📚 Experiment Design: The Force Applied by Muscles – Investigating Grip Strength and Fatigue | 实验设计：肌肉施加的力——握力与疲劳探究
Understanding how muscles generate and sustain force is fundamental in sport science and human biology. This article outlines a complete experimental design to measure the maximum voluntary grip force produced by hand muscles and to investigate how this force declines with repeated contractions, a phenomenon known as muscle fatigue. The procedure is suitable for a school or college laboratory and develops key skills in hypothesis formulation, variable control, data collection, and analysis.
理解肌肉如何产生并维持力量是运动科学和人体生物学的基础。本文提供一个完整的实验设计方案，用于测量手部肌肉产生的最大自主握力，并探究该力量在反复收缩时如何下降——这一现象称为肌肉疲劳。该步骤适用于中学或大学实验室，能培养假设提出、变量控制、数据收集和分析等核心技能。
1. Background: Muscle Contraction and Force Generation | 背景：肌肉收缩与力的产生
Skeletal muscles produce force through the sliding filament mechanism, where myosin cross-bridges pull on actin filaments. The total force a muscle can exert depends on the number of motor units recruited and the frequency of nerve impulses. During repeated maximal contractions, metabolic by-products such as lactic acid lower the pH, interfering with calcium release and cross-bridge cycling, which leads to a temporary decline in force output — muscle fatigue.
骨骼肌通过肌丝滑行机制产生力量，在此过程中肌球蛋白横桥拉动肌动蛋白丝。肌肉能够施加的总力量取决于被募集的运动单位数量和神经冲动的频率。在重复最大收缩时，乳酸等代谢产物降低pH，干扰钙离子释放和横桥循环，导致力量输出暂时下降——即肌肉疲劳。
The hand grip provides an accessible model for studying muscle force because the muscles of the forearm act on the fingers via long tendons, and a hand dynamometer can directly measure the isometric force generated. This experiment mimics real-world scenarios such as sustained gripping in rock climbing or repetitive manual work.
握力为研究肌肉力量提供了一个可操作的模型，因为前臂肌肉通过长肌腱作用于手指，而手握力计可以直接测量产生的等长力量。本实验模拟了现实中的情景，例如攀岩中的持续抓握或重复性手工劳动。
2. Aim and Research Question | 目的与研究问题
The aim of this experiment is to determine the maximum grip force generated by the dominant hand and to examine how this force changes over ten repeated maximal contractions. The research question is: “How does repeated maximal handgrip contraction affect the peak force exerted by the forearm muscles?”
本实验旨在测定优势手产生的最大握力，并考察该力量在十次重复最大收缩中如何变化。研究问题是：“重复的最大手握力收缩如何影响前臂肌肉所产生的峰值力？”
3. Hypothesis | 假设
It is hypothesised that the maximum grip force will decrease progressively across the ten trials. The null hypothesis states that there will be no significant change in peak force. The alternative hypothesis predicts a negative correlation between trial number and grip strength due to accumulating muscle fatigue.
假设十次测试中的最大握力会逐步下降。零假设认为峰值力无显著变化。备择假设则预测，由于肌肉疲劳的累积，试验次数与握力之间存在负相关关系。
4. Variables | 变量
Independent variable: Trial number (1 to 10), representing the number of repeated maximal contractions performed by the participant.
自变量：试验次数（1至10），代表参与者完成的反复最大收缩次数。
Dependent variable: Peak grip force, measured in newtons (N) using a calibrated hand dynamometer.
因变量：峰值握力，以牛顿(N)为单位，使用校准的手握力计测量。
Controlled variables:
控制变量：
- Same hand used for every trial (dominant hand) – avoids variation in muscle strength between hands.
- 每项试验使用同一只手（优势手）– 避免两手间肌力差异。
- Identical sitting posture – forearm resting on a table with the elbow at 90° – ensures consistent leverage.
- 相同的坐姿 – 前臂置于桌上，肘部呈90° – 确保杠杆作用一致。
- Grip span of the dynamometer adjusted to the same setting for all trials, matching hand size.
