Influence of Feet Position and Execution Velocity on Muscle Activation and Kinematic Parameters During the Inclined Leg Press Exercise

Abstract

Background:

The leg press is one of the most typical exercises for strengthening the lower limbs. The objectives of this study were to compare 5 inclined leg press exercise conditions, varying the feet width stance (100% or 150% hip width), the feet rotation (0° or 45° external rotation) on the footplate and using 2 different movement velocities (MVs; maximum intended, and 2:2 seconds steady-paced velocities) to determine their effect on muscle activation as well as on the kinematic parameters between trained men and trained women.

Hypotheses:

There will be no significant differences in muscle activation with regard to the feet position. The higher the MV, the greater the muscle activation.

Study Design:

A cross-sectional cohort study.

Level of Evidence:

Level 3.

Methods:

A repeated-measures between-group design was performed to examine muscle activation and kinematic parameters for the different conditions between gender groups. The level of significance was set at alpha = 0.05 for all statistical analyses.

Results:

Muscle activation presented no differences between conditions regarding feet width stance or feet rotation. Furthermore, muscle activation was greater during positive phases than negative phases of the exercise for all conditions and was also greater under maximum intended velocity conditions compared with steady-paced conditions. Otherwise, the muscle activation pattern presented slight differences by gender. In men, the greatest muscle activation was for the vastus medialis, followed by the vastus lateralis (VL), rectus femoris (RF), and gluteus medialis (GMED), while in women, the greatest muscle activation was for the vastus medialis, followed by the RF, VL, and GMED. Finally, greater mean propulsive velocity, maximum velocity, maximum power, and footplate displacement values were reported for men than for women under all the conditions.

Conclusion:

The inclined leg press exercise produces the highest muscle activation in the vastus medialis, regardless of the velocity, feet stance, or gender.

Clinical Relevance:

Given that there are no differences in muscle activation regarding the feet stance, a participant’s preferred feet stance should be encouraged during the inclined leg press exercise. Furthermore, the MV would preferably depend on the session objective (a training or a rehabilitation program), being aware that there is greater muscle activation at higher speeds. The inclined leg press exercise could be performed as a closed kinetic chain exercise when the main objective is to activate the vastus medialis.

The leg press is a typical exercise for lower limb strengthening.^21,45,50 The widespread applicability offered by this exercise is explained by the simplicity of its technique since it is a guided movement, ⁸ along with its transference to functional movements such as walking, squatting, running, or jumping.^6,8,13,17 This means that the exercise can be included in any training program regardless of the participants’ age^10,19,32 or training goal, whether it be for rehabilitation,^2,6,8,43 injury prevention and return to play,^17,26 health,^2,52 or athletic performance.^13,17

Given the leg press exercise’s versatility, it is essential that trainers and athletes understand the muscle activation elicited during its use, as a key factor in the concomitant development of muscle mass and strength.^31,38,45 Surface electromyography (sEMG) has been widely used in research ⁵ as a noninvasive method for assessing muscle activation and neuromuscular function.^6,11,17 This has resulted in studies assessing the muscle activation during the horizontal leg press,^{16-18,46,50,52} unilateral leg press, ⁶ and inclined leg press.^11,26 The muscles most frequently assessed using sEMG during the leg press exercise are the vastus medialis oblique (VMO), vastus lateralis (VL), rectus femoris (RF), and biceps femoris.^{13,26,28,50,52}

In addition, some other studies have evaluated the leg press exercise using different feet stances (conditions) over the footplate. For instance, a low feet position over the footplate resulted in greater quadriceps muscle activation, ¹¹ whereas there were no differences in overall muscle activation between the 30° forefoot external rotation condition and wide and narrow feet stances. ¹³ Nonetheless, the effect that these conditions may trigger on muscle activation at different movement velocities (MVs) has not yet been clearly identified.^11,13,26 On the other hand, some authors reported differences in neuromuscular function, lower body biomechanics, and kinematic responses between genders when performing dynamic tasks such as changes in direction, box jumps, and side-step cuts.^19,20,51

