The Effect of the Nordic Hamstring Curl Training Program on Athletic Performance in Young Football Players

Abstract

Background: This study aimed to determine the effect of the Nordic hamstring curl training (NHCT) program on athletic performance elements such as linear speed, change of direction (COD), jump performance (CMJ), and eccentric muscle strength (Nordic Hamstring Curl Breaking Point Angle—NHCBP) in young football players. Methods: The study group consisted of 40 male football players who were actively trained and had no previous eccentric training experience or reported any injuries. The participants were randomly divided into a training group (TG = 20) and a control group (CG = 20). The TG performed the NHCT program twice a week for eight weeks, in addition to their standard football training. The CG continued with standard football training. Results: The study findings revealed no statistically significant differences in the interaction between group and time in 10, 20, and 30 m sprint performance. However, statistically significant differences were found in CMJ performance in terms of group–time interaction (F = 19.99, p < 0.001, η² = 0.52), COD (F = 11.10, p < 0.004, η² = 0.38), and NHCBP (F = 6.14; p < 0.02; η² = 0.25). After the eight-week NHCT program, the experimental group showed improvements of 18% in CMJ performance, 8% in COD performance, and 25% in NHCBP performance. Conclusions: The NHCT program significantly increased hamstring muscle strength in football players, and this increase positively affected players’ linear speed and change of direction performance. NHCT has the potential to enhance athletic performance in football.

1. Introduction

Football is a complex sport involving a wide range of motor skills, including agility, balance, coordination, speed, strength, and endurance [1]. As with many other sports, speed and strength are key performance parameters in football, with a particular emphasis on the quadriceps and hamstring muscles in the lower extremities, which play a central role in these abilities [2]. Hamstring muscle activity increases significantly during acceleration and maximal sprint performance, making it essential for effective play during high-speed movements [3]. In particular, hamstring muscle strength is important for preventing injuries, shortening the rehabilitation period after injury, and enhancing athletic performance [4]. In football, the lower extremities are exposed to more stress and impact due to movements such as sudden deceleration, acceleration, short sprints, kicking the ball, and jumping [5,6], thus leading to more frequent injuries compared to the upper extremities [7,8,9]. Such injuries are believed to result from tissue damage caused by forces that exceed the mechanical limits of the tissue [10,11].

Eccentric contraction is a training method that involves various types of muscle contractions to enhance hamstring muscle strength and dissipate mechanical energy during deceleration of the body [12], thereby facilitating the conversion of kinetic energy into elastic energy in the tendons [13]. For instance, plyometric training, which involves rapid muscle stretching followed by contraction, supports explosive movements, whereas strength training with overload and isoinertial methods improves muscular strength and performance by applying variable resistance during movement [14]. Eccentric strength exercises are the most researched and recommended exercises for preventing hamstring injuries [15,16,17].

In recent years, Nordic hamstring curl training (NHCT), a type of training based on eccentric contractions aimed at increasing hamstring muscle strength and performed on flat ground without requiring special equipment, has been accepted as a popular training method [18]. Hamstring muscle activation during NHCT, which involves knee and hip joint movements, requires greater maximal eccentric muscle strength than traditional hamstring exercises [19]. The use of body weight for resistance and the fact that no special equipment is needed are the reasons for the widespread use of this exercise [20]. A literature review showed that NHCT research reports increased muscle activation, eccentric muscle strength, and jump height [21]. Many studies have shown that NHCT reduces the risk of injury, improves muscle performance, and is an important exercise that strengthens the hamstring muscles [22,23,24,25]. Contrary to some findings, other studies suggest that hamstring muscle strength may not be directly correlated with athletic performance [26,27]. In this context, the present study aimed to evaluate the effect of an 8-week NHCT program on athletic performance (linear sprint, jump, and change of direction speed) of young soccer players by increasing eccentric muscle strength. We hypothesized that the NHCT program would lead to improvements in eccentric muscle strength, jump performance, and change of direction ability, contributing positively to athletic performance.