- 所有试验中握力计的握距调至相同设定，与手大小匹配。
- Rest interval between trials fixed at 30 seconds – controls recovery time.
- 试验间休息时间固定为30秒 – 控制恢复时间。
- Ambient temperature maintained at 20–22 °C – prevents temperature-related changes in muscle performance.
- 环境温度保持在20–22 °C – 防止温度对肌肉表现的影响。
5. Apparatus and Materials | 仪器与材料
- Calibrated hand dynamometer (digital or analogue, range 0–1000 N, resolution 1 N) – 校准手握力计（数字或模拟，量程0–1000 N，分辨率1 N）
- Adjustable chair and table – 可调座椅与桌子
- Goniometer or protractor to set elbow angle – 量角器或测角器以设定肘关节角度
- Stopwatch – 秒表
- Data recording sheet or spreadsheet – 数据记录表或电子表格
- Disinfectant wipes – 消毒湿巾
6. Detailed Method | 详细方法
The participant sits upright on a chair with their dominant hand placed on the table, elbow flexed at exactly 90°. The hand dynamometer is adjusted to fit the participant’s palm size and is held with the dial facing away. The participant is instructed to squeeze the dynamometer as hard as possible for 3 seconds, exhaling gently to avoid the Valsalva manoeuvre. The peak force reading is recorded in newtons. A 30-second rest period follows before the next contraction. This cycle is repeated for a total of 10 trials. The same procedure is carried out by at least three different participants to obtain class data and check for reproducibility.
参与者端正坐于椅子上，优势手放在桌上，肘部精确弯曲至90°。手握力计根据参与者的手掌大小调整，握持时表盘朝外。指导参与者尽全力握紧握力计持续3秒，同时轻柔呼气体以避免瓦尔萨尔瓦动作。记录峰值力读数（牛顿）。随后休息30秒再进行下一次收缩。此循环共重复10次。至少由三位不同参与者执行相同步骤，以获得全班数据并检查可重复性。
Between participants the dynamometer handle is cleaned with disinfectant wipes. Care is taken to ensure the participant does not look at the readings during the test to avoid any psychological influence on performance.
参与者之间用消毒湿巾清洁握力计手柄。注意确保参与者在测试中不看读数，以避免心理因素对表现的影响。
7. Risk Assessment | 风险评估
| Hazard / 危险 | Risk / 风险 | Control measure / 控制措施 |
|---|---|---|
| Overexertion causing muscle strain | Low – if participant has no pre-existing injury | Warm-up hand exercises; stop immediately if pain occurs |
| 过度用力导致肌肉拉伤 | 低 – 若参与者无旧伤 | 手部热身；若出现疼痛立即停止 |
| Hygiene risk from shared equipment | Low | Disinfect dynamometer after each participant |
| 共用设备卫生风险 | 低 | 每位参与者使用后消毒握力计 |
8. Expected Results and Data Recording | 预期结果与数据记录
It is expected that the grip force will be highest in the first or second trial and will then gradually decline. A sample data table for one participant is shown below. Students should record the peak force to the nearest newton and calculate class mean values for each trial to smooth individual variation.
预期握力在第一次或第二次试验中最高，随后逐渐下降。下方展示了一位参与者的示例数据表。学生应记录最接近的牛顿峰值力值，并计算每项试验的全班平均值，以平滑个体差异。
| Trial / 试验 | Grip Force (N) / 握力(N) |
|---|---|
| 1 | 385 |
| 2 | 390 |
| 3 | 372 |
| 4 | 360 |
| 5 | 348 |
| 6 | 335 |
| 7 | 322 |
| 8 | 310 |
| 9 | 298 |
| 10 | 285 |
A line graph of grip force against trial number should be plotted, with error bars representing the standard deviation of class data, to visualise the fatigue trend.
应绘制握力随试验次数变化的线图，误差线代表全班数据的标准差，以便直观显示疲劳趋势。
9. Data Analysis | 数据分析
To quantify the extent of fatigue, the fatigue index can be calculated using the formula below, where F₀ is the maximum force recorded (usually in the first trial) and Fₙ is the force in the final trial.