Kinematic parameters, which have been extensively studied in exercises such as the squat,^42,44,48 play a role in performance. Recent studies have reported similar neural ³⁶ and power adaptations after a velocity-based training program compared with a steady-paced velocity training program, protecting the athlete from unnecessary mechanical stress or fatigue.^3,15,41 However, few studies have assessed the leg press exercise at different MVs. The leg press force-velocity relationship has been studied in the older adult population, reporting that a fall in maximum power (P_max) might somehow explain the loss of physical function in the elderly. ¹ Conversely, in a population of sportsmen, the leg press presented its greatest P_max at lower velocities than in the squat. ⁴⁰ Other studies used MV to estimate relative load as a % 1 repetition maximum (% 1RM) in older women, ²⁷ whereas mean propulsive velocity (MPV) has been proposed as a better estimator of the % 1RM in young athletes performing the leg press exercise. ⁹ Therefore, displacement and task times are essential data for the accuracy of all these measurements. ²⁵ Despite this fact, knowledge regarding leg press kinematic parameters and their practical application in the healthy, young trained population remains scarce. ⁹

To the best of our knowledge, there is no current evidence comparing muscle activation and kinematic parameters between men and women while employing different feet stances and movement velocities in the inclined leg press exercise. For this reason, the objectives of the present study were (1) to compare muscle activation of the VMO, VL, RF, and gluteus medialis (GMED) between men and women under different feet stance (100% hip width and 0°/45° external feet rotation) and MV (steady-paced and maximum intended) conditions; (2) to compare the muscle activation positive phase ³⁹ under steady-paced velocity conditions (100%/150% hip combined with 0°/45° external feet rotation) between men and women; and (3) to compare kinematic parameters (MPV, V_max, P_max, footplate displacement, and time) between men and women under the different conditions.

Methods

Participants

A total of 28 healthy young college students (15 men and 13 women) volunteered to take part in the study. Table 1 shows the participants’ descriptive characteristics. Following were the inclusion criteria: (1) no health problems, musculoskeletal injuries, or physical limitations during the 6 months before the assessment; (2) at least 1 year of resistance training experience; (3) familiarity with the inclined leg press exercise; and (4) engaging in resistance training at least twice a week. In addition, the participants had to report no previous fatigue on the day of testing. The taking of any medication, drugs, or anabolic steroids was cause for exclusion from the study. The study protocol was approved by a Research Ethics Committee of the University of Almería, according to the Declaration of Helsinki. Participants signed an informed consent form before the day of testing.

Table 1.

Descriptive characteristics of the sample ^a

	Male (n = 15)	Female (n = 13)
Age, y	22.73 ± 2.93	22.77 ± 2.77
Height, cm	180.00 ± 3.68	169.54 ± 10.63
Body weight, kg	73.80 ± 16.48	61.08 ± 8.21
Hip width, cm	30.67 ± 2.05	28.38 ± 2.21
1RM, kg	257.33 ± 44.55	178.85 ± 18.27
RT experience, y	3.06 ± 1.79	3.07 ± 1.93

1RM, 1 repetition maximum; RT, resistance training.

^aData presented as mean ± SD.

Procedures

All the participants were prevented from exercising for at least 48 hours before testing to avoid fatigue bias. The protocol comprised a familiarization session and a testing session. Before the testing session, the participant’s skin was prepared by shaving the hair from the areas where the electrodes would be placed. All the inclined leg press conditions were performed during the same testing appointment to ensure the electrodes were properly placed over the muscle belly.

