# A New Method for Evaluating Pelvic and Trunk Rotational Pitching Mechanics: From Qualitative to Quantitative Approaches

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Participants

#### 2.2. Procedures

#### 2.3. Parameters

#### 2.3.1. Parameters on the Timing of Events

#### 2.3.2. Parameters of the Angle at the Time of Events

#### 2.3.3. Parameters of Trunk–Pelvis Separation at the Time of Events

#### 2.3.4. Parameters Associated with Special Time Events and Intervals

#### 2.3.5. Parameters That Are Important during the Stride Phase

#### 2.4. Statistical Analyses

## 3. Results

## 4. Discussion

#### 4.1. Three Novel Phases of Pelvic and Trunk Rotation during Pitching

#### 4.1.1. Phase1

#### 4.1.2. Phase2

#### 4.1.3. Phase3

#### 4.2. Characteristics of Pattern1 (Closed Hip-to-Shoulder Separation)

- (1)
- They rotate their trunks backwards following the pelvises in Phase1 (Figure 4B).
- (2)
- They commence rotation of their pelvises (backwards and then forwards) earlier in Phase1 (Figure 4A).
- (3)
- (4)
- They do not rotate their trunks backwards in Phase2 just before foot contact while pitchers in Pattern2 rotate their trunks backwards (Figure 4B).

#### 4.3. Evaluation of Pelvic and Trunk Rotational Mechanics Using “PAoFC” Accompanied by “TPSoFC”

#### 4.4. Limitations

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**(

**A**) Closed pattern of “hip-to-shoulder separation”; (

**B**) Open pattern of “hip-to-shoulder separation”.

**Figure 2.**A schematic diagram comparing Pattern1 and Pattern2 viewing in the transverse plane at different time ratios. The kinematic definition of pelvic and trunk axial rotation is in relation to global coordinate system. In the transverse plane, rotation towards the home plate is defined as 0°, whereas that towards third base is defined as −90°. MKU = maximum-knee-up; FC = foot contact; MER = maximum -shoulder-external-rotation; BR = ball-release.

**Figure 3.**(

**A**) Curves of mean rotational angle of pelvis and trunk related to time ratio from MKU to MIR of Pattern1. It shows two special time events: AC1 and AC2, as well as three novel phases. (

**B**) Curves of mean rotational angle of pelvis and trunk related to time ratio from MKU to MIR of Pattern2. AC1 = time of first pelvic and trunk angle crossing; AC2 = time of second pelvic and trunk angle crossing; BR = ball-release; FC = foot contact; MIR = maximum -shoulder-internal-rotation; MKU = maximum-knee-up.

**Figure 4.**(

**A**) Curves of mean pelvic angle of Pattern1 and Pattern2 related to time ratio from MKU to MIR. Arrow1 indicates that Pattern1 has an earlier MKU than Pattern2. Arrow2 indicates that Pattern1 has more of a leading pelvic rotational angle at the moment of foot contact (“PAoFC”) than Pattern2. (

**B**) Curves of mean trunk angle of Pattern1 and Pattern2 related to time ratio from MKU to MIR. Arrow1 indicates that Pattern1 has an earlier MKU than Pattern2. Pattern1 entails the backward rotation of the trunk in Phase1 (Arrow2), whereas Pattern2 does not feature this behavior. Pattern2 shows a turning-back of the trunk prior to foot contact in Phase2 (Arrow4), whereas Pattern1 does not present this tendency (Arrow3). (

**C**) Curves of mean trunk–pelvis separation (TPS) of Pattern1 and Pattern2 related to time ratio from MKU to MIR. Arrow1 indicates that Pattern1 has an earlier MKU and less of a TPS in Phase1 due to the backward rotation of the trunk. Pattern1 has an earlier AC1 (Arrow2) and later AC2 (Arrow4) than Pattern2. Pattern1 exhibits more of an absolute value of negative TPS at the moment of foot contact (“TPSoFC”) than Pattern2 (Arrow3). Note that Pattern1 and Pattern2 have different mean time ratios of MKU, MIR, AC1 and AC2 in (

**A**–

**C**). AC1 = time of first pelvic and trunk angle crossing; AC2 = time of second pelvic and trunk angle crossing; BR = ball-release; FC = foot contact; MIR = maximum-shoulder-internal-rotation; MKU = maximum-knee-up; P1 in parentheses = Pattern1; P2 in parentheses = Pattern2.

