Introduction: Investigating longitudinal changes in an athlete’s muscle architecture helps coaches recognize physiological underpinnings associated with performance. Typically during a competitive season athletes sports performance increases, while standard descriptions of fitness such as maximal strength remain at a baseline or even decline. This leaves coaches to hypothesize why their athletes’ standard fitness measurements have declined but their sports performance has improved. Investigating the changes in muscle architecture can help determine the mechanisms which evoke performance improvements. Measurements in muscle architecture are performed via ultrasound and include: muscle thickness, pennation angle, and fascicle length. It has been suggested that these measurements account for more of the variance in muscle strength and velocity than intrinsic properties. Additionally, these physiologic variables are adaptable depending on an athlete’s training and competitive season. Despite the sound theoretical background for tracking athletes muscle architecture changes, very little longitudinal research has been conducted.
Softball is a sport which involves many competitions with little time between games. This restricts an athletes time for in-season strength conditioning. In order to optimize an athlete’s in-season program, coaches need to understand the changes which occur in muscle architecture during the competitive season. Understanding the changes in muscle architecture can allow coaches to make better training choices to further promote or avert particular adaptations. Therefore, the purpose of this study was to examine the relationship between muscle architecture and changes in strength, speed, and change of direction in elite softball players during the competitive season.
Purpose: The purpose of this study was to examine the relationship between muscle architecture and changes in strength, speed, and change of direction in elite softball players during the competitive season.
Subjects: The study consisted of 10 elite female softball players with an average age of 18.1 ± 1.6 years, average height of 166.48 ± 8.9 cm, and weight of 72.43 ± 10.82 kg. The subjects had a minimum of 1 year of supervised resistance and sport specific training experience. No other descriptions were provided.
Procedures and Methods: The athletes were followed during their normal training program for a season. The training included conditioning and speed sessions in addition to resistance training. Softball practice also occurred 2-3 times per week. The first tournament for the players occurred at week 7 and the peak tournament was at week 22. Testing was done preseason, midseason, and postseason. Position specific training volume was not accounted for, as each position completes different drills. For example, it is obvious a second baseman is going to perform more change of direction drills during practice than a first baseman or catcher. Each subject performed identical lower-body lifts and speed conditioning sessions. Rotator cuff and core work was dependent on positional needs. Due to these training differences, measurements included lower-body adaptations only. The resistance training program consisted of lifts with weights approximately 80-100% of the athletes maximum. Ballistic jump squat (JS) was performed at 30% maximum. One lifting session was considered a light-moderate day, where intensity was lower and the sets were easily completed (80-90% RM). The second day was a heavy day where athletes lifted at higher intensities (≥ 90% RM). The training consisted of 4 mesocyles: 2 strength and 2 power blocks. The total time from pretesting to posttesting was 20 weeks, the final competition occurred at week 22. One week of active recovery was provided between blocks and midseason testing occurred at week 9. The total time in each block was as follows: strength I (4 weeks), strength II (3 weeks), power I (4 weeks), power II (3 weeks). Exercises for each block were slightly modified for each block. For strength block I, exercises included the back squat, deadlift, and split squat. For strength block II, the power clean was added to this list. For power block I, the hang clean, jump squat, and back squat were chosen. Power block II used the same exercises, but at a reduced volume.
Strength was assessed by using the 3-repetition maximum (3RM) back squat. Subjects attempted to complete 3 RM of their estimated maximum from previous testing. If successful, additional weight was added and a 3-5 minute rest period was implemented. This process continued until failure occurred on the 4th repetition. Jump squat testing was done on a force plate holding either a fiber glass pole (JSBM) or a 24.5 kg bar (JSBar). Peak force (PF), peak velocity (PV), and peak power (PP) were derived from these jumps. Subjects were given 1 minute of rest between attempts. Attempts were performed at body mass (JSBM), body mass + Bar (24.5 kg) (JSBar), body mass + 40% of 1RM (JS40), body mass + 60% of 1RM (JS60), and body mass + 80% of 1RM (JS80). The intraclass correlation coefficient for JSBM was ≥ 0.96. For JSbar, JS40, JS60, and JS80 reliability was as follows: ICC PF 0.88–0.98, ICC PV 0.87–0.94, and ICC PP 0.93–0.98
Sprint times were recorded using dual beam timing lights with an accuracy of 1/100th of a second. Home to first and home to second were recorded. Each subject completed each sprint twice and the best time was recorded. Change of direction was assessed via the 505 change of direction test (505). The time from the 10 m gait to the 15 m cones and back to the 10 m gait was recorded. Each athlete performed each pivot once with the left and once with the right foot (505D, 505 ND for dominant and non-dominant foot). The best time was recorded. The ICC was ICC ≥ 0.93 for this test. Aerobic capacity was assessed via the multi-staged shuttle test, and VO2 max was estimated from the time to complete this test.
Ultrasound was used to measure muscle architecture. Sagittal plane images were taken of the vastus lateralis (VL) at 50% of the distance from the greater trochanter to the lateral epicondyle of the femur. The images were taken of the dominant side. Two images were taken each session and subjects were placed with the knee and hip flexed to 90 degrees. Muscle thickness was measured as the distance from the subcutaneous adipose tissue-muscle interface and the muscle-bone interface. The average of 3 measures was used. Fasicle length was estimated using FL=MT (sin θp)−1 . The ICC for MT was 0.93-0.98 and for FL 0.88-0.95.