Before the testing, the participants performed the same previously designed warm-up protocol. First, the participants ran for 5 minutes on a treadmill (SALTER RS-30, Salter SA) at an intensity of around 40% of their heart rate reserve, followed by a dynamic warm-up comprising free weight lunges and squats.^7,12 After that, they performed 6 repetitions of the leg press exercise with light loads (<60 kg). ⁹ Then, their skin was cleaned with a 96% alcohol solution applied with cottonwool and the electrodes were placed over the VMO, VL, RF, and GMED muscles on the right limb, along with an electrogoniometer over the right knee joint, in accordance with the Surface Electromyography for the Non-invasive Assessment of Muscles guidelines.^17,18,50,52

Each testing session was supervised by a certified strength and conditioning specialist to ensure proper technique application. Before data collection, the participants were fully informed of the procedures, and the testing sessions were performed under the same environmental conditions for all the participants. Once the electrodes and electrogoniometer were positioned, the participants were briefly reminded of how to perform the technique for the conditions under study. Full knee extension was set as 0° and participants were then asked to flex their knees in a controlled manner until reaching 90° of knee flexion (or the shinbone parallel to the floor). Adhesive tape was located on the inclined leg press device at this lowest position to ensure the same range of motion for all the conditions. The feet were located at the medium height position over the inclined leg press footplate.

At this point, a linear transducer was set parallel to the inclined press device over an inclined platform. The linear transducer cable was attached to the inclined leg press bar. The inclined platform allowed one to adjust the cable inclination, so it followed the same track as the inclined leg press. For the maximal intended velocity sets, the negative phase was performed at a controlled self-selected pace, followed by a pause of 1 to 2 seconds in the 90° knee flexion position to eliminate the contribution of elastic energy accumulation.^9,27 Then, the participants were encouraged to extend their knees explosively as fast as possible. For the 2 seconds negative phase/2 seconds positive phase sets, a metronome was set at 60 beats per minute (bpm), and repetitions were performed in a continuous manner through the same range of motion.

Approach to 1RM

A load progression was carried out, with as many as 8 increments up to maximal intended velocity. As in previous studies, an increment of ~10% 1RM was added to each consecutive set until participants achieved a MPV of 0.5 m/s.^9,49 After that, the increments ranged from 5 to 1.25 kg (Azafit Bumper Plates) until 1RM was reached.

The first load was 80 kg for men and 60 kg for women. At these loads, 4 repetitions were performed at a velocity of up to 1.15 m/s MPV with a 3- to 4-minute rest between sets. Two repetitions were performed at medium loads (1.15 m/s ≥ MPV ≥ 0.5 m/s) with a 5-minute rest between them, and only 1 repetition was performed at maximum loads with a 6-minute rest (MPV < 0.5 m/s). The participants received real-time velocity feedback and verbal encouragement was provided by the examiners to ensure maximum effort.

Output Variables

Muscle activation (sEMG) was the main output variable. In addition, certain kinematic parameters (MPV, V_max, P_max, footplate displacement, and time) were assessed. Five inclined leg press conditions were randomly assessed for each participant:

At maximal intended velocity

• (a) Leg press at a stance of 100% hip-width distance and 0° of forefoot external rotation.

• (b) Leg press at a stance of 100% hip-width distance and 45° of forefoot external rotation.

At a steady-paced velocity of 2 seconds negative phase/2 seconds positive phase

• (c) Leg press at a stance of 100% hip-width distance and 0° of forefoot external rotation (0° 100%).

• (d) Leg press at a stance of 100% hip-width distance and 45° of forefoot external rotation (45° 100%).

• (e) Leg press at a stance of 150% hip-width distance and 0° of forefoot external rotation (0° 150%).

The conditions were performed at an intensity of 70% 1RM.^14,16,24 Six repetitions of each condition were performed with a 5-minute rest between sets. The sEMG data were recorded during the 1RM test and during all 5 inclined leg press sets. Furthermore, MV and knee flexion angle were monitored during the whole process by means of the linear transducer and the electrogoniometer, respectively. Although feet rotation would evidently entail subtle modifications in the knee joint position, only knee movement on the sagittal plane was considered, as movements on any other plane were inappreciable to the naked eye.