**Figure 5.**Four types of pelvic and trunk rotational pitching mechanics (viewing in the transverse plane). A “PAoFC” (Pelvic angle at the moment of foot contact) of −70° and “TPSoFC” (Trunk-pelvis separation at the moment of foot contact) of −25° were used for classification based on the result of the cut-off values from ROC (receiver operating characteristic). Type1 (proper mechanics) represents a leading “PAoFC” and is followed by the trunk with enough separation between the pelvis and trunk. Type2 (early trunk rotation) represents a leading “PAoFC” and is followed by the trunk with insufficient separation between the pelvis and trunk. Type3 (delayed pelvic rotation) represents a fallen behind “PAoFC” and is followed by the trunk with insufficient separation between the pelvis and trunk. Type4 (delayed pelvic rotation with trunk turning-back) represents a fallen behind “PAoFC” and is followed by the trunk with enough separation between the pelvis and trunk. Typically, the adequate separation of Type4 results from a turning-back of trunk rotation prior to foot contact. Types 2–4 are regarded as being characterized by “improper mechanics”.

Parameter | Pattern1 | Pattern2 | p Value |
---|---|---|---|

Hip-to-shoulder separation | Closed | Open | -- |

Participants | 18 | 12 | -- |

Age (years) | 23 ± 2 | 24 ± 3 | 0.070 |

Body height (cm) | 178 ± 4 | 182 ± 6 | 0.149 |

Body mass (kg) | 81 ± 8 | 84 ± 5 | 0.271 |

Abbreviation | Description |
---|---|

1. Parameters of timing of events | |

BRt-FCt (s) | Time interval between FC and BR |

MKUr (%) | Time ratio of MKU |

MERr (%) | Time ratio of MER |

MIRr (%) | Time ratio of MIR |

2. Parameters of angle at time events | |

TAoMKU (°) | Trunk angle at the moment of MKU |

TAoFC (°) | Trunk angle at the moment of FC |

TAoMER (°) | Trunk angle at the moment of MER |

TAoBR (°) | Trunk angle at the moment of BR |

TAoMIR (°) | Trunk angle at the moment of MIR |

PAoMKU (°) | Pelvic angle at the moment of MKU |

PAoFC (°) | Pelvic angle at the moment of FC |

PAoMER (°) | Pelvic angle at the moment of MER |

PAoBR (°) | Pelvic angle at the moment of BR |

PAoMIR (°) | Pelvic angle at the moment of MIR |

3. Parameters of trunk-pelvis separation (TPS) at time events | |

TPSoMKU (°) | TPS at the moment of MKU |

TPSoFC (°) | TPS at the moment of FC |

TPSoMER (°) | TPS at the moment of MER |

TPSoBR (°) | TPS at the moment of BR |

TPSoMIR (°) | TPS at the moment of MIR |

4. Parameters associated with special time events & intervals | |

AC1r (%) | Time ratio of AC1 |

AC2r (%) | Time ratio of AC2 |

AC2r-AC1r (%) | Time ratio interval between AC1 and AC2 |

5. Parameters those are important in stride phase | |

StrideL/BH (%) | Percentage of stride length normalized with body height |

MKH/BH (%) | Percentage of maximal knee height normalized with body height |

SFCD (°) | Stride foot contact direction |

Parameter | Pattern1 | Pattern2 | 95% CI | p Value |
---|---|---|---|---|

1. Parameters of timing of events | ||||

BRt-FCt (s) | 0.15 ± 0.03 | 0.17 ± 0.04 | −0.05~0.01 | 0.103 |

MKUr (%) | −475 ± 80 | −387 ± 100 | −168~−8 | 0.032 * |

MERr (%) | 81 ± 5 | 82 ± 4 | −5~4 | 0.717 |

MIRr (%) | 273 ± 48 | 262 ± 37 | −31~53 | 0.589 |

2. Parameters of angle at time events | ||||

TAoMKU (°) | −107 ± 8 | −99 ± 7 | −15~−0.3 | 0.043 * |

TAoFC (°) | −93 ± 12 | −97 ± 8 | −6~14 | 0.404 |

TAoMER (°) | 4 ± 7 | 11 ± 6 | −13~−1 | 0.019 * |

