Do exercise-induced increases in muscle size contribute to strength in resistance-trained individuals?

AIM: Previous work in non-resistance-trained individuals has found that an increase in muscle size has no additive effect on changes in strength. However, it is thought that muscle growth is of increased importance for resistance-trained individuals. PURPOSE: Experiment 1: To examine changes in muscle thickness (MT) and one repetition maximum (1RM) strength following 8 weeks of bi-weekly 1RM practice or traditional training. Experiment 2: To determine whether increasing muscle size increases strength potential when followed by 4 weeks of 1RM training. METHODS: Participants performed biceps curls for 8 weeks (Experiment 1). One arm performed 4 sets of as many repetitions as possible with approximately 70% of 1RM (TRAD), and the other arm performed a single 1RM. For experiment 2, both arms trained for muscle size and strength. RESULTS: Experiment 1 (n = 25): for MT, the posterior probabilities favoured the hypothesis that MT changed more in the TRAD condition [mean difference: 50% site 0.15 (-0.09, 0.21) cm; 60% site 0.14 (0.06, 0.23) cm; 70% site 0.17 (0.10, 0.23) cm]. For 1RM strength, each condition changed equivalently. Experiment 2 (n = 18): for MT, the posterior probabilities favoured the hypothesis that MT changed similarly between conditions following a 4-week strength phase. For changes in 1RM strength, the evidence favoured neither hypothesis (i.e. null vs. alternative). Of note, the mean difference between conditions was small [0.72 (4.3) kg]. CONCLUSIONS: 1RM training produces similar increases in strength as traditional training. Experiment 2 suggests that increases in muscle mass may not increase the 'potential' for strength gain.

An examination of changes in muscle thickness, isometric strength and body water throughout the menstrual cycle.

PURPOSE: The purpose of this study was to examine the changes in muscle size and strength throughout the menstrual cycle in females and to compare these values to a control group of time-matched males. METHODS: 12 males and 16 females visited the laboratory on four occasions. Measures of muscle thickness (MTH), isometric strength and body water were taken during the menstrual phase, ovulation phase and luteal phase of the menstrual cycle. Males scheduled their visits based on a mock menstrual cycle. In addition, participants were asked to complete 4 sets of biceps curls to volitional failure in one arm to examine swelling during each visit. RESULTS: For MTH there was no interaction (p = .73); however, there was a main effect for sex with males having higher MTH values compared to females [4.07 (0.67) versus. 2.73 (0.42) cm, (p < .001)] at all time points. For changes in MTH (swelling) there was no interaction (p = .28). However, there was a main effect for sex, with males demonstrating greater changes in MTH compared to females [0.53(0.11) versus. 0.40 (0.10) cm, (p < .001)]. Similarly, for total body water, there was no interaction (p = .66). However, males had greater total body water compared to females [49.6 (6.8) versus. 32.3(3.9) kg, p < .001)] at all time points. Finally, for isometric strength, there was no interaction (p = .23). However, there was a main effect for sex. Males had higher isometric strength values compared to females [285 (42) versus. 156(36) N (p < .001)]. CONCLUSIONS: Phase of the menstrual cycle does not appear to influence MTH, isometric strength or total body water.

An examination of changes in skeletal muscle thickness, echo intensity, strength and soreness following resistance exercise.

It is suggested that changes in echo intensity (EI) measured through ultrasound can detect muscle swelling. However, changes in EI have never been examined relative to a non-exercise control following naïve exposure to exercise. PURPOSE: Examine the changes in muscle thickness (MT), EI and isometric strength (ISO) before, immediately after, and 24, and 48 hr following biceps curls. METHODS: Twenty-seven non-resistance-trained individuals visited the laboratory four times. During visit 1, paperwork was completed and strength was measured. During visit 2, MT and ISO were measured before four sets of curls. Additional measures were taken immediately after exercise, as well as 24 and 48 hr post. Results are displayed as means (SD). RESULTS: For MT, there was an interaction (p < .001). For the experimental condition, MT increased from pre [2.88(0.64) cm] to post [3.27(0.67) cm] and remained elevated 48 hr post. There were no changes for MT in the control arm. In the experimental arm, EI increased from pre [22.9(9.6) AU] to post [29.1(12.3) AU] exercise and returned to baseline by 24 hr. For the control condition, EI was different between pre [24.8(10.2) AU] and 48 hr [21.5(10.7) AU]. The change in EI in the experimental condition was greater than the control condition immediately post (p = .039) and at 48 hr (p = .016). For ISO, there was an interaction (p < .001). In the experimental condition, ISO decreased from pre [40.6(14.7) Nm)] to post [24.8(9.4) Nm] and remained depressed. CONCLUSIONS: Exercise produced a swelling response, which was elevated 48 hr post. Despite a sustained increase in MT, EI was only elevated immediately post exercise.

