Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position

Acute muscle excitation response across various bench press ranges of motion

This study examined muscle excitation using surface electromyography (sEMG) during different ranges of motion (ROM) in the bench press. Given the limited research on upper-body muscle excitation across ROMs, this study aimed to establish reference values for muscle excitation in distinct bench press ROMs. Nineteen male participants performed a 10-repetition maximum (10RM) bench press across three ROMs: full ROM, upper-half ROM, and lower-half ROM. sEMG measurements were taken on the pectoralis major (PM), triceps brachii (TB), and anterior deltoid (AD). Mean and peak EMG amplitudes were analyzed. Significant differences in mean muscle excitation were observed across all muscles (p < 0.001-0.002). The upper-half ROM elicited the highest mean excitation for the TB, while both partial ROMs resulted in greater excitation for the PM and AD compared to the full ROM. Peak muscle excitation was significantly greater in the PM sternocostal 15% region during the upper-half ROM. Additionally, the TB long and lateral heads showed significantly higher peak EMG values in the upper-half ROM than in the other conditions. These results suggest that ROM variations in the bench press lead to distinct muscle excitation patterns. This insight may inform future research on ROM's effects on muscle hypertrophy and strength development.

Comparison Between Shoulder Flexed and Extended Positions in Elbow Flexion Resistance Training on Regional Hypertrophy and Maximum Strength: Preacher versus Bayesian Cable Curls

In the present study, the effects of resistance training on regional hypertrophy and maximum strength of the elbow flexor muscles were compared between elbow flexion exercises performed with different shoulder joint angles (∼50° of flexion vs. extension) while matched for resistance profiles. In a within-subject design, 15 young men (25.6 ± 2.1 y; 77.3 ± 6.8 kg; 175.1 ± 5.7 cm) underwent a resistance training program twice a week for 10 weeks (3-5 sets, 8-12RM), and their arms were dominant-side balanced, randomly assigned to one of the two conditions according to elbow flexion exercises: unilateral cable curl with shoulder flexed (Preacher curl; PREA) or unilateral cable curl with shoulder extended (Bayesian curl; BAYE). B-mode ultrasound imaging was used to measure changes in muscle thickness of the biceps brachii and brachialis at proximal, mid, and distal arm regions, and one-repetition maximum tests were completed in each respective trained exercise before and after training. Both conditions showed significant increases in muscle thickness (p < 0.05) with no significant differences between them (p > 0.05) across the biceps brachii proximal, mid, and distal regions (relative change [Hedges' g effect size]; PREA: 6%[0.51], 7%[0.49], 7%[0.53]; BAYE: 9%[0.73], 9%[0.62], 9%[0.62]) and brachialis (PREA: 10%[0.72]; BAYE: 8%[0.65]). Similarly, significant improvements in maximum strength were observed (p < 0.05), with equivalent results between conditions (PREA: 28%[0.85], BAYE: 37%[1.22]; equivalence testing, p-values = 0.061, 0.637). In conclusion, the shoulder joint angle does not seem to affect muscle hypertrophy and maximum strength gains after different elbow flexion exercises matched for resistance profiles.

Distinct muscle growth and strength adaptations after preacher and incline biceps curls

We compared performing preacher and incline biceps curls on changes in elbow flexor muscle size and strength. This was a between-group repeated measure randomized trial. Sixty-three young women performed the preacher biceps curl (n=30) or the incline biceps curl (n=33) for 8 weeks, twice a week. We measured the muscle thickness of elbow flexors at the proximal, middle, and distal sites. We assessed the muscle strength using three repetition maximum tests in the preacher curl and the incline curl. We observed a greater increase in the proximal elbow flexor thickness in the incline biceps curl compared to the preacher biceps curl (mean difference=0.08 cm [95% confidence interval: 0.02, 0.13 cm]). We observed a greater increase in the distal elbow flexor thickness in the preacher biceps curl compared to the incline biceps curl (mean difference=0.10 cm [95%CI: 0.04, 0.15 cm]). The preacher biceps curl showed a greater increase in three repetition maximum tests in the preacher curl (mean difference=1.88 kg [95%CI: 1.14, 2.62 kg]). The incline biceps curl showed a greater increase in three repetition maximum tests in the incline biceps curl (mean difference=0.86 kg [95%CI: 0.10, 1.62 kg]). Our findings suggest regional differences in muscle growth induced by the preacher and incline biceps curls. Strength gains appear to follow the principle of specificity.

