Abstract
his study aimed to examine the relationships between isometric mid-thigh pull maximal force (IMTPF), sprint mechanics, and performance. Fifteen national-level track and field athletes (sprinters and hurdlers) performed three maximal-effort isometric mid-thigh pulls on a force plate and two 30 m sprints. The IMTPF, the sprint mechanical variables (theoretical maximum horizontal force (F0), velocity (v0), and power (Pmax)), as well as the sprint performance data at 5 m distance intervals, were collected. Pearson’s product–moment correlation analysis revealed large linear associations between IMTPF and v0(r = 0.65, R 2 = 0.42,p= 0.009), as well as negative linear relationships between IMTPF and sprint times of 15 m (r =−0.53, R 2 = 0.28,p= 0.043), 20 m (r =−0.55, R 2 = 0.30, p= 0.033), 25 m (r =−0.57, R 2 = 0.33,p= 0.025), and 30 m (r =−0.60, R 2 = 0.36,p= 0.019). The F0, Pmax, and sprint times to 5 m and 10 m were not significantly correlated with the IMTPF (p< 0.05). The study results highlight that during the late acceleration phase (>15 m), the capacity to generate horizontal force at high running velocities is related to the ability to develop maximal force during isometric contractions. Keywords:sprint mechanics; isometric force;
0.019). The F0, Pmax, and sprint times to 5 m and 10 m were not significantly correlated with the IMTPF (p< 0.05). The study results highlight that during the late acceleration phase (>15 m), the capacity to generate horizontal force at high running velocities is related to the ability to develop maximal force during isometric contractions. Keywords:sprint mechanics; isometric force; sprint performance; mid-thigh pull 1. Introduction Sprinting is a maximal speed cyclic locomotion mode and is a critical physical fac- tor of performance in many individual and team sports. Sprinting performance can be divided into three primary phases, as follows: acceleration, maximum velocity and deceler- ation [1]. A successful acceleration phase is dependent on the ability to generate and apply high horizontally oriented forces into the ground, during the support phase, at various velocities [2]. The acceleration phase can in turn be segregated into early, middle, and late subsections [3,4]. The early acceleration phase corresponds to 1–3 steps, the middle phase to 5–15 steps, and the late phase to 16–28 steps, based on the average height of the athletes’ center of gravity during the support phase of the step cycle [3]. The early phase is mechanically characterized by long contact times, enabling the generation of a high level of horizontal force applied at low running velocity. The middle phase, or transition phase, is characterized by a reduction in contact times, resulting in a notable decrease in horizontal force production. The late acceleration phase is characterized by shorter contact times, compared to the previous phases, enabling the production of a lower level of horizontal force applied at a considerably higher running velocity [2]. It is known that during the Appl. Sci.2025,15, 1089 https://doi.org/10.3390/app15031089
Appl. Sci.2025,15, 1089 2 of 11 acceleration phase, an athlete’s expression of strength demonstrates notable variations. For instance, lower limb power assessed through squat jumps and countermovement jumps exhibits a significant association with the early acceleration phase. In contrast, reactive strength evaluated via repeated ankle jumps shows a significant correlation with the late acceleration phase [5]. The overall capacity to generate horizontal force during sprint acceleration motion is effectively characterized by the sprint mechanical profile [6,7], which has been widely used to identify the mechanical capabilities of the neuromuscular system that underpins sprint acceleration performance [8–11]. The variables that define the sprint mechanical profile include the theoretical maximum horizontal force (F0), which represents the initial push exerted by the athlete onto the ground during sprint acceleration; the theoretical maximum horizontal velocity (v0), which denotes the maximum velocity the athlete could theoretically achieve if mechanical resistances to movement were absent, and also reflects the ability to produce horizontal force at high running velocities; and the theoretical maximum horizontal