Data on the maximum voluntary activation of the targeted muscles were collected during the 1RM measurement since dynamic assessment of muscle effort has been established as a better predictor of the highest muscle activation.^7,8 Peak activation (µV) recorded at 1-second interval windows and the highest sEMG activity level at a 100-ms interval were used to obtain the maximum voluntary contraction (MVC) of each muscle to normalize the sEMG signal.^4,33,34 The sEMG muscle activation of the MVC showed an intraclass correlation coefficient (ICC) greater than 0.9, demonstrating high reliability in all the MVCs evaluated.

Instrumentation

An inclined leg press device (FITTECH PL688, Viseu, Portugal) was used for the measurements. Bipolar adhesive Ag/AgCl electrodes (Medico Lead-Lok) were placed parallel to the muscle fibers at 2-cm intervals with the reference electrode far from the electrode pairing in accordance with the manufacturer’s specifications. When necessary, the electrodes were covered with tape or a bandage to prevent possible displacement during the test.

The sEMG signal for the targeted muscles was recorded using a WBA Mega device (Mega Electronics Ltd) at a sampling frequency of 1000 Hz. The analog signal was converted to digital via an analog-to-digital converter (National Instruments) and filtered by bandwidth (12-450 Hz) with a fourth-order Butterworth filter using the LabView software program (National Instruments). Then, the raw sEMG signals were converted into root-mean-square signals for further analysis with the MEGAWIN software program (Mega Electronics Ltd). To identify the different repetitions and exercise phases in the sEMG signal analysis, the angle of the right knee was continuously recorded with an electrogoniometer (Biometrics Ltd) placed on the lateral side of the femur and the fibula. The data from the electrogoniometer were synchronized with the sEMG data using the sEMG equipment (Mega Electronics Ltd).

The footplate velocity was measured using a linear transducer (T-Force System, Ergotech) sampling at 1000 Hz and smoothed using a fourth-order low-pass Butterworth filter with no phase shift, and a 10 Hz cutoff frequency. ³² The T-Force system was connected to a personal computer where the relevant kinetic and kinematic parameters were calculated automatically for each inclined leg press repetition and for the 1RM test. T-Force software also provided real-time feedback for the participants and all data storage. The reliability of this system has been reported elsewhere. ⁴⁸ Furthermore, for the 2-second negative phase/2-second positive phase sets, a KORG MA-1 (Keio Electronic Laboratories) metronome was set at a rate of 60 bpm to control the timing of the exercises.

Statistical Analyses

The normal data distribution was analyzed using the Shapiro-Wilk normality test. Since all the variables presented a normal distribution, parametric tests were performed. The mean values and standard deviations of the dependent variables were extracted from the descriptive statistics. The 1-way random effects model was used to obtain the relative reliability of the movement with the ICC at a 95% CI.

SEMG

A 2 × 2 × 2 × 4 × 2 (gender × exercise × contraction type × muscle × velocity) analysis of variance (ANOVA) was performed to determine the differences in the muscle activation (%MVC) between the 0° 100% and 45° 100% conditions according to the exercise velocity. Furthermore, a 2 × 3 × 4 (gender × exercise × muscle) ANOVA was applied to determine the differences in the muscle activation for the positive phase (%MVC) under the 3 conditions executed at a steady-paced velocity.

Kinematic Parameters

A paired sample t test was performed to determine the differences in MPV and V_max between the 0° 100% and 45° 100% conditions executed at maximum intended velocity. Moreover, 2 separated ANOVAs were employed to determine (1) the differences in P_max between the 0° 100%, 45° 100%, and 0° 150% conditions executed at steady-paced velocity (gender × exercise) and (2) the differences in P_max between the 0° 100% and 45° 100% conditions, according to the velocities (gender × exercise × velocity) for each gender. Two separated ANOVAs (gender × exercise × contraction type) were conducted to determine the differences in footplate displacement (cm) and time (seconds) between all 5 conditions for both negative and positive phases.

