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Original Research

Acute Effects of Partial-Body Cryotherapy on Isometric Strength: Maximum Handgrip Strength Evaluation

De Nardi, Massimo1; Pizzigalli, Luisa2; Benis, Roberto3; Caffaro, Federica4; Micheletti Cremasco, Margherita4

Author Information
Journal of Strength and Conditioning Research: December 2017 - Volume 31 - Issue 12 - p 3497-3502
doi: 10.1519/JSC.0000000000001797
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Abstract

Introduction

Muscle contraction is defined by the changes in length of the muscle during contraction: it can be classified into isotonic or isometric. Isometric contraction occurs when the muscle tenses without changing its length. It is required in some sports (for example climbing and gymnastics) and in physical and handwork activities. Isometric contraction is typical of muscles found in the hands and forearms. Many daily functions and sporting events require high activity levels of the flexor muscles of the forearms and hands. The most common method of assessment of grip strength is the use of a handheld dynamometer. This measurement may provide over all body strength and muscle performance, individual nutritional status and well-being, by a simple and noninvasive evaluation (28). During gripping activities, the muscles of the flexor mechanism in the hand and forearm create grip strength, while the extensors of the forearm stabilize the wrist (31). It is known that temperature is a relevant determinant of muscle performance (19,22). Regarding the cold, it can induce, for example, increased tissue stiffness (27), decreased nerve conduction velocity, and decreased muscle contractility. These effects could reduce athletic performance (11). Isotonic and isometric strength respond differently because of a decrease in temperature (14,18,26). In fact, we know (30) that dynamic activities are more susceptible to the inhibitory effects of cold than isometric contractions. Thus, interestingly, some studies reported that a cold application is an effective way to increase isometric strength (5,18). The human body responds to cold applications with vasoconstriction to maintain the core temperature. After this first response, usually the opposite phenomenon occurs, that is vasodilation, which increases muscle blood flow with increased oxygen supply, therefore potentially improving muscle performance (10).

Cryotherapy is the application of cold agents: It is based on body temperature, diminution through, for instance, immersion into cold water, and application of ice packs or ice vests. Its use is widespread in sports medicine today and the application of cold has been found to decrease the inflammatory reaction, the pain threshold, swelling, edemas and to reduce the recovery time after both acute and chronic injuries (16,17,29). One of the latest methods in sports medicine and science is whole-body cryotherapy (WBC). Whole-body cryotherapy is based on stimulation with very cold air of the organism of minimally dressed subjects (usually from −110 up to −160° C), either in a specially designed chamber (WBC) or a cabin (partial-body cryotherapy, [PBC]), for a short period (generally from 150 to 180 seconds), aiming to cause vasoconstriction of the skin vessels (2). The substantial difference between these 2 kinds of cryostimulation treatments is that during a cryocabin session (PBC), the head is not exposed (Figure 1). Whole-body cryotherapy and PBC are repeatedly used in sports practice to hasten the recovery after high-intensity exercises and increase the range of motion (7,9,25). In the past, despite the increasing popularity of WBC and PBC in sports and exercise medicine, a few studies have investigated the effectiveness of these treatments on muscle-performance recovery after exercise in adults (1,7), but to the authors' best knowledge, no study has examined the acute effects of cold dry air exposure on the maximum isometric strength. The hypothesis of this study was therefore that a single PBC session would not significantly worsen the handgrip maximum isometric strength. Considering the small differences in physiological reactions between WBC and PBC short exposure (15), the aim of this study was to test the hypothesis that a single PBC session could influence the maximum handgrip strength as measured by a hydraulic hand dynamometer. There are many categories of handheld dynamometer, and according to the literature (31), the handgrip dynamometer is a method of assessment which can provide the practitioner the most accurate choice, in addition to being an inexpensive tool and easy to use on the field.

Figure 1.
Figure 1.:
Subject during a cryocabin (Space Cabin, Criomed Ltd, Kherson, Ukraine) session.

Methods

Experimental Approach to the Problem

There are limited data about the effects of the cryogenic temperatures on isometric strength. Consequently, to evaluate the effects of a single PBC session performed before a maximum handgrip strength test, 100 healthy men and 100 healthy women were required to be present for one time at the testing venue. Both men and women populations were divided into experimental and control groups to assess the differences in maximum isometric strength after 150 seconds of standing rotations performed in a cryocabin or in a thermo neutral room. The study was a 2 (Control or PBC) × 2 (T0 and T1) design. This allowed us to determine the impact of the PBC on handgrip maximum isometric strength.