Lengthened partial repetitions elicit similar muscular adaptations as full range of motion repetitions during resistance training in trained individuals

Purpose

Resistance training using different ranges of motion may produce varying effects on musclular adaptations. The purpose of this study was to compare the effects of lengthened partial repetitions (LPs) vs. full range of motion (ROM) resistance training (RT) on muscular adaptations.

Methods

In this within-participant study, thirty healthy, resistance-trained participants had their upper extremities randomly assigned to either a lengthened partial or full ROM condition; all other training variables were equivalent between limbs. The RT intervention was an 8-week program targeting upper-body musculature. Training consisted of two training sessions per week, with four exercises per session and four sets per exercise. Muscle hypertrophy of the elbow flexors and elbow extensors was evaluated using B-mode ultrasonography at 45% and 55% of humeral length. Muscle strength-endurance was assessed using a 10-repetition-maximum test on the lat pulldown exercise, both with a partial and full ROM. Data analysis employed a Bayesian framework with inferences made from posterior distributions and the strength of evidence for the existence of a difference through Bayes factors.

Results

Both muscle thickness and unilateral lat pulldown 10-repetition-maximum improvements were similar between the two conditions. Results were consistent across outcomes with point estimates close to zero, and Bayes factors (0.16 to 0.3) generally providing "moderate" support for the null hypothesis of equal improvement across interventions.

Conclusions

Trainees seeking to maximize muscle size should likely emphasize the stretched position, either by using a full ROM or LPs during upper-body resistance training. For muscle strength-endurance, our findings suggest that LPs and full ROM elicit similar adaptations.

The effects of hip flexion angle on quadriceps femoris muscle hypertrophy in the leg extension exercise

This study compared the effects of 90° versus 40° hip flexion in the leg extension exercise on quadriceps femoris muscle hypertrophy. Twenty-two untrained men completed a ten-week intervention comprising two resistance training sessions per week. A within-participant design was used, with the lower limb side randomly allocated to the 40 or 90° condition. Muscle thickness of distal and proximal rectus femoris and vastus lateralis was quantified via ultrasound. Data were analysed within a Bayesian framework including univariate and multivariate mixed effect models with random effects to account for the within participant design. Differences between conditions were estimated as average treatment effects (ATE) and inferences were made based on posterior distributions and Bayes Factors (BF). Results indicated a greater hypertrophic response in the rectus femoris for the 40° condition, with "extreme" evidence supporting a hypertrophic response favouring the 40° hip angle for the rectus femoris (BF > 100; p(Distal/ATE & Proximal/ATE >0) > 0.999), and "strong" evidence supporting no difference in hypertrophic response for the vastus lateralis (BF = 0.07). Therefore, both conditions could be viable options for increasing quadriceps femoris hypertrophy. However, when training for maximizing rectus femoris hypertrophy among untrained men, we suggest training with a reduced hip flexion in the leg extension exercise.

Similar Regional Hypertrophy of the Elbow Flexor Muscles in Response to Low-Load Training With Vascular Occlusion at Short Versus Long Muscle Lengths

BACKGROUND

The regional hypertrophy response of elbow flexor muscles was compared after unilateral elbow flexion training in extended versus flexed shoulder position under vascular occlusion, which can induce muscle hypertrophy in the absence of muscle damage-induced edema/swelling.

HYPOTHESIS

Hypertrophy of elbow flexor muscles would be greater in extended compared with flexed shoulder position.

STUDY DESIGN

Randomized within-subject trial.

LEVEL OF EVIDENCE

Level 2.

METHODS

A total of 21 resistance-trained men (age, 25 ± 5 years; height, 1.78 ± 0.07 m; weight, 79.3 ± 13.1 kg) performed unilateral elbow flexions with one shoulder extended/elbow flexor muscles lengthened/long muscle length (LONG) and the other flexed/elbow flexor muscles shortened/short muscle length (SHORT) under a low-load (30% 1-repetition maximum) vascular occlusion training regimen (15 repetitions per set, 4 sets per session, 4 sessions per week for 3 weeks, using 80% of vascular occlusion pressure). Magnetic resonance imaging measured elbow flexor muscles cross-sectional area (EFCSA) pre- and post-training at 45%, 65%, and 85% of humerus length.

RESULTS

EFCSA significantly increased in both SHORT (P = 0.04) and LONG (P = 0.05) at 45% and 85% lengths (P < 0.01 for both). Changes in EFCSA between SHORT and LONG were statistically similar at the 45% (+6.20% vs +5.08%; Cohen d = 0.006; P = 0.98), 65% (+5.91% vs +3.83%, Cohen d = 0.28, P = 0.30), and 85% lengths (+8.51% vs +7.38%, Cohen d = 0.18,P = 0.56).