Additionally, Mauchly’s sphericity test was performed on all the ANOVA results. A Greenhouse-Geisser correction was employed if an assumption was violated, whereas a Bonferroni post hoc adjustment was employed when a significant main effect was observed within pairwise comparisons. A partial eta-square (η2p) was also used to calculate the effect sizes (ES) for each ANOVA, setting 0.2, 0.5, 0.8, and 1.3 as the lower thresholds for small, medium, large, and very large ES, respectively. ²⁵ The G*power 3.1 for Mac OS X software program (14) was used to calculate a priori the sample size and statistical power. The statistical power calculated post hoc was >0.9 for all the variables. IBM SPSS software (Version 26) was used to run the statistical analyses with a level of significance set at alpha = 0.05 (P < 0.05).

Results

sEMG

Figures 1 and 2 show a comparison of the negative and positive phases of muscle activation (%MVC) for the maximum intended velocity sets and the steady-paced velocity sets under the 0° 100% and 45° 100% conditions for men and women, respectively. The ANOVA (gender × exercise × contraction type × muscle × velocity) results showed a significant main effect/interaction for contraction type (F_{(1, 26)} = 427.93, P < 0.001, η2p = 0.94), muscle (F_{(3, 78)} = 70.84, P < 0.001, η2p = 0.73), velocity (F_{(1, 26)} = 203.78, P < 0.001, η2p = 0.88), exercise × muscle (F_{(3, 78)} = 10.93, P < 0.001, η2p = 0.29), exercise × contraction type × muscle (F_{(3, 78)} = 7.13, P < 0.001, η2p = 0.21), exercise × velocity (F_{(1, 26)} = 12.06, P = 0.002, η2p = 0.31), contraction type × velocity (F_{(1, 26)} = 148.29, P < 0.001, η2p = 0.85), and exercise × contraction type × velocity (F_{(1, 26)} = 20.14, P < 0.001, η2p = 0.43).

Figure 1.

Comparison of the muscle activation during the negative phase for each muscle (%MVC) under the conditions performed at both velocities for men and women (*difference between velocities; P < 0.05). GMED, gluteus medialis; MVC, maximum voluntary contraction; RF, rectus femoris; VL, vastus lateralis; VMO, vastus medialis oblique.

Figure 2.

Comparison of the muscle activation during the positive phase for each muscle (%MVC) under the conditions performed at both velocities for men and women (*difference between velocities; P < 0.05). GMED, gluteus medialis; MVC, maximum voluntary contraction; RF, rectus femoris; VL, vastus lateralis; VMO, vastus medialis oblique.

Muscle activation (%MVC) under each condition was similar between men and women for each muscle; significant differences were only found in 3 cases (P < 0.05): the 0° 100% and 45° 100% negative phase of the maximum velocity sets for the GMED, and the 45° 100% positive phase of the maximum velocity set for the RF (Figures 1 and 2). Muscle activation was greater under the maximum intended velocity conditions than under the steady-paced conditions in almost all cases and for both contraction types. Furthermore, in all cases, muscle activation (%MVC) was significantly greater (P < 0.05) in the positive phase than in the negative phase.

When comparing the muscle activation in the positive phase between muscles (%MVC) in men and women under the 3 conditions performed at steady-paced velocity, only the VL presented greater muscle activation (P < 0.05) in men than in women under the 0° 150% condition. In contrast, muscle activation in the negative phase showed no significant differences (P > 0.05) between the 3 steady-paced conditions.

Figures 3 and 4 show a comparison of positive phase muscle activation between muscles (%MVC) under each steady-paced condition for men and women. The ANOVA (gender × exercise × muscle) results showed a significant main effect/interaction for muscle (F_{(3, 78)} = 62.00, P < 0.001, η2p = 0.70), gender × muscle (F_{(3, 78)} = 4.69, P = 0.005, η2p = 0.15), exercise (F_{(2, 52)} = 4.86, P = 0.012, η2p = 0.15), and exercise × muscle (F_{(6, 156)} = 3.78, P = 0.002, η2p = 0.12).

