Institute of Exercise Physiology & Wellness, University of ...

Adam J. Wells, David H. Fukuda, Adam M. Gonzalez, Adam R. Jajtner, Jeremy R. Townsend, Gerald T. Mangine, Maren S. Fragala, Jeffrey R. Stout, FACSM, and Jay R. Hoffman, FACSM.

Institute of Exercise Physiology & Wellness, University of Central Florida, Orlando, FL, USA,

ABSTRACT

Changes in strength can be attributed in part to adaptation of a number of architectural parameters within muscle. Adaptation may also be specific to certain regions of the muscle. PURPOSE: To compare changes in strength with changes in vastus lateralis (VL) muscle architecture at two transverse landmarks (VL0 and VL5) during off-season conditioning. METHODS: Twenty-three female competitive athletes (19.7 ? 1.0 y; 1.71 ? 0.08 m; 64.6 ? 8.9 kg) participated in a 15-week off-season training program. Testing was conducted at the beginning (PRE) and end (POST) of training. Each visit consisted of maximal strength (1-repetition maximum [1RM] barbell squat test) and muscle architecture measures. Cross sectional area, echo intensity, muscle thickness (MT), pennation angle (PA), and fascicle length (FL) of the VL were measured via ultrasonography of the athlete's self-reported dominant leg. VL0 was defined as the point of intersection between the VL and 50% of the straight line distance between the greater trochanter and the lateral epicondyle of the femur. VL5 was sampled at a point 5cm medial of VL0. Comparisons between VL0 and VL5 were made using an independent t-test. Changes in muscle architecture and strength measures were analyzed using magnitude based inferences derived from the p-value of dependent t-tests. Relationships between changes in VL architecture and strength were examined using Pearson correlation coefficients, which were further analyzed to determine the magnitude of effect. RESULTS: Significant increases in 1RM squat strength (3.7 ? 2.4 kg, p = 0.004), FL at VL0 (0.4 ? 0.31 cm, p = 0.036), and MT at VL5 (0.19 ? 0.073 cm, p < 0.001) were observed from PRE to POST. Changes in MT at VL5 were significantly greater than changes in MT at VL0 (p = 0.006). A possibly greater increase in PA at VL5 was observed compared to VL0. Changes in 1RM squat strength were significantly correlated with changes in MT at VL0 (r = 0.561, p = 0.037). Analysis of the magnitude of correlation coefficient relationships revealed a likely positive moderate correlation between changes in 1RM squat strength and changes in FL at VL0. CONCLUSION: Transverse changes in VL muscle architecture appear to occur in a non-homogeneous fashion. Changes in 1RM strength showed significant positive correlations with changes in muscle architecture at VL0 only.

INTRODUCTION

? Muscle architecture varies across both individual muscles and muscle groups according to the tissue's functional role with distinct architectural structures conferring specific contractile properties 1.

? In addition, muscle demonstrates a high degree of plasticity in regards to its configuration, resulting from both contractile and metabolic functional demands 2.

? Changes in strength may be attributed, in part, to the simultaneous adaptation of a number of interrelated architectural parameters 3. Further, adaptations may also be specific to certain regions of the muscle 4-6.

? Variations in transverse point of measure landmarks may have a significant effect on both the expression of the structure-function relationship and observed adaptation.

PURPOSE

? To compare changes in the muscle architecture of two commonly utilized point of measure landmarks occurring transversely within the vastus lateralis (VL), in order to assess whether architectural adaptation occurs homogeneously across the VL.

? To correlate changes in muscle architecture of VL at each anatomical landmark, to changes in maximal strength following the completion of an off-season conditioning program.

METHODS

? Twenty-three competitive female athletes (Age: 19.7 ? 1.0 years; height: 1.71 ? 0.08 m; body mass: 64.6 ? 8.9 kg) participated in this study. Measures of reaction time, cognition and mood state were assessed immediately pre and post workout at T1 and T2.

? Participants reported to the Human Performance Laboratory (HPL) for testing at the beginning (PRE) and end (POST) of the 15-week off-season conditioning program. PRE and POST testing consisted of the same assessment protocol.

? Each visit consisted of anthropometric measures of height and body mass, followed by musculoskeletal ultrasound of the VL of the dominant leg.

? Participants also completed a barbell squat 1-repetition maximum (1-RM) test.

METHODS CONT.

Ultrasound Assessment ? Measurements of muscle thickness (MT), cross sectional area (CSA), pennation

angle (PA) and echo intensity (EI) were collected via non-invasive ultrasonography. ? Fascicle length (FL) was estimated using the average of three images for MT and

PA at VL0 and VL5. FL was estimated using the following equation 7-9. Fascicle length = MT SIN (PA)-1 ? All measures were collected on the VL of the participant's self-reported dominant leg and were performed by the same technician.

Figure 1. Representative image or architectural landmarks. VL0 was determined by the point of intersection between the VL and 50% of the straight line distance between the greater trochanter and the lateral epicondyle of the femur. VL5 was sampled at a point 5cm medial of VL0, on a line perpendicular to the muscle tissue toward the anterior side of the body.

Post-Season Workout

Table 1. Participants engaged in a 15-week linear periodized resistance training program consisting of a weekly 4-day per week, split routine.