power (Pmax), which represents the peak combination of force and velocity attained during sprint acceleration [12]. A sprinter’s maximal force production and capacity to rapidly express forces are essential factors contributing to their efficiency in the acceleration phases [13]. Multi-joint isometric assessments such as the isometric mid-thigh pull (IMTP) are commonly used to evaluate the maximum force produced and the force–time capabilities of athletes [14]. Peak force is the most common and reliable measure obtained during IMTP [15], as it reflects maximal strength during an isometric voluntary contraction [16]. The maximum force produced by the lower limbs occurs after 300 ms [17]. Several studies have examined the relationship between IMTP peak force (IMTPF) and sprinting performance. Specifically, Mason et al. [18] showed a large association between IMTPF and the maximum running velocity phase (r = 0.57) in professional soccer players. Additionally, Thomas et al. [19] found a strong negative relationship between IMTPF and sprint times of 5 m (r =−0.57) and 20 m (r =−0.69) in male collegiate soccer and rugby athletes. In addition, Townsend et al. [20] found a strong negative correlation
large association between IMTPF and the maximum running velocity phase (r = 0.57) in professional soccer players. Additionally, Thomas et al. [19] found a strong negative relationship between IMTPF and sprint times of 5 m (r =−0.57) and 20 m (r =−0.69) in male collegiate soccer and rugby athletes. In addition, Townsend et al. [20] found a strong negative correlation between IMTPF and 0–5 m, 0–10 m, 0–15 m, and 0–20 m sprint acceleration performances (r =−0.62, r =−0.67, r =−0.70, r =−0.69, respectively) in professional male and female basketball players. Moreover, Brady et al. [15] found large negative associations between IMTPF and 0–5 m, 10–20 m, and 0–30 m sprint performances (r =−0.63, r =−0.53, r =−0.60, correspondingly) in high-level male sprinters. On the other hand, West et al. [21] reported no significant relationships between IMTPF and sprinting performance in collegiate rugby league players. In contrast, authors observed a weak inverse relationship (r =−0.37) between IMTPF normalized to body mass with 10 m sprint time. Similarly, Scanlan et al. [22] reported moderate correlations between IMTP normalized peak force and 5 m (r =−0.44) and 10 m sprint time (r =−0.45) in male adolescent basketball players. Furthermore, Wang et al. [23] observed no significant correlations between IMTPF and sprint times of 5 m and 10 m in collegiate rugby union players. Finally, another study indicated a lack of correlations between IMTPF and sprint acceleration performance from 0 to 40 m-distance intervals in national- and international- level sprinters [24]. The observed differences in the relationships between IMTPF and acceleration performance may be attributed to the fact that the IMTP primarily assesses the ability to generate force in the vertical direction. However, this may have limited relevance for team sport athletes, who are trained to execute movements in the horizontal, frontal, and transverse planes. Additionally, variations in factors such as contact time, running distance, running posture, surface type, and footwear may also contribute to these differences. In contrast with the availability of studies documenting the relationships between isometric strength and sprinting performance, few have investigated their relationships with sprint mechanical properties. Townsend
are trained to execute movements in the horizontal, frontal, and transverse planes. Additionally, variations in factors such as contact time, running distance, running posture, surface type, and footwear may also contribute to these differences. In contrast with the availability of studies documenting the relationships between isometric strength and sprinting performance, few have investigated their relationships with sprint mechanical properties. Townsend et al. [20] found large relationships between
