Enhancing Grip Strength Through Grip Training with Strengtheners

Abstract

Grip is an essential hand movement to human function and health. The stronger one’s grip strength (GS), the more stable their grip, and the better they can perform tasks with their hands. Society is in need of a simple and effective hand exercise to strengthen individuals’ GS. One potential solution is grip training with strengtheners. This study investigated the effectiveness of grip training, with resistance from grip strengtheners, in helping improve GS. 24 participants (14 males and 10 females) formed the experimental group (EG) and continuously attended grip training for ten days. Before and after their training, their cylindrical grip strength (CGS) and pinch strengths (PS, including three subtypes) were measured with a hand dynamometer and a pinchmeter, respectively. The differences between final and initial measurements were calculated and compared with corresponding values from the control group (CG), who did not attend training. Except in the lateral pinch strength (LPS), EG generally exhibited greater improvements in GS than CG, supporting the alternative hypothesis. Although, on average, the additive effects of grip training are statistically insignificant (p>1.714, ɑ = 0.05, df = 23), more EG cases exhibited statistically significant GS improvements than CG cases, which reflected the effectiveness of grip training. These limited improvements can be attributed to neural adaptation rather than hypertrophy: training raised motor unit recruitment and firing rates, intensifying excitatory signals sent to the muscles. Thus, muscles contract to a greater extent during grips, resulting in improved GS. Further analysis can be conducted to compare GS improvements across dominant and non-dominant hands, biological sexes, and age groups. Based on the study’s limitations, future research should diversify training configurations to engage forearm and hand muscles fully. The duration of training should be extended to demonstrate the long-term impact on GS improvements.

Question

Compared to those who lack grip training, how do 10 continuous days of grip training on a grip strengthener (50 “hand squeezes”/hand/day) impact the grip strength of healthy, non-athletically competitive individuals?

Hypotheses

Alternative hypothesis [H1]:

If healthy, non-athletically competitive individuals perform 10 continuous days of grip training on a grip strengthener (50 “hand squeezes”/hand/day) while maintaining their regular routine, then they will exhibit more GS improvement than those who lack grip training.

Null hypothesis [H0]:

If healthy, non-athletically competitive individuals perform 10 continuous days of grip training on a grip strengthener (50 “hand squeezes”/hand/day) while maintaining their regular routine, then they will exhibit the same GS improvement as those who lack training.

Background Research

Figure 1. Types of power grips and precision/pinch grips (Types of Grip, 2023; Magee & Manske, 2020). “Cylinder” refers to cylindrical grip; “Chuck or three-fingered pinch” is the same as palmar pinch.

As one of the most physically active human organs, the hand mainly functions to grip objects with various configurations. Grips are classified into two major grip types: power grip and precision grip (Magee & Manske, 2020). Power grips, specifically the cylindrical grip, require more force than precision or pinch grips. Cylindrical grip strength (CGS) reflects one’s ability to hold onto objects and perform force-demanding manual tasks. Meanwhile, to accomplish a precision or pinch grip, the digits need not only strength but also fine coordination. Strong pinch strength (PS) allows one to manipulate small objects. Collectively, stronger grip strength (GS) is correlated to lower risks of developing various internal diseases and higher standards of living due to improved gripping performance (Glazier & Ko, 2023). Given the significance of GS to human health and function, my study investigated the effectiveness of grip training, with resistance from grip strengtheners, in helping improve GS.

It has been widely proven that resistance training can build muscle strength through neural adaptation and hypertrophy (Fritzsch et al., 2020). Accordingly, grip training with resistance can build strength in hands and forearms, ultimately improving human health. Although a 2017 grip training study supported this point, it targeted professional rock climbers whose GS, and possibly the rate of neuromuscular development, were well above normative levels even before training (Levernier & Laffaye, 2019). The intensive and professional training program in this study is also unsuitable for non-athletically competitive individuals. Other studies investigate the effectiveness of grip training in rehabilitating patients, but none is tailored for non-athletically competitive individuals with healthy hands, the majority in society (Shang et al., 2021).

My study addressed this gap in GS research by designing a training program for healthy, non-athletically competitive individuals, ultimately advocating for an intuitive and effective exercise to improve hand function. Because healthy, non-athletically competitive individuals determine the baseline of health for the general population, my study has a wide implication for society. It advances the long search for an effective hand exercise to recover or improve GS. Implementing such exercises in hand rehabilitation programs can facilitate functional improvement in people who experience grip weakness, such as stroke and Parkinson’s disease patients, ultimately improving their living standards and well-being.

