and finally ran back to the starting point. The T-shaped run was performed 4 times. The time was measured in seconds, to two decimal places. The whole test was performed twice, and the best score was recorded.

2.3.3. Explosive Strength Test

This study used PASCO scientific apparatus, manufactured by Roseville, California, USA. PASCO scientific equipment is a voltage-sensing force plate; this device could work in the laboratory and remotely (with Bluetooth and tablet connection) [38]. The biaxial force plate was adjusted to perform vertical and front-to-back force analyses. In evaluations of the load capacity of a force plate in human movement, the apparatus should be able to withstand the landing of the heaviest person from significant heights after they jump [39]. The sampling frequency of the equipment was set to 1000 Hz (or 1 kHz) so that 1000 force measurements were generated per second. The force plate was used to measure participants’ countermovement jump (CMJ) to understand the pre- and post-test differences in all test indicators, including the rate of force development (RFD), the time of RFD, ground reaction forces (GRFs) at the moment of jumping (unit: Newtons, N), the duration of passage (unit: seconds, s), and jump height.

2.4. Control Variable

Top-level male college basketball players were openly recruited in Taiwan. The background variables of these participants included age, weight, and height. Some unconsidered factors or variables could potentially have influenced the findings in this study. For example, basketball players have different specialties and develop different muscle groups, which were the control variables in this study. In addition, the participants attended common basketball skills training on weekdays, and many athletes supplemented their diets with high protein to enhance daily muscle strength exercises. In this study, the use of high-protein supplements was prohibited for 8 weeks, which was another control variable.

2.5. Statistical Analysis

For the 15 participants, a quantile–quantile (Q–Q) plot in SPSS was used to judge normality [40], and analysis of variance (ANOVA) was used to test the homogeneity [41]. The pre- and post-test raw data were obtained and presented as standard deviations (SD) and means (mean) [42]. Additionally, the intraclass correlation coefficient (ICC) reliability analysis method in SPSS was adopted in order to determine the correlation of the participant’s ages (ICC value between 0 and 1). An ICC value less than 0.4 indicated poor repeatability or consistency; an ICC value greater than 0.75 indicated good reproducibility or consistency [43]. t-tests were used to compare all the differences between pre- and post-tests, and the overall significance level was set at p < 0.05; SPSS 20.0 software (IBM^®, Armonk, NY, USA) was used for statistical analysis of the data in this study.

3. Results

3.1. Participant Normality, Homogeneity, and Background Variable Analysis

Normality was judged using quantile–quantile (Q–Q) plots. Both the abscissa and the ordinate in these graphs use quantiles; therefore, the abscissa is the normal quantile, and the ordinate is the quantile of the actual data. Thus, the Q–Q plot was utilized to compare the gap between the theoretical quantile and the actual quantile. If there were no differences, all points would be on a straight line (from the bottom left to the top right); otherwise, it would deviate from the straight line. The 15 participants in this study could be considered normal, as shown in Figure 1. For original data of the age, height, and weight of 15 participants, analysis of variance (ANOVA) was used for normality and homogeneity analyses. The F value of the test results was 0.924 (p > 0.05), and there were no significant differences in the variance among the three, showing homogeneity.

For the 15 participants in this study, after 8 weeks of the PT program, the mean BMI, SMM, and BFP values of all participants were significantly different (p < 0.05) at the pre- and post-tests, as shown in

Table 2. Background variable analysis of the participants.

Serial Number	Age (Years)	Height (cm)	Weight (kg)	BMI 1 (kg/m2)		SMM 1 (kg)		BFP 1 (%)
				Pre-Test	Post-Test	Pre-Test	Post-Test	Pre-Test	Post-Test
1	23.25	174.7	83.6	27.39	25.84	41.22	43.19	21.26	18.35
2	21.61	176.7	75.6	24.21	23.67	43.72	45.28	13.75	11.86
3	21.96	186.6	74.5	21.39	21.15	45.89	46.17	9.34	8.17
4	20.54	185.4	85.6	24.91	23.73	61.31	62.74	14.72	12.36
5	22.53	195.5	89.5	23.42	22.06	55.13	57.55	12.19	9.75
6	22.64	184.5	82.3	24.18	23.65	49.35	51.23	13.04	12.28
7	23.17	185.3	75.7	22.05	21.43	41.76	43.05	10.58	9.56
8	22.53	183.7	92.3	27.35	26.12	55.33	56.92	23.78	20.59
9	21.95	197.6	108.4	27.76	26.35	63.08	64.12	25.05	23.58
10	22.71	192.3	102.7	27.77	26.52	60.62	61.05	26.13	24.67
11	21.92	196.4	105.5	27.35	25.71	61.37	62.19	24.21	21.55
12	20.53	177.8	73.6	23.28	22.65	42.41	43.84	12.41	11.05
13	21.17	176.6	76.3	24.46	23.53	44.23	46.17	13.52	12.11
14	22.38	194.5	94.4	24.95	23.82	56.64	57.22	13.85	12.53
15	23.52	195.7	90.8	23.71	22.57	64.86	65.18	12.75	10.82
	22.16 ± 0.85	187.15 ± 7.17	87.66 ± 11.26	t = 8.61 * (0.000)		t = −7.37 * (0.000)		t = 10.15 * (0.000)