2. Materials and Methods

2.1. Study Design and Participants

A randomized controlled trial design was used to determine the effects of the NHCT program on sprinting, COD, CMJ, and eccentric strength. The experimental approach was applied during the competition period to increase validity and applicability. Before the start of the study, an introductory visit was conducted. During this visit, the athletes were randomly divided into training (TG = 20) and control (CG = 20) groups using simple randomization, a method in which participants were assigned to groups using random number generators. After the pre-test measurements were taken to establish baseline performance data, the TG underwent an eight-week program that combined the NHCT protocol with standard football training. The CG, on the other hand, continued their regular football training without the inclusion of the NHCT program. Post-test measurements were performed at the end of eight weeks following the NHCT program.

All subjects and their parents were informed of the purpose of the study, the Declaration of Helsinki was adhered to, and informed consent was obtained. Parental permission was obtained, and informed consent was obtained from all the subjects. The study was approved by the ethics committee of the Çukurova University Faculty of Medicine (decision number 05.04.2024/143-76).

Forty male football players, who were active competitors in the U17 category, participated in this study. Football players regularly perform 4–5 weekly football training sessions with their teams. The average training duration was 8.5 ± 1.5 h/week. Since it was held during the competition period, the team regularly played an official weekly match. Athletes who had not previously participated in any eccentric training program and had no injuries were included in the study.

2.2. Procedures

This study examined the effects of the NHCT program on the athletic performance of football players. The training program was implemented with a load progression principle, with increasing sets and repetitions every two weeks [28]. The athletes were instructed to perform the movements correctly, ensuring maximum eccentric muscle contraction. They performed the exercises in pairs with similar body weights in the field, focusing on controlling the forward falling motion by using their hamstring muscles. All exercises were supervised by an athletic performance coach, with each coach overseeing five football players to ensure quality. The implementation of this movement is illustrated in Figure 1.

Pre-tests were conducted in three separate sessions at 48 h intervals. The first session included anthropometric measurements, jump performance (CMJ), and eccentric muscle strength (Nordic hamstring curl breaking point angle (NHCBP)); the second involved 10–20–30 m sprint tests; and the third focused on the change of direction (COD) test. All tests were conducted at semi-professional Adana Vefa Sports Club facilities under appropriate environmental conditions. Sprint and COD tests were performed in an international standard grass field. In contrast, other tests were conducted at sea level in the club’s athletic performance studio, with controlled temperature and humidity (mean temperature 24 °C, mean humidity 29%, and barometric pressure range 1010–1025 mmHg). To minimize circadian rhythm effects, the same researcher conducted both pre-tests and post-tests at the same time of day (17:00–18:00). Each test session included a 15 min general warm-up protocol and a four-minute passive rest before applying group-specific protocols.

2.3. Nordic Hamstring Curl Training Program

All practices were held in the training field. The exercise protocol was applied to pairs of athletes with similar weights. NHCT involves athletes kneeling, with their ankles held by a partner, slowly lowering themselves into a face-down position, and then returning to the kneeling position as slowly as possible. The player started on his knees, with his torso held straight at 90°. The training partner applied pressure to the player’s heels/lower legs, ensuring that the player’s feet remained in contact with the ground throughout the exercise. The player then attempts to resist the forward falling motion using the hamstring muscles to maximize loading in the eccentric phase. The players were asked to use their hamstrings to stop falling forward for as long as possible. Hands and arms are used to stop falling forward and push the subject back after the chest contacts the ground, thus minimizing loading during the concentric phase [19]. After movement, repetitions were continued by returning to the starting position. The entire exercise protocol was continued under the supervision of an athletic performance coach. Each athletic performance coach observed only five football players to improve the quality of the observations. An exercise protocol was implemented to increase movement quality by making the necessary corrections. The Nordic hamstring curl training program is shown in Figure 2.

2.4. Instruments

2.4.1. Weight and Height Measurement

The height (with 0.5 cm sensitivity) and weight (with 100 g sensitivity) of the athletes were measured using a Seca stadiometer. The demographic characteristics of the participants (age and age at sports) were determined using a questionnaire prepared by the researchers.

2.4.2. Counter Movement Jump (CMJ)

The CMJ test was performed using a Witty Microgate jump (Version 1.13.0, Bolzano, Italy). Athletes jumped to their highest point at the midpoint of the jump mat with their hands free. During the measurements, the jump height of the athlete was recorded. The measurements were repeated thrice, and the average height was recorded [29].