Appl. Sci.2025,15, 1089 3 of 11 IMTPF and average values of force, velocity, and power from 5 to 20 m of sprinting performance (r = 0.48–0.69, 0.50–0.70, and 0.62–0.73, respectively) in basketball players. Moreover, Healy et al. [24] reported a significant relationship between IMTPF and Pmax (r = 0.61) in male sprinters. Nevertheless, the authors indicated an absence of correlation between maximal strength assessments and sprint mechanical characteristics in female sprinters. It remains uncertain whether the ability of elite sprinters to generate and apply horizontal force and power during the specific phases of sprint acceleration is linked to their ability to produce isometric maximal force, as evaluated by the IMTP. Further observations are warranted to define the relationship of IMTPF assessments in the specific acceleration phases with their underlying mechanical variables. In particular, incorporating mechanical characteristics into the analysis of sprint performance could provide valuable insights for coaches and practitioners, enhancing their understanding of the lower limbs’ maximal force capacities and their relevance to sprint acceleration phases. Therefore, this study aimed to examine the relationships between IMTPF, sprint acceleration performance, and its underpinning mechanical properties in national-level track and field athletes during the competitive period of the season. It was hypothesized that the IMTPF would be related to the sprint acceleration performance and its underpinning mechanical properties. 2. Materials and Methods 2.1. Participants Fifteen national-level track and field athletes, eight males (mean±standard deviation (SD): age 26.0±3.4 years; weight 73.2±5.4 kg; stature 1.80±0.06 m) and seven females (age 23.0±3.4 years; weight 59.5±8.4 kg; stature 1.68±0.10 m), volunteered for the present study. The participants were briefed on the study protocol before providing written consent. The protocol was approved by the institution’s Research Ethics Committee, in alignment with the Declaration of Helsinki II. Among the males were four 100 m sprinters, two 200 m sprinters, one 400 m sprinter, and one 110 m hurdler. Among the females, there were five 100 m sprinters and two 100 m hurdlers. All participants were free of physical limitations and musculoskeletal injuries that could compromise testing. Participants were asked to refrain from resistance training at least 24
Among the males were four 100 m sprinters, two 200 m sprinters, one 400 m sprinter, and one 110 m hurdler. Among the females, there were five 100 m sprinters and two 100 m hurdlers. All participants were free of physical limitations and musculoskeletal injuries that could compromise testing. Participants were asked to refrain from resistance training at least 24 h before testing procedures. The testing facilities were maintained under consistent environmental conditions, specifically a temperature of 25 ◦ C and a humidity level of 52%. 2.2. Procedures Participants were involved in two separate testing sessions within the same week. During these sessions, anthropometric measurements, including stature and body mass, were measured. The first session involved the assessment of IMTPF, while 30 m sprint measures were completed in the second session. Before the first testing session, participants visited the laboratory to gain familiarization with the IMTPF assessment protocol. 2.3. Isometric Mid-Thigh Pull Participants completed a general warm-up, consisting of 3 min of cycling and 10 repe- titions of squats, lunges, and glute-bridges. Subsequently, an isometric-specific warm-up was conducted, comprising a 5 s of IMTP bout at a self-directed position at 50%, a 3 s bout at 75%, and a 3 s bout at 90% of maximal effort with 1 min rest between each bout [15]. After the warm-up, participants performed 3 maximal-effort isometric pulls separated by 3 min of recovery. The IMTP was performed with a custom-designed power rack that allows fixation of the steel bar height, with the participants standing on an 80×80 cm force plate (WP800, Applied Measurements Ltd. Co., Aldermaston, UK, operating at 1000 Hz). At the