Materials

General setting requirement: an indoor space with a flat floor and a chair. When seated, the participant’s feet must fully rest on the ground.

Figure 2. Handeful grip dynamometer for SGST.

Figure 3. Baseline pinchmeter for PST (pinch gauge).

Figure 4. Longang grip strengthener.

• 1 Handeful grip dynamometer for SGST (Figure 2)
• 1 Baseline 12-0475 Electronic Pinch Gauge (pinchmeter) for PST (Figure 3)
• 24 Longang grip strengtheners with adjustable resistance for training (Figure 4)
• 1 chair for participants to sit on during the tests or training

Testing Methods

1. Standard Grip Strength Test (SGST)

Figure 5. Position and pose during SGST (Fess & Moran, 1981).

Figure 6. Second handle position on the Handeful hand dynamometer (Shock et al., 2019).

Orthopedic Physical Assessment stipulations:

• Sit upright and frontally;
• Arm should be adducted to one’s sides and neutrally rotated, and elbow should rotate to 90°; i.e., the thumb is at the top and the pinkie is at the bottom;

• Feet should naturally rest on the ground;
• Hold the dynamometer in the second handle position;
• Grip three times, and take the mean CGS (kg) from the three measurements;
• Grip with maximum strength. Release the grip after perceiving maximum strength;
• Position and pose should minimally change during the test;
• There can be supporting objects or hands under the dynamometer (Fess & Moran, 1981).

2. Pinch Strength Test (PST)

Figure 7. The three pinch types in a PST: (A) tip pinch (TP), (B) palmar pinch (PP, only the thumb and the radial digits are involved), (C) lateral pinch (LP). Abbreviations for corresponding pinch strengths are: TPS, PPS, and LPS Kong et al., 2014).

Fundamentals of Hand Therapy stipulations:

• Sit in the same position as SGST;
• Participant should not have long nails that impact pinching;
• Pinch three times for each pinch type, and take the mean strength (kg) from the three measurements;
• The pinching force should primarily originate from the hand, not the forearm (Cooper, 2006).

3. Grip Training

Figure 8. The “hand squeeze” configuration for grip training (Longang Store, n.d.)

Stipulations:

• Squeeze with maximum strength;
• Complete 50 squeezes for each hand per day.

Time requirement:

Daily training sessions should be approximately 24 hours apart (intervals within 22-26 hours are all acceptable). There are no time constraints per training session; one can take a 1-minute break for every 10 grips.

Procedures

The experiment consisted of two GS testing sessions over a 10-day interval, in which EG conducted grip training. Each session included two separate tests: the Standard Grip Strength Test (SGST) and the Pinch Strength Test (PST). For both tests, the study followed standard procedures stipulated by the American Society of Hand Therapists and the book Fundamentals of Hand Therapy (Fess & Moran, 1981; Cooper, 2006). In SGST, the Handeful grip dynamometer will measure the participant’s CGS in kilograms (Figures 2, 5, and 6). Because pinch configurations vary significantly in form and function, the PST involved three distinct sub-tests for the Baseline pinchmeter to measure PS (Figures 3 and 7).

Both EG and CG consisted of 24 participants, including 14 males and 10 females. For EG, “hand squeeze” training with the Longang grip strengthener began on the same day as the initial testing session (Figure 4). Because the “hand squeeze” motion resembles a cylindrical grip, the grip strengthener was adjusted to the lowest resistance level above the participant’s minimum initial CGS (Figure 8). The training was designed to be progressive: the resistance level should increment when the participant could perform “hand squeezes” solely and consistently with their explosive power. Because no EG participant had met this criterion, they remained on the original resistance level throughout training. No participant quit the experiment midway.

Although the final testing session was scheduled 1 day (the 11th day) after the final day of training, it was advanced to 3 hours after the training (the 10th day) for 2 EG participants and 1 CG participant, postponed to the 12th day EG participants and 2 CG participants, and postponed to the 14th day for 2 EG participants. EG participants did not complete training during the 1-3 day hiatus. Another 2 EG participants missed 2 days of training. These deviations from the experimental design may have impacted the evaluation of GS improvements.

Results

Table 1. Mean change in the four types of GS.

Table 2. The number of participants with statistically significant GS improvements, assessed with 95% confidence intervals (unit: participant).

Figure 9. Comparison of improvements in dominant hand TPS between EG and CG.

Figure 10. Comparison of improvements in dominant hand LPS between EG and CG.

Except in LPS, EG had greater GS improvement than CG, supporting the alternative hypothesis (Table 1). However, statistical analysis using a one-tailed T-test resulted in all p-values exceeding the critical value (p>1.714, ɑ = 0.05, df = 23). Therefore, data for all grip types fail to reject the null hypothesis, suggesting that the 10-day grip training program’s additive effects on GS were not statistically significant.