CONCLUSION

Muscle hypertrophy of the elbow flexor muscles displayed a similar behavior after low-load elbow flexion training with vascular occlusion performed in the extended versus flexed shoulder position.

CLINICAL RELEVANCE

Therapists, clinicians, and coaches may choose elbow flexion exercises expecting to achieve similar results for hypertrophy in this muscle group, such that exercise selection may rely on availability of equipment in the training room or personal preference.

Muscle Hypertrophy and Strength Adaptations to Systematically Varying Resistance Exercises

We compared the effects of varied and constant resistance exercises on muscular adaptations in young women. Seventy young women (21.8 ± 3.4 yrs, 62.0 ± 12.3 kg, 162.3 ± 5.7 cm) were randomly divided into two groups: constant resistance exercises (CON-RE, n = 38) or varied resistance exercises (VAR-RE, n = 32). The resistance training (RT) was performed thrice a week over 10 weeks. CON-RE performed a 45º leg press and stiff-leg deadlift in every training session, while VAR-RE performed 45º leg press and stiff-leg deadlift in the first training session of the week, hack squat and prone leg curl in the second, and Smith machine squat and seated-leg curl in the third. Both groups performed two sets of 10-15 repetitions maximum per resistance exercise. We measured the muscle thickness of the thigh's anterior, lateral, and posterior aspects by ultrasonography at different muscle sites (proximo-distal). Muscular strength was analyzed from the one-repetition maximum (1RM) tests in the 45° leg press and leg extension (non-trained exercise). The muscle thickness increased similarly in both groups for all muscles and sites (CON-RE: +7.8-17.7% vs. VAR-RE: +7.5-19.3%, p > .05). The 1RM increased similarly in both groups (CON-RE: +24.4-32.1% vs. VAR-RE: +29.0-30.1%, p > .05). Both RT routines resulted in virtually similar muscular strength gains and hypertrophy. Therefore, both strategies should be considered for the improvement of strength and muscle growth.

Hamstrings Hypertrophy Is Specific to the Training Exercise: Nordic Hamstring versus Lengthened State Eccentric Training

INTRODUCTION

The hamstring muscles play a crucial role in sprint running but are also highly susceptible to strain injuries, particularly within the biceps femoris long head (BFlh). This study compared the adaptations in muscle size and strength of the knee flexors, as well as BFlh muscle and aponeurosis size, after two eccentrically focused knee flexion training regimes: Nordic hamstring training (NHT) vs lengthened state eccentric training (LSET, isoinertial weight stack resistance in an accentuated hip-flexed position) vs habitual activity (no training controls: CON).

METHODS

Forty-two healthy young males completed 34 sessions of NHT or LSET over 12 wk or served as CON ( n = 14/group). Magnetic resonance imaging-measured muscle volume of seven individual knee flexors and BFlh aponeurosis area, and maximum knee flexion torque during eccentric, concentric, and isometric contractions were assessed pre- and post-training.

RESULTS

LSET induced greater increases in hamstrings (+18% vs +11%) and BFlh (+19% vs +5%) muscle volumes and BFlh aponeurosis area (+9% vs +3%) than NHT (all P ≤ 0.001), with no changes after CON. There were distinctly different patterns of hypertrophy between the two training regimes, largely due to the functional role of the muscles; LSET was more effective for increasing the size of knee flexors that also extend the hip (2.2-fold vs NHT), whereas NHT increased the size of knee flexors that do not extend the hip (1.9-fold vs LSET; both P ≤ 0.001). Changes in maximum eccentric torque differed only between LSET and CON (+17% vs +4%; P = 0.009), with NHT (+11%) inbetween.

CONCLUSIONS

These results suggest that LSET is superior to NHT in inducing overall hamstrings and BFlh hypertrophy, potentially contributing to better sprint performance improvements and protection against hamstring strain injuries than NHT.