2.4.3. 10 m, 20 m and 30 m Sprint Test

The 10 m, 20 m, and 30 m sprint tests were performed using the Witty Microgate photocell system (Version 1.6, Bolzano, Italy). The Microgate photocell system was placed at 10, 20, and 30 meters. Athletes positioned themselves at the starting point, leaving 1 m behind the photocell. As soon as the athletes felt ready, they ran a 30 m distance as fast as possible. The measurements were repeated thrice, and the average values for 10, 20, and 30 m were recorded.

2.4.4. Change of Direction Test (COD)

COD test data were measured using a Witty Microgate photocell system (Version 1.6, Bolzano, Italy). The test consisted of three slaloms placed 5 m apart in a zigzag formation at an angle of 100° to each other, covering a distance of 20 m. The athletes passed the test between the 3 slaloms at the highest speed, starting 1 m behind the starting line. The test was performed thrice for each athlete, and the best score was recorded [30,31].

2.4.5. Nordic Hamstring Curl Breaking Point Angle (NHCBP)

Participants kneeled on the mat with their elbows bent and their hands open in front, while their teammates held their feet behind them steady. The athletes were instructed to slowly lean forward and maintain a straight posture from the knee to the head. The researcher ensured the correct implementation of the NHCBP. The breaking point of NHCBP movement was determined using movement analysis. In the analysis, an iPhone 14 camera was set to 240 fps and positioned approximately 3 m from the right side of the participants at a height of approximately 0.9 m. After the recorded video was transferred to a personal computer, two-dimensional motion analysis was performed using motion analysis software (KİNOVEA, Inc. [version 0.9.5]). Digitalization determines the angle from the knee to the ground when the athlete loses balance and stops moving in the NHCBP as the breaking point [32,33]. The measurements were repeated three times, and the average time was recorded.

2.5. Statistical Analysis

The dataset was primarily examined for erroneous values, outliers, and multicollinearity. The normality of the distributions was examined using the skewness and kurtosis tests. As the skewness and kurtosis coefficients were in the range of −1.5 to +1.5, the distribution was normal [34]. The SPSS 25 software package was used to analyze the data. The demographic characteristics of the athletes were analyzed using descriptive statistics. Results are presented as arithmetic mean ± standard deviation (x ± SD). Because the normal distribution assumptions were met, parametric tests were used. Repeated measures analysis of variance (ANOVA) (2 groups × 2 times) was applied to detect differences in the CMJ, COD, and NHCBP parameters at 10, 20, and 30 m. For variables with significant group–time interactions, the Bonferroni test was applied to compare group and time changes. Greenhouse–Geisser corrections were applied to F tests when Mauchly’s test of sphericity was violated.

Additionally, partial eta squares (η²) were calculated for the effect size. The effect size obtained from η² was grouped as large if ≥0.14, medium if ≥0.06, and small if <0.06 [35]. The Intraclass Correlation Coefficient (ICC) determined the reliability of the study. Thus, the ICC takes a value between 0 and 1 and is interpreted as 0.00–0.49, “poor reliability”, 0.50–0.75, “moderate reliability”, or 0.75–0.90, “good reliability”, and ICC results of 0.90–1.00 were interpreted as “excellent reliability” [36]. In this study, the statistical significance level was set at p < 0.05.

3. Results

Descriptive data on the participants’ height, body weight, body mass index (BMI), and sports age are shown in Table 1.

No group $\times$ time interaction was found in the 10 m (f = 1.94; p < 0.18; η² = 0.09), 20 m (f = 1.25; p < 0.27; η² = 0.06) and 30 m (f = 3.07; p < 0.09; η² = 0.14) performance of soccer players (p > 0.05). A statistically significant difference was found in the group $\times$ time interaction in CMJ (f = 19.99, p < 0.001, η² = 0.52), COD (f = 11.10, p < 0.004, η² = 0.38), and NHCBP (f = 6.14; p < 0.02; η² = 0.25) performance. After 8 weeks of Nordic hamstring curl exercise, the performance of the athletes in the experimental group improved by 18% for CMJ, 8% for COD, and 25% for the NHCBP. In the CG group, there was an approximate increase of 4% in CMJ, whereas the NHCBP exhibited a decrease of approximately 9%. However, these differences were not statistically significant (Table 2).