Appl. Sci.2025,15, 1089 4 of 11 start of each trial, participants were positioned in the second-pull phase of the clean, with knee angles set at 141 ◦ ± 4 ◦ and hip angles set at 138 ◦ ± 2 ◦ [15]. These angles were verified prior to each trial using a hand-held goniometer. To standardize grip strength, participants utilized lifting straps, and both grip width and foot positioning were standardized across participants [25]. Participants were instructed to maintain a low, steady baseline force at the beginning of each trial in order to avoid precontraction [16] and then directed to exert maximal pulling force for a period of 4 s, initiated by a countdown of “3, 2, 1, Go!” [14]. The duration of the collection period for each trial was established at 12 s, with a baseline measurement obtained during the 3 s countdown preceding the initiation of the pull [15]. Verbal encouragement was provided during each trial. Data from the force plate were collected at a sampling rate of 1000 Hz (Kyowa sensor interface PCD-320A, Chofu, Japan). The signal was then processed using a fourth-order, zero-lag Butterworth low-pass digital filter with a cutoff frequency of 20 Hz. From the force-time data, the highest force value achieved during the 4 s best trial, minus the participant’s body weight in Newtons, was reported as the IMTPF. The contraction onset threshold was established based on five Standard Deviations (SD) above participant’s body weight [26]. The reliability of the IMTP test to measure the maximal force has been examined previously and provided a very high intraclass correlation coefficient (ICC) (ranging from 0.92 to 0.99 with coefficients of variation (CV) >5%) [27]. 2.4. 30 m Sprint Test After their usual warm-up routine, lasting ~30 min, participants performed 2 maximal linear 30 m sprints from a three-point starting position on an indoor track, with a 5 min recovery period between sprints. The temporal data for each sprint were collected using a high-speed camera (Casio EX-F1, Tokyo, Japan, operating at a frequency of 300 Hz). The high-speed camera was mounted on a tripod, positioned perpendicular to the
participants performed 2 maximal linear 30 m sprints from a three-point starting position on an indoor track, with a 5 min recovery period between sprints. The temporal data for each sprint were collected using a high-speed camera (Casio EX-F1, Tokyo, Japan, operating at a frequency of 300 Hz). The high-speed camera was mounted on a tripod, positioned perpendicular to the direction of running, and located 10 m from the runway at the midpoint of the sprinting distance (i.e., 15 m). Six poles were positioned at intervals along the 30 m distance to delineate the 5 m split times. The poles were placed at adjusted positions to correct video parallax errors [28]. The onset of the sprint was delineated as the initial propulsive movement of the rear leg emerging from the three-point starting position [29]. The sprint spatiotemporal characteristics in intervals of 5 m were determined from the modeled velocity–time data using Quintic Biomechanics software v31 (Quintic Consultancy Ltd., Birmingham, UK) [30]. The variables of the sprint mechanical profile were determined according to Samozino’s method [6,7]. The Samozino method represents a macroscopic biomechanical model validated for estimating the external horizontal force produced during sprinting. This estimation is achieved by employing an inverse dynamic approach that utilizes the velocity of the center of mass. Specifically, a mono-exponential function is applied to the raw velocity–time data through a custom spreadsheet, wherein a least-squares regression fitting procedure is implemented. This methodology facilitates the calculation of the athlete’s center-of-mass acceleration in the horizontal direction by analyzing the changes in running speed over time. Furthermore, the net horizontal anteroposterior ground reaction forces are assessed by considering the athlete’s body mass and the effects of aerodynamic friction. The theorical maximal horizontal force and velocity (F0and v0) were extrapolated from the linear force (F) and (v) relationship by determining the intercepts on the F and v axes, respectively, from the linear regressions. By multiplying the horizontal F and v values for each support phase, the Pmax, normalized to body mass, in the forward direction is derived. It is calculated using the formula Pmax= F0.v0 4 [6,7].
extrapolated from the linear force (F) and (v) relationship by determining the intercepts on the F and v axes, respectively, from the linear regressions. By multiplying the horizontal F and v values for each support phase, the Pmax, normalized to body mass, in the forward direction is derived. It is calculated using the formula Pmax= F0.v0 4 [6,7].