Progression of total training volume in resistance training studies and its application to skeletal muscle growth

Progressive overload describes the gradual increase of stress placed on the body during exercise training, and is often quantified (i.e. in resistance training studies) through increases in total training volume (i.e. sets × repetitions × load) from the first to final week of the exercise training intervention. Within the literature, it has become increasingly common for authors to discuss skeletal muscle growth adaptations in the context of increases in total training volume (i.e. the magnitude progression in total training volume). The present manuscript discusses a physiological rationale for progressive overload and then explains why, in our opinion, quantifying the progression of total training volume within research investigations tells very little about muscle growth adaptations to resistance training. Our opinion is based on the following research findings: (1) a noncausal connection between increases in total training volume (i.e. progressively overloading the resistance exercise stimulus) and increases in skeletal muscle size; (2) similar changes in total training volume may not always produce similar increases in muscle size; and (3) the ability to exercise more and consequently amass larger increases in total training volume may not inherently produce more skeletal muscle growth. The methodology of quantifying changes in total training volume may therefore provide a means through which researchers can mathematically determine the total amount of external 'work' performed within a resistance training study. It may not, however, always explain muscle growth adaptations.

Determining Changes in Muscle Size and Architecture After Exercise Training: One Site Does Not Fit all

ABSTRACT

Nunes, JP, Blazevich, AJ, Schoenfeld, BJ, Kassiano, W, Costa, BDV, Ribeiro, AS, Nakamura, M, Nosaka, K, and Cyrino, ES. Determining changes in muscle size and architecture after exercise training: One site does not fit all. J Strength Cond Res 38(4): 787-790, 2024-Different methods can be used to assess muscle hypertrophy, but the effects of training on regional changes in muscle size can be detected only using direct muscle measurements such as muscle thickness, cross-sectional area, or volume. Importantly, muscle size increases vary across regions within and between muscles after resistance training programs (i.e., heterogeneous, or nonuniform, muscle hypertrophy). Muscle architectural changes, including fascicle length and pennation angle, after resistance and stretch training programs are also region-specific. In this paper, we show that the literature indicates that a single-site measure of muscle shape does not properly capture the effects achieved after exercise training interventions and that conclusions concerning the magnitude of muscle adaptations can vary substantially depending on the muscle site to be examined. Thus, we propose that measurements of muscle size and architecture should be completed at multiple sites across regions between the agonist muscles within a muscle group and along the length of the muscles to provide an adequate picture of training effects.

Triceps surae muscle hypertrophy is greater after standing versus seated calf-raise training

Background: The triceps surae muscle plays important roles in fundamental human movements. However, this muscle is relatively unresponsive to resistance training (difficult to hypertrophy) but prone to atrophy with inactivity compared with other muscles. Thus, identifying an effective training modality for the triceps surae is warranted. This study compared triceps surae muscle hypertrophy after standing/knee-extended versus seated/knee-flexed plantarflexion (calf-raise) training, where the gastrocnemius is lengthened and shortened, respectively. Methods: Fourteen untrained adults conducted calf-raise training with one leg in a standing/knee-extended position and the other leg in a seated/knee 90°-flexed position at 70% of one-repetition maximum. Each leg performed 10 repetitions/set, 5 sets/session, 2 sessions/week for 12 weeks. Before and after the intervention, magnetic resonance imaging scans were obtained to assess muscle volume of each and the whole triceps surae. Results: Muscle volume significantly increased in all three muscles and the whole triceps surae for both legs (p ≤ 0.031), except for the gastrocnemius muscles of the seated condition leg (p = 0.147-0.508). The changes in muscle volume were significantly greater for the standing than seated condition leg in the lateral gastrocnemius (12.4% vs. 1.7%), medial gastrocnemius (9.2% vs. 0.6%), and whole triceps surae (5.6% vs. 2.1%) (p ≤ 0.011), but similar between legs in the soleus (2.1% vs. 2.9%, p = 0.410). Conclusion: Standing calf-raise was by far more effective, therefore recommended, than seated calf-raise for inducing muscle hypertrophy of the gastrocnemius and consequently the whole triceps surae. This result and similar between-condition hypertrophy in the soleus collectively suggest that training at long muscle lengths promotes muscle hypertrophy.

Pectoralis major and triceps brachii cross-sectional area measured on different planes: the effect on the muscle size-strength relationship

BACKGROUND

Magnetic resonance imaging (MRI) is a well-used technique to assess muscle size and can be acquired on different planes. Pectoralis major (PM) and triceps brachii (TB) muscles are often acquired and analyzed on the axial plane, however it is unknown if anatomical cross-sectional area (CSA) calculated from different planes will affect the muscle size-strength relationship. Thus, the first aim of the present study was to identify if the CSA of the PM and TB measured on different planes presents a similar muscle size-strength relationship. A secondary aim was to investigate if the quantification of CSA of the PM and TB muscles are similar between sagittal and axial plane.