Cardiovascular and Muscular Response to NO LOAD Exercise with Blood Flow Restriction.

Changes in muscle thickness (MT), isometric torque, and arterial occlusion pressure (AOP) were examined following four sets of twenty unilateral elbow flexion exercise. Participants performed four sets of maximal voluntary contractions with no external load throughout a full range of motion of a bicep curl with and without the application of blood flow restriction (BFR). For torque there was an interaction (p = 0.012). The BFR condition had lower torque following exercise (56.07 ± 17.78 Nm) compared to the control condition (58.67 ± 19.06 Nm). For MT, there was a main effect for time (p < 0.001). MT increased from pre (3.52 ± .78cm) to post (3.68 ± 81cm) exercise and remained increased above baseline 15 min post-exercise. For AOP, there was an interaction (p = 0.027). The change in AOP was greater in the BFR condition (16.6 ± 13.42mmHg) compared to the control (11.1 ± 11.84 mmHg). NO LOAD exercise with BFR let to greater reductions in torque and an exaggerated cardiovascular response compared to exercise alone. There were no differences in swelling. These results suggest that the application of BFR to NO LOAD exercise may result in greater fatigue.

A comparison of acute changes in muscle thickness between A-mode and B-mode ultrasound.

OBJECTIVE: The purpose of this study was to compare acute changes in muscle thickness (MT) between A-mode and B-mode ultrasound before and after four sets of biceps curls. APPROACH: Participants visited the laboratory on two separate occasions. The first visit consisted of paperwork and one repetition maximum (1RM) strength assessment. During the second visit, participants performed four sets of biceps curls to volitional failure using an exercise load equal to 70% of 1RM or a time-matched non-exercise control. MT measurements were taken before and immediately after exercise. MT measures were taken using both A-mode and B-mode ultrasound. MAIN RESULTS: Results are displayed as mean (SD). A total of 49 resistance-trained men (n = 24) and women (n = 25) completed the study. There was no group (experimental versus control) by mode (A-mode versus B-mode) by time interaction (p  = 0.442). However, there was a group (experimental versus control) × time (pre versus post) interaction (p  < 0.001). Muscle thickness increased from pre (3.61 (0.86) cm) to post exercise (4.06 (0.92) cm) in the experimental group (p  < 0.001). However, there was no change from pre (3.46 (0.78) cm) to post (3.48 (0.78) cm) in the time-matched control group (p  = 0.237). There was a main effect for ultrasound mode (A-mode versus B-mode) (p  < 0.001). Muscle thickness values as measured by A-mode ultrasound were lower than those measured by B-mode ultrasound pre (A-mode = 3.43 (0.79) cm versus B-mode = 3.63 (0.84) cm) and post (A-mode = 3.67 (0.87) cm versus B-mode = 3.83 (0.91) cm) intervention. SIGNIFICANCE: MT measurements taken using A-mode ultrasound are lower than those of B-mode ultrasound. Despite this difference, it appears A-mode can detect similar acute changes in MT following resistance exercise when compared to B-mode ultrasound. These results suggest that A-mode ultrasound can serve as a useful tool when examining acute changes in MT.

Can changes in echo intensity be used to detect the presence of acute muscle swelling?

OBJECTIVE: The purpose of this study was to examine acute changes in muscle thickness (MTH) and echo-intensity (EI), following four sets of biceps curls, when it is known that the change in MTH is due entirely to swelling. APPROACH: Forty-nine resistance-trained men and women participated in this study. Individuals in the experimental group (n = 23) visited the lab on two separate occasions. During the first visit, paperwork and one repetition maximum (1RM) strength were measured. During the second visit (3-5 d after visit 1), individuals performed four sets of biceps curls to failure using 70% of their 1RM. MTH and EI measurements were taken before and immediately following exercise using B-mode ultrasound. The ultrasound probe was equipped with a level to minimize the influence of probe tilt on the EI measurement. A time-matched control group (n = 26) was included to account for measurement error for both MTH and EI. Results are presented as means (95% CI). MAIN RESULTS: For MTH there was a group (Experimental versus Control) by time (Pre-Post) interaction (p  < 0.001). MTH increased in the experimental group (mean value change = 0.44 (0.33-0.54) cm), but not in the control group (mean value change = -0.015 (-0.03-0.01) cm). For EI, there was no group by time interaction (p  =.074). In addition, there were no main effects for group (p  = 0.254) or time (p  = 0.314). The mean difference in the change in EI between groups was -2.99 (-6.25-3.03) arbitrary units. SIGNIFICANCE: EI cannot be used to detect exercise induced changes in muscle thickness.