TAoBR (°) | 15 ± 6 | 22 ± 3 | −12~−2 | 0.005 * |

TAoMIR (°) | 82 ± 13 | 95 ± 15 | −25~−0.1 | 0.048 * |

PAoMKU (°) | −128 ± 10 | −133 ± 14 | −6~16 | 0.331 |

PAoFC (°) | −62 ± 6 | −74 ± 2 | 7~17 | <0.001 * |

PAoMER (°) | 5 ± 7 | −3 ± 8 | 0.6~14 | 0.035 * |

PAoBR (°) | 12 ± 7 | 4 ± 8 | 0.4~15 | 0.038 * |

PAoMIR (°) | 38 ± 11 | 37 ± 12 | −9~12 | 0.813 |

3. Parameters of trunk−pelvis separation (TPS) at time events | ||||

TPSoMKU (°) | 21 ± 9 | 34 ± 13 | −22~−3 | 0.011 * |

TPSoFC (°) | −31 ± 8 | −24 ± 6 | −15~−0.5 | 0.037 * |

TPSoMER (°) | −1 ± 7 | 14 ± 9 | −22~−8 | <0.001 * |

TPSoBR (°) | 3 ± 6 | 18 ± 9 | −21~−9 | <0.001 * |

TPSoMIR (°) | 44 ± 6 | 58 ± 21 | −25~−3 | 0.017 * |

4. Parameters associated with special time events & intervals | ||||

AC1r (%) | −100 ± 29 | −62 ± 11 | −62~−14 | 0.004 * |

AC2r (%) | 88 ± 16 | 65 ± 24 | 6~40 | 0.010 * |

AC2r-AC1r (%) | 191 ± 27 | 127 ± 24 | 40~88 | <0.001 * |

5. Parameters those are important in stride phase | ||||

StrideL/BH (%) | 69 ± 4 | 70 ± 3 | −4~3 | 0.651 |

MKH/BH (%) | 65 ± 5 | 67 ± 6 | −7~3 | 0.438 |

SFCD (°) | −7 ± 7 | −10 ± 10 | −5~11 | 0.407 |

6. Resultant parameter | ||||

Ball Speed (km/h) | 125 ± 6 | 119 ± 8 | 4~9 | <0.001 * |

**Table 4.**Correlation coefficients and cut-off values from ROC of each parameter correlated with ball speed and their Cohen’s d effect sizes (sorted by absolute value of correlation coefficient in order of high to low).

Parameter | Correlation Coefficient * | Cut-Off Value from ROC | Cohen’s d |
---|---|---|---|

PAoFC (°) | 0.613 | −69.95 | 2.68 |

BRt-FCt (s) | −0.527 | 0.19 | −0.57 |

MKUr (%) | −0.454 | −401.69 | −0.97 |

TPSoFC (°) | −0.335 | −24.92 | −0.99 |

The New Method | p Value | ||||||
---|---|---|---|---|---|---|---|

Type1 | Type2 | Type3 | Type4 | ||||

Ball speed (km/hr) | 126.1 ^{a}±5.3 | 120.2 ^{b}±9.4 | 120.8 ^{b}±5.6 | 120.5 ^{b}±8.9 | <0.001 * | ||

Expert’s decision | Pattern1 | 58.9% (53/90) | 10% (9/90) | 12.2% (11/90) | 18.9% (17/90) | -- | |

Pattern2 | 8.3% (5/60) | 23.3% (14/60) | 31.7% (19/60) | 36.7% (22/60) | -- |

^{a,b}the same superscripts indicate that no statistically significant difference are between the indicated groups (p > 0.05); * p value < 0.05. Note: Analysis of variance (ANOVA) is used for analysis of ball speed, and the results are shown in term of mean ± standard deviation.

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**MDPI and ACS Style**

Lin, Y.-C.; Chou, P.P.-H.; Lin, H.-T.; Shih, C.-L.; Lu, C.-C.; Su, F.-C. A New Method for Evaluating Pelvic and Trunk Rotational Pitching Mechanics: From Qualitative to Quantitative Approaches. *Int. J. Environ. Res. Public Health* **2021**, *18*, 905.
https://doi.org/10.3390/ijerph18030905

**AMA Style**

Lin Y-C, Chou PP-H, Lin H-T, Shih C-L, Lu C-C, Su F-C. A New Method for Evaluating Pelvic and Trunk Rotational Pitching Mechanics: From Qualitative to Quantitative Approaches. *International Journal of Environmental Research and Public Health*. 2021; 18(3):905.
https://doi.org/10.3390/ijerph18030905

**Chicago/Turabian Style**

Lin, Yu-Chuan, Paul Pei-Hsi Chou, Hwai-Ting Lin, Chia-Lung Shih, Cheng-Chang Lu, and Fong-Chin Su. 2021. "A New Method for Evaluating Pelvic and Trunk Rotational Pitching Mechanics: From Qualitative to Quantitative Approaches" *International Journal of Environmental Research and Public Health* 18, no. 3: 905.
https://doi.org/10.3390/ijerph18030905