Results: Significant increases were found for squat absolute 1RM and relative squat 1RM from pre to posttraining (p=0.01, p=0.002). Small to moderate effect sizes were also found for both from pre to posttraining (ES=0.73 for absolute and ES=0.48 for relative). Significant improvements in strength were also noted from pre to midseason (p=0.002, ES=0.65 for absolute and p<0.001, ES=0.39 for relative). Significant decreases were noted for the 505ND (p = 0.03, ES = −0.81) but not for 505D (ES = −0.43). Significant decreases were also found for 2B sprint time from pre to post (p = 0.007, ES = −0.53). All other measures were nonsignificant (aerobic capacity, 1B sprint time).
Measurements of muscle architecture were not significant at any of the time periods. There was a moderate magnitude increase from pre to post (ES=0.80) and mid to post (ES=0.77) for fascicle length. A small magnitude decrease was observed in pennation angle from pre to posttesting (ES=-0.27).
Significant and large magnitude increases occurred in PV and relative PP for all JS conditions from pre to posttesting and pre to midtesting. Significant changes with moderate magnitude of increase occurred in relative PF from pre to posttesting for all JS except JSBM (no significance values provided).
Several relationships were found between muscle architecture changes and performance changes. The percentage change in VL MT displayed near significant and very large magnitude with % change in 1B sprint (r= -0.80, p=0.06) and a large but nonsignificant relationship to 2B sprint (r=-0.55, p=0.20) and relative 1RM strength (r= 0.57, p = 0.18). The % change in VL FL was of large magnitude with 1B sprint (r= -0.53, p=0.28) and VL pennation angle (r=-0.58, p=0.13). There was a very large and significant relationship between VL FL and 2B sprint time (r= -0.84, p=0.02) and VL FL and VL MT (r= 0.72, p=0.04). There was a very large relationship between % change in relative 1 RM and 505 D (r= -0.70, p=0.12) and a large relationship between % change in relative 1 Rm and 505 ND (r= -0.512, p=0.30).
Discussion and Conclusions: There were two main findings from this study. First, elite female athletes are able to maintain and even increase their levels of strength, power, and performance during a competitive season. Second, the percent change in muscle architecture has moderate to very large relationships with the percent change in certain performance variables. These findings demonstrated a strong relationship between fascicle length and sprint time. The longer the muscle’s fascicle length, the lower the sprint time (negative relationship). This is consistent with other research findings concerning sprint times and fascicle length. During this study most of the changes in architecture occurred during the power phases of training. This is mostly likely due to the changes in training, from a strength emphasis to a high velocity emphasis. It is possible high velocity training stimulates increases in fascicle length and reductions in pennation angle. Importantly, it remains unknown why most of the performance increases occurred from pre to midtesting, but most muscle architectural changes occurred from mid to posttesting. Also noted was a significant and very large correlation between muscle thickness and sprint times. This demonstrates that accrual of muscle thickness positively influences sprint times. Furthermore, these findings were consistent with strength gains, which also demonstrated a positive association with muscle thickness. One interesting detail found was muscle thickness explained 64% of the variance in 1B sprint time while fascicle length accounted for 69.7% of the variance for 2B sprint time. It appears 1B sprint time may be more related to strength and acceleration while 2B may be more related to maximal speed. Another important finding was increasing relative strength positively influences change of direction abilities. It can be deducted from this data that the stronger an athlete is for their given body weight, the easier it is for them to alter their direction. In conclusion, it appears an in-season periodized strength program can enhance performance measurements in elite softball players. A time-lag effect can be expected in muscle architecture when switching from a strength based program to a power based program in this population. These adaptations may allow the athletes to continue to enhance their performance despite reductions in overall training volume. Limitations of this study include a small sample size with the inclusion of only one sex.
My Thoughts: I thought this was a really interesting study because of the length and realistic set-up. They allowed each athlete a certain amount of flexibility in their training. Meaning a shortstop got to train as a shortstop while a catcher got to train as a catcher. I don’t think it would be realistic to make each train or practice using the same drills. I thought the results matched up pretty well with the overall literature and practical thoughts of a coach. Larger muscles help athletes run faster. Increasing fascicle lengths also demonstrated performance improvements. One significant limitation in this study was the face the authors had to use the quads as their testing muscles. This limited the performance measurements to mainly running, agility, and lower body explosive testing. It would be of more benefit if the authors also included more sport specific testing, including lateral to medial jumps, throwing velocity, and bat speed. These are much more relevant to softball than vertical jumps and even maximal running to second base (which is only performed every so often). Future insights should include these measures, larger samples, and if possible more muscle groups.
Nimphius, S., McGuigan, M. R., & Newton, R. U. (2012). Changes in Muscle Architecture and Performance During a Competitive Season in Female Softball Players. Journal of Strength and Conditioning Research, 26(10), 2655-2666. doi:10.1519/jsc.0b013e318269f81e
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