Appl. Sci.2025,15, 1089 5 of 11 2.5. Statistical Analysis Data are expressed as means±SD. The normality of distribution (Shapiro–Wilks test and Q–Q plot analysis) was checked before analyses. The best trial based on IMTPF and 30 m sprint time was selected for analysis. Relationships between IMTPF, sprint acceleration performance (time to 5 m, 10 m, 15 m, 20 m, 25 m, and 30 m) and underlying mechanical properties (F0, v0, and Pmax) were analyzed using Pearson product–moment correlation coefficients (r), which were conducted through SPSS software (version 28.0, IBM Corp., Armonk, NY, USA). To assess the relative strength of the relationship, the scale modified by Hopkins et al. [31] was used—trivial (<0.1), small (r = 0.1–0.3), moderate (0.3–0.49), large (0.5–0.69), very large (0.7–0.89) and nearly perfect (>0.9). The criterion for statistical significance was considered asp≤0.05. 3. Results Descriptive statistics and qualitative interpretations of the Pearson’s correlation be- tween IMTP assessment, sprint mechanical variables, and performance are presented in Table. The intraclass correlation coefficient (ICC) between IMTPF and 30 m sprinting performance trials was very high (0.97 and 0.99, respectively). Table 1.Means±SD, 95% Confidence Intervals (CI), Pearson’s correlations, and qualitative interpre- tations of the Pearson’s correlation coefficients of IMTP assessment, sprint mechanical profile, and sprint acceleration performance variables. Variables Mean (SD) 95% CI Relationship with IMTPF (r) ES IMTPF (N) 2366 ±511 2082–2648 F0(N·kg −1 ) 7.50±0.95 6.98–8.02 0.20 ( −0.35 to 0.65) Small v0(m·s −1 ) 10.13±0.66 9.76–10.50 0.65 ** (0.21 to 0.87) Large Pmax(W·kg −1 ) 19.02±2.90 17.41–20.62 0.44 ( −0.09 to 0.78) Moderate Time to 5 m (s) 1.30 ±0.08 1.25–1.34 −0.38 (−0.74 to 0.17) Moderate Time to 10 m (s) 2.00 ±0.10 1.94–2.06 −0.50 (−0.81 to 0.01) Large Time to 15 m (s) 2.62 ±0.13 2.55–2.69 −0.53 * (−0.82 to −0.21) Large Time to 20 m (s) 3.20 ±0.16 3.11–3.28 −0.55 * (−0.83 to −0.06) Large Time to 25 m (s) 3.75 ±0.18 3.65–3.85 −0.57 * (−0.84 to −0.09) Large Time to 30 m (s) 4.29 ±0.21 4.18–4.41 −0.60 * (−0.85 to −0.12) Large IMTPF = isometric mid-thigh pull peak force; 95% CI = 95% confidence intervals;
* (−0.82 to −0.21) Large Time to 20 m (s) 3.20 ±0.16 3.11–3.28 −0.55 * (−0.83 to −0.06) Large Time to 25 m (s) 3.75 ±0.18 3.65–3.85 −0.57 * (−0.84 to −0.09) Large Time to 30 m (s) 4.29 ±0.21 4.18–4.41 −0.60 * (−0.85 to −0.12) Large IMTPF = isometric mid-thigh pull peak force; 95% CI = 95% confidence intervals; ES = effect size; r = Pearson’s correlation coefficients; F0= theoretical maximal horizontal force; v0= theoretical maximal horizontal velocity; Pmax= theoretical maximal horizontal power. * =p≤0.05; ** =p≤0.01. Pearson’s product-moment correlation analysis revealed large linear associations between IMTPF and v0(r = 0.65, R 2 = 0.42,p= 0.009) (Figure). In addition, IMTPF demonstrated large negative linear relationships with sprint times to 15 m (r =−0.53, R 2 = 0.28,p= 0.043), 20 m (r =−0.55, R 2 = 0.30,p= 0.033), 25 m (r =−0.57, R 2 = 0.33, p= 0.025), and 30 m (r =−0.60, R 2 = 0.36,p= 0.036) (Figure). The F 0, Pmax, and sprint times to 5 m and 10 m were not significantly related to IMTPF (r = 0.20, R 2 = 0.04,p= 0.474; r = 0.44, R 2 = 0.19,p= 0.102; r =−0.38, R 2 = 0.14,p= 0.169; r =−0.50, R 2 = 0.25,p= 0.057, respectively). However, a trend of relationship between IMTPF and time to 10 m (r =−0.50, p= 0.057) was noted.
Description
The study explores the relationship between IMTPF and sprint performance in national-level athletes.