4. Discussion

This study examined the effects of the NHCT program on linear speed, change of direction, jump performance, and eccentric strength levels in young football players. After the eight-week NHCT program, the COD, CMJ, and eccentric strength levels of the football players in the training group significantly increased. In the control group, no significant improvement was observed in the athletic performance parameters.

After NHCT training, the NHCBP of the players in the training group significantly decreased. This decrease indicates that players were able to contract more eccentric muscles against gravity. Based on the applied training protocol, the training group achieved a 25% increase in eccentric muscle strength. Studies on football that included NHCT protocols with varying sets and repetitions have reported an increase in hamstring strength [4,22]. This finding is consistent with the results of our study and demonstrates the positive effect of the NHCT training program on muscles. Hamstring muscle strength is critical, as it has been shown to contribute significantly to injury risk. A previous prospective cohort study assessing the impact of hamstring muscle strength during the Nordic hamstring exercise indicated that eccentric hamstring strength is a key factor in the risk of hamstring strain injury [37]. Specifically, elongation of the biceps femoris (BF) muscle during NHCT alters the force–velocity and force–length relationships, which directly influence muscle function and mitigate muscle damage [37,38]. Moreover, an 11% increase in BF muscle length was associated with an approximately 21% reduction in the incidence of hamstring injuries [37]. These findings align with other studies highlighting the importance of enhanced eccentric hamstring strength and increased BF length in preventing hamstring injuries [28,39,40].

Football involves high-intensity actions such as sprints, changes of direction, and jumping, which require a developed neuromuscular system [41,42]. The improvement in COD and linear sprint performance observed in our study supports these findings [4,43]. Studies have reported the contribution of NHCT to athletic performance by increasing the change of direction speed in young football players [43,44,45], but Siddle et al. [45] reported that low-volume NHC exercises do not affect linear sprinting. In our study, the effect on linear sprint may be due to the gradual increase in the intensity of NHC exercises. The findings of our study are consistent with these results, underlining the contribution of NHCT to neuromuscular development and performance increase. These findings reveal the necessity of adding NHCT to training programs, especially for sports such as football, which require speed and agility.

It is known that modern football requires not only sprints and changes of direction, but also superiority in aerial balls. Success in aerial balls is directly related to the vertical jumping ability of players [46,47]. NHCT improves jump performance by increasing the power-production capacity of these muscles. For instance, it has been reported that an 8-week NHCT program led to significant improvements in CMJ and squat jump performance [48,49]. During jumping, the gastrocnemius muscle plays a critical role in producing large amounts of force and power [50]. NHCT is also thought to enhance the performance of this muscle, although further research is needed because of the limited number of studies on this subject. In this context, studies examining the positive effects of NHCT programs on jump performance more comprehensively can provide important insights for athletes to develop this critical skill.

This study has some limitations. The study was conducted with a relatively small sample size of 40 male football players in the U17 category. While this focused sample offers valuable insights, the absence of a range of performance levels (such as professional or amateur players) suggests that future studies could benefit from including a broader diversity of athletic backgrounds. This would help to better understand how the findings may be applied to other contexts, such as professional football environments or different age groups. This study focused on male participants, which may limit its applicability across genders. Including female athletes in future research could offer a more comprehensive view and enrich the understanding of these outcomes across the football-playing population. The eight-week duration of the intervention was inadequate for evaluating the long-term effects of enhancements in athletic performance. In the current study, it is essential to implement a greater frequency and extended duration of interventions to gain a comprehensive understanding of the NHCT program’s impact on injury risk. The effectiveness of such programs in injury prevention typically requires a longer timeframe to manifest. Consequently, a significant limitation of this study is its inability to make definitive claims regarding long-term benefits. The inclusion of psychological assessments could help differentiate between physical improvements due to training and those driven by mental factors. Addressing these limitations in future studies may provide more comprehensive findings.

5. Conclusions

The NHCT program, administered bi-weekly over eight weeks, demonstrated clear and significant positive effects on sprinting, change of direction speed, jumping, and eccentric muscle strength among young football players. However, this study did not sufficiently explore the applicability of these benefits to other sports contexts or age demographics. Additionally, variations that might enhance the efficacy of the NHCT program for diverse sports categories were not investigated. Consequently, it is essential to assess whether these findings can be replicated across different sports environments and demographic groups. While the practical nature and straightforward implementation of NHCT provide considerable advantages for coaches and athletes, further research is imperative to comprehensively evaluate the program’s potential across various athletic populations. Thus, athletes and coaches should familiarize themselves with NHCT and incorporate this training regimen into their training strategies, while underscoring the necessity for broader validation of the program.