¹ BMI, body mass index; SMM, skeletal muscle mass; BFP, body fat percentage. Means ± standard deviations are presented as M ± SD. * t-test values are presented as t-values (p-values) p < 0.05.

. BMI is an estimated value used to measure obesity and body fat. In this study, young elite athletes were tested; the BMI values showed that they were all in the standard range. In particular, there was a positive linear correlation between BMI and BFP and a negative correlation between SMM and BFP; after the participants had undergone the PT program, the BMI and BFP values were significantly reduced, and SMM was significantly increased.

3.2. Pre- and Post-Test Results of Participants’ Speed and Agility

After 8 weeks of the PT program for the 15 participants, it was found that there were significant differences (p < 0.05) in the two tests of speed and agility in both the pre- and post-tests (p < 0.05), as shown in

Table 3. Pre- and post-test analysis of participants’ speed and agility.

Serial Number	Height (cm)	Weight (kg)	Speed (20 m Sprint), s				Agility (T-Agility Run), s
			Pre-Test	Post-Test	Progress 1 (%)	Grade	Pre-Test	Post-Test	Progress 1 (%)	Grade
1	174.7	83.6	3.31	3.17	4.23	5	9.93	9.65	2.82	12
2	176.7	75.6	3.01	2.96	1.66	13	9.06	8.23	10.26	1
3	186.6	74.5	2.98	2.94	1.34	15	9.38	8.68	7.46	5
4	185.4	85.6	3.29	3.15	4.26	4	9.41	9.23	1.91	15
5	195.5	89.5	3.49	3.38	3.15	10	10.63	9.82	7.62	4
6	184.5	82.3	3.32	3.21	3.31	9	9.39	9.12	2.88	13
7	185.3	75.7	3.03	2.97	1.65	14	9.23	8.56	7.26	6
8	183.7	92.3	3.73	3.54	5.09	2	10.07	9.82	2.48	14
9	197.6	108.4	3.86	3.71	3.89	6	11.35	10.71	5.64	7
10	192.3	102.7	3.82	3.68	3.63	8	10.62	10.13	4.61	10
11	196.4	105.5	3.75	3.61	3.73	7	11.14	10.58	5.03	9
12	177.8	73.6	3.01	2.93	2.66	12	9.11	8.31	8.78	2
13	176.6	76.3	3.04	2.95	2.96	11	9.15	8.37	8.52	3
14	194.5	94.4	3.58	3.42	4.67	3	10.54	9.95	5.59	8
15	195.7	90.8	3.61	3.38	6.37	1	10.21	9.86	3.43	11
t-value (p-value)			t = 8.99 * (0.000)				t = −9.18 * (0.000)

^1. Progress (%) refers to the percentage difference between the pre- and post-tests. * t-test values are presented as t-values (p-values) p < 0.05.

. Participant No. 15 achieved the highest improvement of 6.37% in the 20 m sprint. Participant No. 3 demonstrated the least improvement of only 1.34%, but their 20 m sprint was the fastest. In fact, No. 3 exhibited an excellent speed of 2.98 s in the pre-test, only leaving room for a slight improvement in the post-test: 2.94 s. Participant No. 15 demonstrated a speed of 3.61 s in the pre-test, then a greatly improved speed of 3.38 s in the post-test.

The pre- and post-tests of agility (T-agility run) showed that participant No. 2 demonstrated the highest level of improvement of 10.26%, and their T-agility was also the fastest. Participant No. 2 exhibited excellent agility in the pre-test, reaching 9.06 s; however, after the PT program, there was also a substantial improvement to 8.23 s. Participant No. 4 exhibited the worst improvement of only 1.91%. The agility of participant No. 4 in the pre- and post-tests only showed a slight improvement. However, the agility scores of participant No. 4 in the pre- and post-tests were at an average level across the participants.