Despite this finding, case analysis revealed that EG exhibited statistically significant GS improvements more frequently than CG, suggesting the effectiveness of grip training. For every grip type on each hand, 5-14 EG participants exhibit statistically significant improvement in their respective strengths because the 95% confidence intervals of the final and initial measurements do not overlap (Table 2). Except in LPS for the non-dominant hand, this number is consistently higher than that of CG. Therefore, the training program had overall facilitated GS improvements in EG.

Limitations in training, measurement, and calculation were noted. For instance, 3 EG participants each exhibited a disproportionately significant improvement in certain GS types (Figure 8). As outliers in the group, their measurements were potentially inaccurate. Furthermore, EG lacks one final dominant hand PS value, while CG lacks one final non-dominant hand CGS value, both due to hand injury outside of training. Missing values may have impacted the collective statistical significance of data. Still, the limitations did not affect the general pattern that EG exhibited more GS improvements than CG, which could be explained by biological mechanisms.

Discussion

Figure 11. A motor unit consists of a neuron and all the muscle fibers it innervates (Lesson Explainer: Muscle Contraction, n.d.).

Figure 12. Strength gains within short training periods (<8-12 weeks) can be attributed to neural adaptation (Pearcey et al., 2021).

Figure 13. The order of motor unit recruitment follows the “size” principle (Behind the Block: The 6-12 Method, 2020).

The relative GS improvements in EG were small, suggesting that neural adaptation, instead of hypertrophy, is the primary factor contributing to these gains (Fritzsch et al., 2020; Pearcey et al., 2021; Figure 12). Neural adaptation is the adaptation of the nervous system to the “hand squeeze” movement in the training program.

Previous studies have shown that short-term, repetitive resistance training—such as the 10-day grip training program in this study—intensifies neural activity and causes greater voluntary contraction in the prime mover muscles (Pearcey et al., 2021). This is either due to increased motor unit recruitment or a higher firing rate in already recruited neurons (Lundberg & McPhee, 2020). With resistance training, the threshold for activating motor neurons decreases, resulting in more motor units recruited. Meanwhile, synapses release more excitatory neurotransmitters in response to continuous neural activity, which increases excitatory input to the motor neurons while decreasing inhibitory input (Kim et al., 2019; Christie & Kamen, 2013). Therefore, the motor neurons’ firing rates increase. Under both mechanisms, the nervous system transmits more signals, in the form of action potentials, that stimulate contraction in the prime mover muscles, thereby improving muscle strength.

Motor unit recruitment follows the “size” principle: larger motor units are recruited after the smaller motor units (Sale, 1988; Figure 13). Accordingly, untrained individuals can recruit most motor units, which are located in the small intrinsic hand muscles, to control the pinches (TP, PP, LP). However, they can only exert 50% of the maximum voluntary contraction (Sale, 1988). Enhanced PS improvement in EG can thus be attributed to higher motor neuron firing rates. Because the larger motor units in the extrinsic forearm muscles are more difficult to recruit, enhanced CGS improvement in EG can be attributed to either increased motor unit recruitment or a higher firing rate.

The nature of “hand squeeze” movements may also have impacted the extent of improvement in each type of GS. A “hand squeeze” exercises the extrinsic forearm muscles since the digits must flex to close the grip strengthener, but it also involves the fingers’ opposition to the thumb, suggesting the use of intrinsic hand muscles. As a result, the training improved CGS, TPS, and PPS in EG. LPS did not improve likely because the “hand squeeze” movement does not target the thenar muscle group, which powers the pinch at the base of the thumb. The thumb remains relatively inactive in the “hand squeeze,” so grip training may not have significant effects on its strength.

Conclusion

Although after training, healthy, non-athletically competitive individuals exhibit more GS improvements than those who lack grip training, t-tests demonstrate that the improvements were not statistically significant. Thus, the results are inconclusive.

Future Direction of Research

Further research can compare GS improvements between 1) the dominant and non-dominant hands, 2) biological males and females, and 3) different age groups. I also acknowledge that my study may not fully represent the strengthener’s effectiveness in improving GS. To ensure a more comprehensive evaluation, the training can involve more types of hand configurations besides “hand squeeze” so that most, if not all, muscles in the forearm and the hand are exercised. An extended training period may yield more statistically significant data to explain the training’s effects, leading to more reliable conclusions; it also offers insights into the long-term impact of grip training on GS development.

See References here. See the poster version of my project here.