All exercises performed to a repetition maximum range. * Day 2 only; ^ = Day 4 only; 1, = 1 warm-up set Statistical Analysis ? All differences and relationships were assessed using magnitude based inferences, calculated from 90% confidence intervals 10. ? Comparisons between VL0 and VL5 were analyzed using the p value from independent t-test, while changes in musculoskeletal architecture and performance measures from PRE to POST were analyzed using the p value from dependent t-test to determine a mechanistic inference. ? Qualitative inferences were based upon the chances that the true magnitude of the effect at POST- off-season were substantially greater or smaller than baseline values (PRE), and were assessed as: 99% almost certainly greater 11. ? If there was a greater than 5% chance that the true value was both greater and smaller, the effect was considered mechanistically unclear. ? The smallest non-trivial change, or smallest worthwhile change, was set at 20% of the grand standard deviation for all PRE-values 11. ? The relationship between changes in musculoskeletal architecture and changes in strength were examined using Pearson correlation coefficients. Correlation coefficients were further analyzed using a published spreadsheet to determine the magnitude of effect 12.

RESULTS

? Significant increases in 1RM squat strength (3.7 ? 2.4 Kg, p = 0.004) were observed from PRE to POST.

? A likely greater FL at VL0 (80.1%) was observed from PRE to POST. ? A very likely greater MT at VL5 (99.4%), likely greater FL at VL5 (81.2%), and a

possibly greater PA at VL5 (49.5%) were observed from PRE to POST. ? Changes in 1-RM squat strength showed likely positive correlations with MT and FL

at VL0 at the 0.3 threshold (85.9% and 79.1% respectively).

Table 2. PRE-POST changes in muscle architecture ? VL0 vs. VL5.

Muscle Architecture

VL0

VL5

Percent p Pos Triv Neg

Interpretation

MT

0.04 ? 0.16

0.18 ? 0.18

.006 98.1 1.8 0.0 Very Likely Greater

PA

- 0.26 ? 1.47

0.64 ? 2.79

.183 74.7 22.9 2.4

Possibly Greater

FL

0.40 ? 0.84

0.46 ? 1.29

.795 31.7 48.4 20.0

Unclear

= PRE-POST changes; n = sample size; p = Significance; Pos = % Positive change; Triv = % Trivial change; Neg = % Negative change; MT = Muscle Thickness (cm); PA = Pennation Angle (?); FL = Fascicle Length (cm); VL0 = Intersection of VL and 50% of the straight line distance between the greater trochanter & lateral epicondyle of the femur; VL5 = 5cm medial of VL0. Comparisons between VL0 and VL5 were analyzed using the p value from independent t-test.

PRE-POST Changes in Muscle Thickness

3

+ 2.88%

+ 9.55%

2.5

Muscle Thickness (cm)

2

1.5

1

0.5

1.39 0

MT PRE

1.43 MT POST

1.99 MT PRE

2.18 MT POST

VL0

VL5

Landmark

Figure 2: PRE-POST changes in muscle thickness ? VL0 vs. VL5; = Significant change from PRE (p < 0.01); = Significantly greater change than VL0

? = Possibly Greater = Likely Greater = Very Likely Greater

?

Figure 3: Magnitude based inferences for architectural change [mean (POST-PRE) ? 90% confidence limits] at VL0 and VL5 relative to the smallest worthwhile change (SWC). The SWC (trivial zone) was set at 20% of the grand standard deviation for all PRE-values. For figure clarity, changes were represented as a factor of the SWC in order to compare values with differing units and were determined by dividing the mean and 90% confidence limits of each parameter by its corresponding SWC value.

RESULTS CONT.

Table 3. Correlations between changes in muscle architecture and changes in 1-RM Strength

Percent

Thr

r

p

Pos

Triv

Neg

Interpretation

Ultrasound

VL

VL CSA

.1

.303 .293 76.0 15.5

8.5

Unclear

VL EI

.1

.176 .547 60.1 22.0 17.8

Unclear

VL0

VL MT

.3

.561 .037 85.9 14.0

0.1

Likely Positive

VL PA

.1

.031 .920 41.3 24.8 33.9

Unclear

VL FL

.3

.503 .080 79.1 20.7

0.2

Likely Positive

VL5

VL MT

.1

- .093 .753 26.0 24.9 49.1

Unclear

VL PA

.1

- .043 .885 31.7 25.8 42.5

Unclear

VL FL

.1

- .055 .852 30.3 25.7 44.0

Unclear

1-RM = 1 Repetition Maximum; = PRE-POST changes; n = sample size; Thr = Threshold; r = Pearson Correlation; p = significance; Pos = % positive correlation; Triv = % Trivial correlation; Neg = % Negative Correlation; VL = Vastus Lateralis; CSA = Cross-Sectional Area; EI = Echo Intensity; MT = Muscle Thickness; PA = Pennation Angle; FL = Fascicle Length;

Figure 2. Comparative changes in muscle thickness (MT) and pennation angle (PA) at VL0 and VL5 from PRE to POST training.

MT and PA were quantified within still images captured longitudinally in the transverse plane.

MT was determined as the distance between the inferior border of the superficial aponeurosis and the superior border of the deep aponeurosis at VL0 and VL5.

PA was determined as the intersection of the superficial

border of the deep aponeurosis with a visible fascicle at

VL0 and VL5.

SUMMARY & CONCLUSIONS

? Changes in muscle architecture measured transversely within the VL appear to occur in a non-homogeneous fashion.

? Changes in strength showed moderate positive correlations with FL and MT at VL0 only.

? Measures of cross-sectional area may not fully represent the dynamic adaptation of muscle architecture following resistance exercise. Therefore, it is recommended that measures of muscle thickness be assessed in conjunction with CSA.

? These findings provide a rationale for variable dependent selection of VL0 and VL5 landmarks when assessing muscle morphology.

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