METHODS

Fifteen males underwent an MRI examination, and after that, one-repetition maximum (1RM) test was performed.

RESULTS

There was a significant relationship between 1RM and PM CSA measured on the axial and sagittal plane (r≤0.81), while the relationship with TB CSA was only good on the axial plane (r=0.65) and not significant on the sagittal plane (r=0.27). ICC between planes was excellent for PM CSA (0.96) with Bland-Altman procedure showing agreement between planes (d=0.376; P=0.612). Contrarily, TB CSA ICC was week (0.07), with Bland-Altman procedure showing no agreement between planes (d=-24.49; P=0.022).

CONCLUSIONS

CSA measured at axial plane from PM and TB muscles showed a significant relationship with 1RM, while only PM CSA on the sagittal plane showed a significant relationship with 1RM. Finally, it was demonstrated that PM images showed a great reliability between planes, which was not true for TB muscle.

Hip thrust and back squat training elicit similar gluteus muscle hypertrophy and transfer similarly to the deadlift

We examined how set-volume equated resistance training using either the back squat (SQ) or hip thrust (HT) affected hypertrophy and various strength outcomes. Untrained college-aged participants were randomized into HT (n = 18) or SQ (n = 16) groups. Surface electromyograms (sEMG) from the right gluteus maximus and medius muscles were obtained during the first training session. Participants completed 9 weeks of supervised training (15-17 sessions), before and after which gluteus and leg muscle cross-sectional area (mCSA) was assessed via magnetic resonance imaging. Strength was also assessed prior to and after the training intervention via three-repetition maximum (3RM) testing and an isometric wall push test. Gluteus mCSA increases were similar across both groups. Specifically, estimates [(-) favors HT (+) favors SQ] modestly favored the HT versus SQ for lower [effect ±SE, -1.6 ± 2.1 cm2; CI95% (-6.1, 2.0)], mid [-0.5 ± 1.7 cm2; CI95% (-4.0, 2.6)], and upper [-0.5 ± 2.6 cm2; CI95% (-5.8, 4.1)] gluteal mCSAs but with appreciable variance. Gluteus medius + minimus [-1.8 ± 1.5 cm2; CI95% (-4.6, 1.4)] and hamstrings [0.1 ± 0.6 cm2; CI95% (-0.9, 1.4)] mCSA demonstrated little to no growth with small differences between groups. mCSA changes were greater in SQ for the quadriceps [3.6 ± 1.5 cm2; CI95% (0.7, 6.4)] and adductors [2.5 ± 0.7 cm2; CI95% (1.2, 3.9)]. Squat 3RM increases favored SQ [14 ± 2 kg; CI95% (9, 18),] and hip thrust 3RM favored HT [-26 ± 5 kg; CI95% (-34, -16)]. 3RM deadlift [0 ± 2 kg; CI95% (-4, 3)] and wall push strength [-7 ± 12N; CI95% (-32, 17)] similarly improved. All measured gluteal sites showed greater mean sEMG amplitudes during the first bout hip thrust versus squat set, but this did not consistently predict gluteal hypertrophy outcomes. Squat and hip thrust training elicited similar gluteal hypertrophy, greater thigh hypertrophy in SQ, strength increases that favored exercise allocation, and similar deadlift and wall push strength increases.

Greater Gastrocnemius Muscle Hypertrophy After Partial Range of Motion Training Performed at Long Muscle Lengths

