1. Relationship between Isometric Force Characteristics and Hitting Performance in NCAA Division 1 Baseball Players
W. G. Hornsby III, C. A. Bailey, C. Y. Chiang, B.J. Andersen, J.A. Gentles, B. D. Johnston, and M.H. Stone
KLSS /Center of Excellence for Sport Science and Coach Education, Sports Science Laboratory,
East Tennessee State University, Johnson City, TN
Introduction
Discussion:
Statistical Analysis
The emphasis on training strength and explosive strength in regards to baseball preparation has increased rapidly over the last 2 decades. As evidence of this players have risked suspension and a damaged public perception by taking anabolic, strength inducing androgens (Mitchell , 2007; Shermer, 2008).
Descriptive statistics (tables 1 and 2) were expressed as means with standard deviations. SPSS statistical analysis software version 19 was used to determine Pearson correlation coefficients. Alpha levels were set at 0.05 and 0.01 to determine statistical significance amongst all variables.
Baseball performance is a multifaceted problem however; strength characteristics (e.g. rate of force development, force production at early time periods) are a key component. The neuromuscular system’s ability to produce force is defined as strength (Stone et al., 2003).  From a physics standpoint, force is a vector quantity, has both a magnitude and direction (Stone et al., 2003).  Sokolov (1974) explains that an athlete’s expression of strength is referred to as technique. Thus, baseball players rely on producing forces in optimal directions throughout their pitching, hitting, fielding, sequences. To improve baseball performance players must either enhance the direction(s) of the forces generated or the magnitude, or both. Increased strength can result in greater directional forces and allows baseball players to exhibit greater bat swing velocities (Syzmanski 2010), and greater throwing velocities (Pottegier, 1992a; Pottegier, 1992b; Syzmanski 2010).
The time allowed to perfrom baseball movements such as swinging a bat, or throwing a ball is less than the time necessary to produce maximal force (peak force) (Adair, 1990; Blazevzich, 2008). The ability to produce force rapidly has been shown to be crucial for sport performance in strength power athletes (Stone et al., 2003). Rate of force development is quantified as the rate of change in force divided by change in time (Stone, Stone & Sands, 2007), thus the more rapid the increase in muscle activation by the nervous system the greater the RFD. Faster muscle force production results in greater force production at the early phase of a maximal or near maximal muscle contraction. Schmedtbleicher (1992) explains that RFD is associated with the ability to accelerate objects (e.g. a bat, a ball, one’s own body mass). Therefore, greater explosive strength is associated with higher acceleration capabilities. Stronger athletes typically possess greater RFD (Stone et al., 2003).
Establishing relationships between biomotor variables and performance can lend valuable insight for coaches and strength and conditioning coaches. Relationships help identify what variables to focus on within a baseball players training prescription. Based on the correlational data presented in the present study increasing RFD, force at 50ms, force at 90ms, and force at 250ms can potentially enhance hitting performance. Furthermore, increasing maximum strength may enhance these variables.
Strength
Table 1. Descriptive Data for Isometric Clean Grip Mid-Thigh Pulls (N= 25).
Table 2. Descriptive Data for Hitting Performance (N=25).
Methods
Isometric Data
Mean
Std. Deviation
Force at 50ms
Force at 90ms
Force at 250ms
Peak Force
IPFa
Hitting Data
Mean
Std. Deviation HR
9.64
7.059
Batting Avg.
.31952
Slugging %
.53456
Doubles
13.96
5.526
NCAA Baseball players from the seasons of 2009, 2010, and 2011 participated in this descriptive, hypothesis generating study. Each year, 30 to 45 days prior to the start of the season the players underwent isometric strength testing as part of an on-going athlete monitoring program integrated into their training program. Isometric force data was correlated with their hitting data in an effort to establish relationships between measures of strength and hitting performance.
Subjects
Table 3. Correlations between isometric force data and hitting data. (*=0.05, **=0.01)
Variable
RFD
50ms
90ms
250ms HR
.633**
.586**
.640**
.605**
Batting Avg.
.546**
.261
.420*
.415*
Slugging %
.609**
.548**
.624**
.570**
Doubles
.583**
.446*
.574**
.491*
25 NCAA division 1 baseball players (body mass = 88.0kg kg and height = 146.8cm cm) from the spring baseball seasons of 2009, 2010, and To be included in the data sample each player had to have a minimum of 100 at bats across a spring NCAA season.
Explosive Strength
Testing Procedure
Maximum strength was measured using an isometric mid-thigh clean pull, which was performed on a 0.91m x 0.91m force plate (Rice Lake, WI; sampling rate of 1000 Hz) in a custom-designed power rack. Prior to performing the isometric pull athletes followed a standard warm-up consisting of 25 jumping jacks followed by 3x5 mid-thigh pulls wih 60kg after one set with the bar. The apparatus and standardized pulling position was established based upon previously published data (Haff et al., 1997). The athletes’ hands were attached to the bar using weightlifting straps and standard athletic tape to prevent their hands from moving to ensure that the athletes could perform a maximal pull regardless of hand strength. This test was chosen because it correlates very strongly with a number of other performance characteristics and all athletes were familiar with the pulling position (Haff et al., 1997).
Each athlete was given two practice trials at submaximal efforts (50% and 75% effort). Following the practice trials, athletes performed 2 maximum effort trials with approximately 1 minute rest between pulls. Athletes were explicitly instructed to perform the pull “as hard and fast as possible”. The trials were then averaged for analysis
Customized Labview software (National Instruments Co., Austin, TX) was used to determine the isometric peak force (IPF), instantaneous forces at 50, 90, and 250 ms, and isometric rate of force development (RFD) during the first 200ms of each pull. When appropriate IPF was allometrically scaled (IPFa) to obviate differences in body mass amongst players. Previous testing in our lab (n > 200) has consistently produced a test-retest reliability of: PFs, ICCα ≥ 0.98, and rate of force development, ICCα ≥ 0.95.
Table 4. Correlations between isometric force variables. (*=0.05, **=0.01)
Variable
RFD
50ms
90ms
250ms
Peak Force
.796**
.598**
.709**
.898**
IPFa
.401*
.559**
.753**
Practical Implications
Graph 1. Relationship between HRs and RFD.
References
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Home R u n s A) B)
Rate of Force Development
Results
Table 3 shows correlations between isometric force data and hitting data while table 4 shows correlations amongst isometric force variables. These data demonstrate several strong (r= ) and moderate (r= ) correlations. For example, rate of force development was strongly correlated with home runs, batting average, slugging percentage, and doubles. Force production at early time periods (force at 50ms, force at 90ms, and force at 250ms) was strongly and moderately correlated with home runs, batting average, slugging percentage, and doubles at all force-time periods measured except for batting average and force at 50ms.
IPF was strongly correlated with measures of explosive strength (RFD) and forces at 50ms, 90ms, and 250ms. IPFa was strongly correlated with RFD and forces at 90ms, and 250ms.
Note: A) Schematic Isometric mid-thigh clean pulls; B) Photographic representation of Isometric mid-thigh clean pulls.