Figure 3.

Comparison of the muscle activation during the positive phase between muscles (%MVC) for each condition performed at a steady-paced velocity for the men (adifference from VMO, bdifference from VL, cdifference from RF; P < 0.05). GMED, gluteus medialis; MVC, maximum voluntary contraction; RF, rectus femoris; VL, vastus lateralis; VMO, vastus medialis oblique.

Figure 4.

Comparison of muscle activation during the positive phase between muscles (%MVC) for each condition performed at a steady-paced velocity for the women (adifference from VMO, bdifference from VL, cdifference from RF; P < 0.05). GMED, gluteus medialis; MVC, maximum voluntary contraction; RF, rectus femoris; VL, vastus lateralis; VMO, vastus medialis oblique.

The muscle activation pattern was similar under all 3 steady-paced conditions (0° 100%, 45° 100%, and 0° 150%) for the positive phase in each gender group, whereas each muscle presented no significant differences (P > 0.05) between the 3 conditions in either men or women. Negative phase muscle activation likewise presented no significant differences (P > 0.05) between the conditions for any muscle. Therefore, variations in stance width and/or feet rotation did not affect the muscle activation elicited. However, slight differences were found for the muscle activation pattern between men and women. While in men, VMO showed the greatest muscle activation followed by VL, RF, and GMED, in women, the greatest muscle activation was presented by VMO, followed by RF, VL, and GMED.

Kinematic Parameters

Table 2 shows a comparison of MPV and V_max between the conditions executed at maximum intended velocity. The paired sample t test results showed significantly greater MPV under the 0° 100% maximum intended velocity condition compared with the 45° 100% maximum intended velocity condition in men and women. Moreover, V_max was significantly greater under the 0° 100% maximum intended velocity condition in women. Both the MPV and V_max variables were significantly greater for men than for women in all cases (P < 0.05).

Table 2.

Comparison of MPV and V_max under the conditions executed at maximum intended velocity (mean ± SD)a

		Maximum Intended Velocity 0° 100%	Maximum Intended Velocity 45° 100%	P	Effect Size (d)
Male	MPV (m/s)	0.43 ± 0.06	0.39 ± 0.06	0.002	0.66
	Vmax (m/s)	0.85 ± 0.12	0.82 ± 0.12	0.05	0.25
Female	MPV (m/s)	0.37 ± 0.05	0.33 ± 0.05	<0.001	0.80
	Vmax (m/s)	0.76 ± 0.08	0.72 ± 0.09	<0.001	0.46

MPV, mean propulsive velocity; Vmax, maximum velocity.

^aBoth variables presented statistically significant differences between the genders (P < 0.05).

Table 3 shows a comparison of P_max under the conditions executed at steady-paced velocity. The ANOVA (gender × exercise × velocity) results showed a significant main effect for gender (F_{(1, 26)} = 32.38, P < 0.001, η2p = 0.55) and for exercise (F_{(2, 52)} = 5.47, P = 0.007, η2p = 0.17). Significant differences (P < 0.05) were found under the 0° 100% and 45° 100% steady-paced conditions for men, while P_max was greater under the 45° 100% condition. Otherwise, men elicited significantly greater P_max under all the conditions than the women (P < 0.05).

Table 3.

Comparison of P_max under the conditions executed at a steady-paced velocity (mean ± SD)^a

		0° 100%	45° 100%	0° 150%
Pmax (W)	Male	488.9 ± 132.6 b	560.8 ± 169.6 b , c	512.3 ± 123.2
	Female	288.4 ± 44.7	323.8 ± 79.3	294.6 ± 59.3

P_max, maximum power.

^aBoth variables presented statistically significant differences between the genders (P < 0.05).

^bIndicates significant differences with regard to 0° 150% (P < 0.05).

^cIndicates significant differences with respect to 0° 100% (P < 0.05).