The above results confirm that the 8-week PT program significantly improved the speed and agility of 15 elite male college basketball players. This confirms the acceptance of Hypothesis one: 8 weeks of a PT program can improve the speed and agility of elite athletes.

3.3. Pre- and Post-Tests of Participants’ Explosive Strength

This study used a PASCO scientific biaxial force plate, which connected laboratory equipment to remote equipment (via Bluetooth and tablet connection). Participants stood on the force plate to perform the countermovement jump (CMJ), then stood still on the force plate for a few seconds after they landed. The pre- and post-test results obtained by the force plate included the RFD, the time of the RFD, the GRF at the moment of jumping, the time in the air, and the jump height. After an 8-week PT program, it was found that there were significant differences (p < 0.05) between the pre- and post-tests, as shown in

Table 4. Data analysis of the CMJ via the force plate test ¹.

n	RFD, r		RFD, s		GRF at the Moment of Jumping, N			Duration of Passage, s			Jump Height, m
	Pre-Test	Post-Test	Pre-Test	Post-Test	Pre-Test	Post-Test	Progression (%)	Pre-Test	Post-Test	Progress (%)	Pre-Test	Post-Test	Progression (%)
1	−0.943	−0.951	0.124	0.121	1465.92	1529.98	4.37	0.503	0.541	7.55	0.310	0.391	26.13
2	−0.892	−0.911	0.127	0.124	1449.63	1526.14	5.28	0.560	0.591	5.54	0.413	0.472	14.29
3	−0.954	−0.963	0.113	0.107	1482.67	1561.71	5.33	0.604	0.643	6.46	0.545	0.624	14.50
4	−0.885	−0.914	0.138	0.131	1594.54	1678.53	5.27	0.579	0.611	5.53	0.459	0.518	12.85
5	−0.944	−0.952	0.122	0.118	1697.94	1753.62	3.28	0.531	0.582	9.60	0.352	0.431	22.44
6	−0.952	−0.961	0.120	0.117	1571.91	1616.33	2.83	0.556	0.582	4.68	0.377	0.468	24.14
7	−0.941	−0.952	0.119	0.114	1458.97	1524.29	4.48	0.572	0.619	8.22	0.411	0.470	14.36
8	−0.853	−0.865	0.235	0.224	1742.56	1813.42	4.07	0.465	0.521	12.04	0.262	0.331	26.34
9	−0.785	−0.823	0.227	0.221	2011.03	2387.11	18.70	0.451	0.489	8.43	0.253	0.331	30.83
10	−0.779	−0.816	0.226	0.219	1924.12	2123.42	10.36	0.471	0.512	8.71	0.277	0.345	24.55
11	−0.785	−0.823	0.227	0.221	1969.78	2256.27	14.54	0.484	0.533	10.12	0.284	0.363	27.82
12	−0.942	−0.953	0.118	0.112	1428.53	1509.61	5.68	0.587	0.624	6.30	0.512	0.584	14.06
13	−0.947	−0.951	0.120	0.115	1460.95	1514.43	3.66	0.575	0.611	6.26	0.486	0.554	13.99
14	−0.885	−0.911	0.195	0.191	1753.61	1826.50	4.16	0.536	0.584	8.96	0.353	0.456	29.18
15	−0.913	−0.934	0.187	0.175	1717.82	1809.67	5.35	0.548	0.569	3.83	0.368	0.443	20.38
	t = 5.987 * (0.000)		t = 8.513 * (0.000)		t = −4.538 * (0.000)			t = −15.801 * (0.000)			t = −23.926 * (0.000)

^1. The rate of force development is referred to as RFD (r); the ground reaction force is referred to as GRF (t); for the duration of passage, the unit is seconds (s). Progression (%) refers to the percentage difference between the pre- and post-tests. * t-test values are presented as t-values (p-values) p < 0.05.

. The force plate test showed the data of each participant; however, only the data for participant No. 1 are reported in this article, as shown in Figure 2 and Figure 3.