为了量化疲劳程度，可以使用下式计算疲劳指数，其中F₀为记录到的最大力（通常在首次试验），Fₙ为最后一次试验的力。
Fatigue Index (%) = (F₀ − Fₙ) ÷ F₀ × 100
A higher fatigue index indicates a greater percentage drop in force. If the index is above 20%, the muscles are considered to have experienced substantial fatigue under the given conditions.
疲劳指数越高，表示力量下降的百分比越大。若指数超过20%，则认为肌肉在给定条件下出现了显著的疲劳。
Statistical analysis, such as a paired t-test comparing the first and last trial means across all participants, can be used to determine whether the decline is statistically significant at the p < 0.05 level.
可采用统计分析，例如配对t检验比较所有参与者首次与末次试验的平均值，以确定该下降在p < 0.05水平上是否具有统计显著性。
10. Evaluation of the Experiment | 实验评估
Limitations:
局限性：
- Motivation and psychological factors can affect maximal effort; a subject may not always exert true maximum force.
- 动机和心理因素可能影响最大用力；受试者并非总能发挥真正的最大力量。
- The 30-second rest may not be sufficient for full recovery, especially for untrained individuals, which exaggerates fatigue.
- 30秒休息可能不足以完全恢复，尤其是对未经训练者，这会夸大疲劳程度。
- Small sample size reduces reliability; individual differences in muscle composition and fitness level influence results.
- 样本量小会降低信度；个体在肌肉组成与体能水平上的差异会影响结果。
- The analogue dynamometer might have parallax error when reading the dial.
- 模拟式握力计在读取表盘时可能存在视差误差。
Strengths: The method is simple, non-invasive, and uses readily available equipment. All key variables are controlled, and the quantitative data allow for graphical and statistical analysis.
优点：方法简单、无创，使用随手可得的设备。所有关键变量均得到控制，定量数据可以进行图分析和统计分析。
11. Improvements and Extensions | 改进与拓展
To improve validity, use a digital dynamometer with automatic peak-hold function to eliminate reading errors. Increase the sample size and include both genders, different age groups, and trained vs untrained individuals to explore the effect of athletic conditioning. A control experiment could measure grip strength without any rest interval between trials to see a more rapid fatigue curve. Repeating the whole procedure on the non-dominant hand would allow comparison of fatigue resistance between limbs.
为提高效度，可使用具有自动峰值保持功能的数字握力计，消除读取误差。增加样本量并纳入不同性别、年龄组以及训练与未训练个体，以探索运动训练的影响。可设置对照实验，测量无休息间隔下的握力变化，以得到更陡峭的疲劳曲线。在非优势手上重复整个过程，则可比较双侧肢体的抗疲劳能力。
The investigation could be extended by measuring the time taken for force to recover to 90% of the initial value after the final trial, giving insight into recovery kinetics. Combining the data with EMG recordings would link electrical activity with mechanical output.
该研究可扩展为测量末次试验后力量恢复到初始值90%所需的时间，从而了解恢复动力学。若将数据与肌电图记录结合，还可将电活动与力学输出关联起来。
12. Conclusion | 结论
This experiment provides a reliable and safe method to investigate the force applied by muscles and the phenomenon of fatigue. By collecting quantitative data under controlled conditions, learners can confirm that repeated maximal contractions reduce the grip force generated by forearm muscles. The degree of fatigue can be expressed through the fatigue index, and the design can be refined to yield more robust, generalisable findings. Such investigations deepen our understanding of muscle physiology and the principles of experimental design in biology.
本实验提供了一种可靠、安全的方法，用于探究肌肉施加的力量及疲劳现象。通过在受控条件下收集定量数据，学习者可以证实反复最大收缩会降低前臂肌肉产生的握力。疲劳程度可用疲劳指数加以表达，该设计还可进一步完善，以得出更可靠、可推广的结论。此类探究加深了我们对肌肉生理学以及生物学实验设计原理的理解。
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