Table 4 shows a comparison of P_max between the conditions executed at both maximum intended velocity and steady-paced velocity. The ANOVA (gender × exercise × velocity) results showed a main effect/interaction on P_max for gender (F_{(1, 26)} = 37.37, P < 0.001, η2p = 0.59), velocity (F_{(1, 26)} = 559.68, P < 0.001, η2p = 0.95), and gender × velocity (F_{(1, 26)} = 23.02, P < 0.001, η2p = 0.47). No differences (P > 0.05) were found under the conditions performed at maximum intended velocity for P_max in either men or women. However, men presented significantly greater P_max values than women in all cases (Table 4).

Table 4.

Comparison of P_max under the conditions executed at both maximum intended velocity and steady-paced velocity (mean ± SD)^a

			0° 100%	45° 100%	P	Effect Size (d)
Male	Pmax (W)	Maximum intended velocity	1556.8 ± 295.8	1665.9 ± 412.9	0.13	0.30
		Steady-paced velocity	488.9 ± 132.6	560.8 ± 169.6	0.02	0.47
Female	Pmax (W)	Maximum intended velocity	1056.7 ± 189.1	995.8 ± 195.8	0.43	0.31
		Steady-paced velocity	288.4 ± 44.7	323.8 ± 79.2	0.18	0.55

P_max, maximum power.

^aAll variables presented statistically significant differences between velocities and genders (P < 0.001).

Figure 5 shows the data for footplate displacement and time kinematics under all the conditions during both the negative and the positive phases. The ANOVA (gender × exercise × contraction type) results showed a main effect/interaction on displacement for exercise (F_{(4, 104)} = 31.69, P < 0.001, η2p = 0.54), contraction type (F_{(1, 26)} = 112.94, P < 0.001, η2p = 0.81), gender × contraction type (F_{(1, 26)} = 17.39, P < 0.001, η2p = 0.40), and exercise × contraction type (F_{(4, 104)} = 28.57, P < 0.001, η2p = 0.52). Men presented higher footplate displacement in the positive phases than women under all the conditions (P < 0.05), whereas footplate displacement in the negative phase presented no significant differences between genders (P > 0.05). Furthermore, the maximum intended velocity conditions presented significantly greater footplate displacement than the steady-paced conditions in both men and women (P < 0.05).

Figure 5.

Displacement and time kinematic data for all conditions during both the negative and positive phases.

The ANOVA (gender × exercise × contraction type) results showed a main effect on time for exercise (F_{(4, 104)} = 97.33, P < 0.001, η2p = 0.78), and contraction type (F(_{1, 26}) = 91.66, P < 0.001, η2p = 0.77). No significant differences for time were found between genders in any movement phase (P > 0.05), whereas the positive phases presented shorter times under all conditions (P < 0.05). In addition, the positive phases were performed faster under the maximum intended velocity conditions than under the steady-paced conditions in both genders (P < 0.05).

Discussion

Despite the belief that variations in feet stance might affect muscle activation during the leg press exercise, our results suggested that such modifications might be meaningless if our training aim is to elicit preferential activation of 1 particular muscle over the rest. Our results agree with those reported by Escamilla et al, ¹³ who found no changes in muscle activation based on the feet abduction position. ²⁸ If the aim is to focus on a specific muscle, one might, for instance, modify or limit the range of motion in the leg press exercise, as it has been widely reported that the vastus medialis, VL, and RF elicit their greatest muscle activation during the first part of the extension phase.^17,18,28,52

The fact that there is greater muscle activation in the positive phases of the movement is broadly supported in the literature; this is partly explained by the major recruitment of muscle fibers that this phase requires.^{2,17,23,26,29,37} On the other hand, the greater muscle activation elicited under maximal intended conditions is in accordance with the results reported by Walker et al, ⁵² who found greater muscle activation under explosive contractions. Nonetheless, this issue has hardly been assessed. ¹⁹