The time in seconds from the moment when the participant’s feet touched the ground to when the feet left the ground was referred to as the time spent in the RFD. In the pre-test, this was 0.113–0.241 s, and in the post-test, this was 0.107–0.232 s. The pre-test slope (r = −0.779~−0.954) and the post-test slope (r = −0.816~−0.963) show that the instantaneous explosive strength of the participants was at the level of elite athletes: participant No. 3 was the best. Their RFD had a post-test time of 0.107 s and a slope of −0.963. Due to the differences in the weight and muscle strength of the participants, the resulting GRF for the moment of jumping varied greatly. Overall, the pre-test GRF was 1428.53~2011.03 Newtons (N), and the post-test GRF was 1509.61~2387.11 N. In terms of the duration of passage, participants released their maximum force using rapid squat movements (momentary knee bends, arm swings, and reaction forces from jumping). After the participants had completed the PT program, participant No. 3 (0.643 s) demonstrated the longest duration of passage value. Comparing pre- and post-test results, the duration of passage of participant No. 8 (0.465~−0.521 s) improved the most (by 12.04%). In terms of jump height, according to the results of the force plate test, the average jump height of the overall participants showed a difference in the pre- and post-tests; each participant exhibited a significant improvement. Among them, participant No. 3 was the most exceptional; their CMJ height reached 0.624 m. In addition, participant No. 9 improved by 30.83%, from 0.253 m to 0.331 m, although participant No. 9 also recorded the lowest jumping height of all participants, which may be associated with their own body weight (the weight of participant No. 9 was the highest among all the participants).

The above results demonstrated that the 8-week PT program significantly improved the explosive strength of the 15 elite male college basketball players. This confirms the acceptance of Hypothesis two: 8 weeks of a PT program can improve the explosive strength of elite athletes.

4. Discussion

PT methods are widely used to improve muscle strength to generate explosive strength [31]. The results of this study, shown in Table 1, indicate that 8 weeks of a PT program could effectively improve the physical fitness of elite male basketball players. The BMI and BFP of all participants had decreased in the post-test results, and the SMM increased. This result is similar to many studies [8,9,44,45]. Increasing PT from low-intensity to high-intensity significantly increases aerobic and anaerobic fitness; after the 8-week program, the participants exhibited enhanced oxidative and glycolytic properties, their intrinsic SMM characteristics had changed, and some muscle fibers transformed into fast-twitch muscles, significantly increasing the SMM [22]. It has also been confirmed that the sports performance of muscle strength or explosive strength depends on muscle mass [4]. Similarly, because basketball players frequently jump, loading the antigravity muscles, many studies have reported the benefits of a shift in fiber type composition [46]. Thus, performing training results in a significant reduction in the fat percentage, accompanied by an increase in lean body mass [47].

Table 2 indicates that, comparing participants’ pre- and post-test values for the 20 m sprint and the T-agility run, the PT program was found to have a significant effect on the speed, agility, and explosive strength performance of elite college basketball players, consistent with many prior studies [17,27,32,48,49,50,51]. Some studies have identified that PT affects muscle length, strength, and flexibility to increase speed [52]; further studies have also demonstrated that the increase in muscle mass and muscle fiber hypertrophy caused by PT may lead to the increased speed of participants [53]. In this study, PT had a significant impact on agility. Some scholars have recognized that PT will affect muscle spindles, Golgi tendons, tendons, and body posture control [54], thereby improving agility in the participants [55]. Based on the above effects of PT on speed and agility, the results of this study confirm that PT had a positive impact on athletes’ jumping, sprint performance, and lower-body muscle strength and confirm the effectiveness of PT in improving agility (speed of changing directions) and sprinting in basketball players [10,19].

Table 3 shows the test results obtained with the force plate. It was found that PT improved the participants’ explosive strength. Comparing the pre- and post-test values in the experiment, the RFD, time of RFD, GRF at the moment of jumping, the duration of passage, and jump height all exhibited significant improvements. The RFD is the speed at which participants perform the CMJ to generate the maximum force, and the RFD is another important indicator for basketball players to enhance their sports performance. In this study, RFD could be regarded as the slope (r) of force–time, and the slopes for all participants in the post-test ranged from −0.816 to −0.963, showing that the slope of all participants was steep, presenting a centripetal force curve, indicating an excellent RFD, which was consistent with many other studies [56,57,58]. The time taken by the participants in this study was between 0.113 and 0.241 s. The length of time spent performing the RFD was in line with that of elite athletes, and it is worthy of further discussion. Research by Almosnino et al. pointed out that the time for an average person to exert all their strength to produce the maximum force time is approximately 400 milliseconds [59]. However, this is too long for many sports. For vertical jumping, the time allowed for the soles of the feet to be in contact with the ground is approximately 200 milliseconds [60]. Research by McMahon et al. pointed out that high jumpers can generate very powerful takeoff energy in a very short time of 0.1~0.2 s; the moment from when the jumper’s takeoff foot touches the ground to the moment when the takeoff foot leaves the ground is only 0.1~0.2 s [58], and many studies have also confirmed that having a better RFD could produce faster movements and greater explosive strength [61,62,63].