Author Contributions

Conceptualization, N.S.A., M.K., B.Ö., H.E., A.K., U.C., B.E.O. and M.I.A.; data curation, N.S.A., M.K. and B.Ö.; formal analysis, N.S.A., A.K., U.C. and M.I.A.; methodology, N.S.A., M.K. and A.K.; writing—original draft, N.S.A., M.K., B.Ö., H.E., A.K., U.C., B.E.O. and M.I.A.; writing—review and editing, N.S.A., M.K., B.Ö., H.E., A.K., U.C., B.E.O. and M.I.A. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

This study was conducted in accordance with the Declaration of Helsinki and was reviewed and approved by the ethics committee of Çukurova University’s Faculty of Medicine with the decision number 05.04.2024/143-76 (Dated: 5 April 2024).

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

Data are available for research purposes from the corresponding author upon reasonable request.

Acknowledgments

We would like to thank Princess Nourah bint Abdulrahman University for supporting this project through Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2024R 286), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analysis, or interpretation of the data; in the writing of the manuscript; or in the decision to publish the results.

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figures and Tables

Table 1

Demographic characteristics.

Variables	TG (n = 20)	CG (n = 20)	Total
Height (cm)	1.76 ± 0.03	1.78 ± 0.06	1.77 ± 0.05
Body Mass (kg)	66.50 ± 5.66	68.10 ± 11.33	67.30 ± 8.76
BMI (kg/m2)	21.41 ± 1.21	21.25 ± 2.09	5.25 ± 1.41
Sport Age (year)	4.90 ± 1.28	5.60 ± 1.50	21.33 ± 1.66

Table 2

Effects of Nordic hamstring curl exercise on sprint, COD, CMJ, and NHCBP.

	TG (n = 20)		CG (n = 20)		ANOVA-p
	Pre-Test$\overline{\mathit{x}}$ ± SSICC (95%)	Post Test$\overline{\mathit{x}}$ ± SSICC (95%)	Pre-Test$\overline{\mathit{x}}$ ± SSICC (95%)	Post Test$\overline{\mathit{x}}$ ± SSICC (95%)	$\mathbf{Group}\times \mathbf{Time\; Interaction}$
					F	p	ηp2
CMJ (cm)	33.37 ± 2.120.811 (%)	39.50 ± 1.500.952 (%)	31.93 ± 2.060.838 (%)	33.19 ± 1.680.925 (%)	19.993	<0.001 ♦†	0.526
	p < 0.001		p = 0.121
10 m (s)	1.76 ± 0.070.845 (%)	1.69 ± 0.060.904 (%)	1.76 ± 0.070.905 (%)	1.76 ± 0.070.940 (%)	1.944	0.180	0.097
	p = 0.047		p = 0.871
20 m (s)	3.01 ± 0.082.909 (%)	2.92 ± 0.080.933 (%)	3.01 ± 0.120.928 (%)	2.99 ± 0.170.984 (%)	1.259	0.277	0.065
	p = 0.050		p = 0.613
30 m (s)	4.25 ± 0.230.950 (%)	4.12 ± 0.290.983 (%)	4.31 ± 0.250.984 (%)	4.32 ± 0.230.975 (%)	3.075	0.097	0.146
	p = 0.032		p = 0.874
COD (s)	5.69 ± 0.470.986 (%)	5.25 ± 0.180.977 (%)	5.38 ± 0.360.938 (%)	5.42 ± 0.230.989 (%)	11.108	0.004 ♦†	0.382
	p < 0.001		p = 0.732
NHCBP	51.61 ± 7.600.874 (%)	38.95 ± 7.880.948 (%)	52.11 ± 7.340.871 (%)	47.81 ± 7.450.837 (%)	6.146	0.023 ♦†	0.255
	p < 0.001		p = 0.088

CMJ: Counter Movement Jump; COD: Change of Direction; NHCBP: Nordic Hamstring Curl Breaking Point Angle. ^♦ denotes a significant difference (p < 0.05) compared with the pre-test results. ^† denotes a significant difference (p < 0.05) compared with the CON group.

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