Several studies have raised concerns regarding gender differences on lower body biomechanics, ⁵¹ neuromuscular function and muscle activation imbalances, ³⁶ or decreased relative quadriceps muscle activation in men rather than women. ³⁵ Even though overall muscle activation was greater for men in absolute terms (raw µV), when normalized to %MVC, the muscle activation pattern was very similar between genders. Therefore, we might conclude that the muscle activation pattern differs only slightly between men and women when performing the inclined leg press exercise. For both gender groups, VMO presented the greatest muscle activation while GMED presented the lowest. Regarding differences in the VL, in the male group, greater muscle activation was presented, followed by RF; in the female group, the opposite was true. This information may guide coaches and practitioners when selecting the specific exercise and range of motion. Nonetheless, we confirmed that the inclined leg press is an optimal exercise for targeting muscle activation in the entire quadriceps muscle complex.^{11,13,16,26,50,52}

In terms of the kinematic parameters, we reported greater MPV, V_max, and P_max values for men than for women under all the conditions. In addition, MPV and V_max were greater under the 0° 100% maximum intended velocity condition than under the 45° 100% maximum intended velocity condition for both gender groups. Gender differences in MPV, V_max, and P_max are not surprising since the anthropometric measures and basal neuromuscular capabilities for exerting force are greater in men than in women.^19,36 However, it is worth noting that the 0° 100% feet stance was reported by all participants as being the most comfortable, which might lead one to conclude that the preferred feet stance should be encouraged to enhance performance. Women were more affected by variations in feet stance; for instance, they reported greater discomfort under the 45° external rotation condition.

Footplate displacement was greater in the positive phases for men under all conditions, whereas, in the negative phase, there was no difference between men and women. Furthermore, greater footplate displacements were reported under maximum intended velocity conditions than under steady-paced conditions for all participants. Finally, no significant differences in movement times were reported between men and women, while the positive phases were faster under all conditions and in both gender groups. The greater displacement in the positive phases under the maximum intended velocity conditions is explained by the inertia elicited on the explosive contractions, which even produced noncontact time between the feet and the footplate. This is to some extent related to the flight time during a jumping or landing task.^1,9,27,30

Leg press has been defined as a safe ballistic movement, which stimulates jump biomechanics.^30,47 The ability to exert the maximum power during a dynamic multijoint movement would depend on the nature of the movement per se. ¹⁰ Thus, the exercises selected for a training program would modulate adaptations and improvements in sports performance.^10,30,47

Maximal power during a movement might be enhanced by increasing the ability to exert greater levels of force at a given velocity.^10,30 Since sports-related movements usually demand greater power requirements, it might be more beneficial to include explosive movements in the training program to maximize sports-related skills transference and enhance performance.^15,22,42

Limitations

Some of limitations encountered during the measurements were related to the performance of the steady-paced condition rhythm. Most people were not used to carefully controlling their MV, so extra time was needed with each participant during the prior familiarization session to ensure they had mastered the proper technique and pace. Another issue arose during the pilot study, which included the 45° 150% maximum velocity condition and the 0° 150% maximum intended condition. Unfortunately, the footplate size did not allow us to perform these conditions because, in most cases, the subjects’ feet did not fit into the footplate; as a result, we decided to eliminate this condition. Furthermore, a sample of trained young college students was tested, so our results should be interpreted with caution, being only extrapolated to a population with similar characteristics.

Conclusion

Overall, the muscle activation pattern presented no significant differences between conditions regarding feet width stance and feet external rotation for 0° 100% and 45° 100% performed at both velocities within each gender group. The positive phase presented greater muscle activation and faster under all conditions in both gender groups than the negative phase for the different conditions, whereas muscle activation for the maximum intended velocity sets was greater than those elicited during steady-paced contractions.

Regarding the kinematic parameters, MPV, V_max, and P_max presented significantly greater values in the male population under all conditions. Furthermore, MPV and V_max were greater under the 0° 100% maximum intended velocity condition than under the 45° 100% maximum intended velocity condition in both men and women.