The momentary GRF values of participants No. 9, 10, and 11 in this study were the highest among all participants, but their RFD values were the lowest among all participants. This phenomenon shows that a strong GRF does not necessarily correspond with a good RFD [64] because the RFD is related to the contact time of the soles of the feet, and the GRF is related to body weight and muscle mass. Therefore, the variability in both was large, as evidenced in many studies [65,66,67]. In addition, the relationship between the RFD and the explosive strength of participants No. 9, 10, and 11 is confusing. The basis of explosive strength is muscle strength, and explosive strength determines the RFD performance [68]. RFD is derived from the force or the slope of the force–time curve of voluntary muscle contraction [69,70]; thus, the calculation formula of the RFD is as follows: RFD = force (moment) ÷ force time (time). Explosive strength refers to the ability to generate the maximum power in the shortest time, which is a result of the combination of speed and power [15]; thus, the formula for calculating explosive strength is as follows: explosive strength (P) = power (F) × velocity (V). RFD is associated with instantaneous time, and explosive strength is associated with speed; therefore, there was a discrepancy between the two, a view held by many scholars [71]. According to research, it takes approximately half a second (0.5 s = 500 milliseconds) for muscle contraction to reach maximum strength, and the ground contact time when running is within one-fifth of a second (0.20 s = 200 milliseconds) [63]; the faster the speed, the shorter the ground contact time, but the greater the strength required. Therefore, improving strength and shortening the RFD time is more important than developing maximum strength [72]. Thus, although maximizing strength has its benefits, developing maximal strength is not imperative for every sport. If technical aspects are not considered, those who can exert greater strength in a shorter period of time will have an opportunity to gain the upper hand [73]. Therefore, RFD relies on muscle contraction and is a key indicator of explosive strength.

The results of the CMJ experiment found that the duration of passage of participant No. 3 reached 0.643 s, and the jump height reached 0.624 m, which was the best performance among all participants, which showed that the PT program had some positive effects on improving explosive strength. These data corroborate that the reaction force generated in the CMJ remains for the 0.643 s duration of passage. After PT, it was found that the explosive strength of the lower limbs increased in the duration of passage, and the jump height increased [74,75]. Research by Stojanović et al. demonstrated that high explosive strength is composed of three factors: the size of the muscle cross-section, the stiffness of the muscle mass, and neural adaptation [76]. In this study, PT recruited the required motor units and stimulated the activation of motor nerves during training so as to quickly reach the maximum force; thus, the RFD, the duration of passage, and the jump height were enhanced. In addition, from the force plate operation, it was found that the muscle contraction of the participants before takeoff enabled the muscles to generate the energy required for movement. This energy was temporarily stored in the muscle cells. When the muscles contract rapidly to produce muscle stretching, the maximal force produced at this time improves the muscle explosive strength [5,77,78].

There were several limitations in this study. First, when the participants performed the CMJ action on the force plate, their feet had to be straight when they landed instantly; otherwise, the duration of passage may have been overestimated. At the moment of jumping, the speed of squatting, the angle of the knees and ankle joints, and the strength of swinging arms all affect the jump height. Finally, this research aimed to assess vertical in-place jumps. As for the takeoff height and the duration of passage, it cannot be estimated from the results of this study because the jump height and the duration of passage of moving players should also consider the players’ muscle strength and weight. Additionally, regarding speed, impulses plus muscle strength will affect the height of the instantaneous bounces performed during movement. A good jumping ability should also be combined with extensibility of the body in order to enable excellent stretching reflexes in the air. This study focused on the benefits of PT for performing basic vertical jumps. In the future, it is recommended to continue to study jumping performance during movement for different sports.

5. Conclusions

This study yields the following conclusions. After 8 weeks of a PT program, it was found that all the participants significantly improved their RFD(r), GRF at the moment of jumping, duration of passage, jump height, and the time of RFD. The PT program was beneficial for elite athletes to improve their body muscle mass, displacement speed, body agility, and lower-limb explosive strength. Moreover, the technical characteristics of basketball include speed, agility, and explosive strength training. Although explosive strength and speed improvements cannot be achieved in a short time, PT can increase the muscle mass of the lower limbs and legs, increase the RFD, and shorten the jumping time, thereby enhancing explosive strength. Therefore, PT should become part of the training program for elite basketball athletes, which is beneficial for sports quality and athletes’ performance.