ABSTRACT

Kassiano, W, Costa, B, Kunevaliki, G, Soares, D, Zacarias, G, Manske, I, Takaki, Y, Ruggiero, MF, Stavinski, N, Francsuel, J, Tricoli, I, Carneiro, MAS, and Cyrino, ES. Greater gastrocnemius muscle hypertrophy after partial range of motion training performed at long muscle lengths. J Strength Cond Res 37(9): 1746-1753, 2023-Whether there is an optimal range of motion (ROM) to induce muscle hypertrophy remains elusive, especially for gastrocnemius. This study aimed to compare the changes in gastrocnemius muscle thickness between calf raise exercise performed with full ROM (FULL ROM ), partial ROM performed in the initial (INITIAL ROM ), and final (FINAL ROM ) portions of the ROM. Forty-two young women performed a calf training program for 8 weeks, 3 days·week -1 , with differences in the calf raise ROM configuration. The calf raise exercise was performed in a pin-loaded, horizontal, leg-press machine, in 3 sets of 15-20 repetition maximum. The subjects were randomly assigned to 1 of the 3 groups: FULL ROM (ankle: -25° to +25°), INITIAL ROM (ankle: -25° to 0°), and FINAL ROM (ankle: 0° to +25°), where 0° was defined as an angle of 90° of the foot with the tibia. The muscle thickness measurements of medial and lateral gastrocnemius were taken by means of B-mode ultrasound. INITIAL ROM elicited greater medial gastrocnemius increases than FULL ROM and FINAL ROM (INITIAL ROM = +15.2% vs. FULL ROM = +6.7% and FINAL ROM = +3.4%; p ≤ 0.009). Furthermore, INITIAL ROM elicited greater lateral gastrocnemius increases than FINAL ROM (INITIAL ROM = +14.9% vs. FINAL ROM = +6.2%; p < 0.024) but did not significantly differ from FULL ROM (FULL ROM = +7.3%; p = 0.060). The current results suggest that calf training performed at longer muscle lengths may optimize gastrocnemius muscle hypertrophy in young women. Therefore, when prescribing hypertrophy-oriented training, the inclusion of the calf raise exercise performed with partial ROM in the initial portion of the excursion should be considered.

Hip thrust and back squat training elicit similar gluteus muscle hypertrophy and transfer similarly to the deadlift

Purpose

We examined how set-volume equated resistance training using either the back squat (SQ) or hip thrust (HT) affected hypertrophy and various strength outcomes.

Methods

Untrained college-aged participants were randomized into HT or SQ groups. Surface electromyograms (sEMG) from the right gluteus maximus and medius muscles were obtained during the first training session. Participants completed nine weeks of supervised training (15-17 sessions), before and after which we assessed muscle cross-sectional area (mCSA) via magnetic resonance imaging and strength via three-repetition maximum (3RM) testing and an isometric wall push test.

Results

Glutei mCSA growth was similar across both groups. Estimates [(-) favors HT; (+) favors SQ] modestly favored the HT compared to SQ for lower [effect ± SE, -1.6 ± 2.1 cm2], mid [-0.5± 1.7 cm2], and upper [-0.5 ± 2.6 cm2], but with appreciable variance. Gluteus medius+minimus [-1.8 ± 1.5 cm2] and hamstrings [0.1 ± 0.6 cm2] mCSA demonstrated little to no growth with small differences between groups. Thigh mCSA changes were greater in SQ for the quadriceps [3.6 ± 1.5 cm2] and adductors [2.5 ± 0.7 cm2]. Squat 3RM increases favored SQ [14 ± 2.5 kg] and hip thrust 3RM favored HT [-26 ± 5 kg]. 3RM deadlift [0 ± 2 kg] and wall push strength [-7 ± 13 N] similarly improved. All measured gluteal sites showed greater mean sEMG amplitudes during the first bout hip thrust versus squat set, but this did not consistently predict gluteal hypertrophy outcomes.

Conclusion

Nine weeks of squat versus hip thrust training elicited similar gluteal hypertrophy, greater thigh hypertrophy in SQ, strength increases that favored exercise allocation, and similar strength transfers to the deadlift and wall push.

Hip flexion angle affects longitudinal muscle activity of the rectus femoris in leg extension exercise

PURPOSE

We investigated the effect of the hip flexion angle (HFA) on the longitudinal muscle activity of the rectus femoris (RF) during leg extension exercise (LEE).

METHODS

We conducted an acute study in a specific population. Nine male bodybuilders performed isotonic LEE using a leg extension machine at three different HFAs: 0°, 40°, and 80°. Participants extended their knees from 90° to 0° at each HFA setting for four sets of ten repetitions at 70% of the one-repetition maximum. The transverse relaxation time (T2) of the RF was measured before and after LEE using magnetic resonance imaging. We analyzed the rate of change in the T2 value in the proximal, middle, and distal regions of the RF. The subjective sensation of muscle contraction of the quadriceps was measured using a numerical rating scale (NRS) and compared with the T2 value which was the objective index.

RESULTS

At 80°, the T2 value in the middle RF was lower than that in the distal RF (p < 0.05). The T2 values at 0° and 40° HFA were higher than those at 80° HFA in the proximal (p < 0.05, p < 0.01) and middle RF (p < 0.01, p < 0.01). The NRS scores were inconsistent with the objective index.

CONCLUSION

These results suggest that the 40° HFA is practical for region-specific strengthening of the proximal RF, and subjective sensation alone as an indication of training may not activate the proximal RF. We conclude that activation of each longitudinal section of the RF is possible depending on the hip joint angle.