Subjects

All volunteers were adults and underwent an initial physical examination by the qualified physician; all participants with epicondylitis, chronic shoulder pain, episodes of fractured wrist, and disabilities in their upper extremities, and contradictions to PBC were excluded from the study. Subjects were all recreational athletes and were not accustomed to partial body treatments. To minimize the effects of circadian variation, the timing of measurements were consistent between trials. Subjects were also instructed to refrain from consuming alcohol, caffeine, theine, or hot drinks 24 hours before testing commenced to avoid influencing the recorded variable. In addition, participants were required not to undertake exercise for 24 hours before the laboratory trial. They were also instructed not to take medications or supplements during the study. One hundred men and 100 women were enrolled in the study, approved by the National Medical Ethics Committee, and signed a written informed consent. The research was undertaken in compliance with the Helsinki Declaration. Subjects were then randomly divided into a PBC and a control group (50 men aged 26 to 54 years and 50 women aged 26 to 53 in each group). Sociodemographic information for each group is shown in Table 1.

Table 1.
Table 1.:
Sociodemographic information of the participants (mean ± SD).*

Procedures

On arrival, the participants were made to sit for 30 minutes wearing only swimwear, socks, and wooden clogs to acclimate to the room temperature (22.0 ± 0.5° C). After acclimation, each participant performed the maximal handgrip strength test of the dominant hand (17) using a portable JAMAR Hydraulic Hand dynamometer (Sammons Preston Rolyan Nottinghamshire, United Kingdom) as recommended for use in healthy people (3,4). It was regulated for each subject: fitting the hand and allowing flexion at the metacarpophalangeal joints. When the individual adjustment operations were completed, each subject performed 3 submaximal voluntary isometric contractions maintained for 5 seconds as familiarization to the testing protocol. The scale of the dynamometer indicated handgrip strength in kilograms (kg).

Our experiment was conducted in May and June. The testing protocol consisted of 3 maximal voluntary isometric contractions maintained for 5 seconds with rest period of at least 60 seconds; the highest value was used for the determination of the maximal grip strength. The procedure and the methodology used during the handgrip strength test were performed according to the standards (20,21,24). Specific verbal instructions were given to subjects before the evaluations and the experiments were performed with verbal encouragement (23).

The PBC group, after the baseline handgrip strength measurement (T0 PBC), completed one treatment in a cryocabin (Space Cabin; Criomed Ltd., Kherson, Ukraine), an open tank equipped with a mobile lift which allows to adjust the height of every subject, so the guest is exposed to the very cold dry air up to the shoulders, with the neck and the head out of the cabin. This device can accommodate only one subject for each session (Figure 1). The 150 seconds duration and set temperature range between −130 and −160° C were used as recommended for cryocabin sessions (13). During the session, subjects wore swimwear, a pair of gloves, woolen socks, and wooden clogs. Participants were instructed to turn around continuously (standing rotations) in the cabin for the 150-second session. The control group, after the baseline measurement (T0 Control), was instructed to perform the same movements (standing rotations) for the same duration (150 seconds) in the turned off cryocabin (22.0 ± 0.5° C). After the cryocabin treatment (T1 PBC) or control duty (T1 Control), the maximal handgrip strength test was repeated.

Statistical Analyses

The SPSS for windows (SPSS 22.0, Inc., Chicago, IL) was used for statistical analyses. Data are presented as mean ± SD.

A series of independent t-tests was used to evaluate any possible differences in the anthropometric characteristics and differences among handgrip strength values both in female and male PBC and control groups.

A mixed-design repeated measures analysis of variance (ANOVA) was used to analyze handgrip strength values. Time (T0, T1) was the within-subjects factor, whereas group (PBC and control) and sex were the between-subjects factors. For all analyses, statistical significance was set at α = 0.05.

Partial eta-square (η2) effect sizes were determined and interpreted using the following criteria: 0.01 = small; 0.06 = medium; and 0.13 = large.

Results

Age, weight, height, and body mass index were not significantly different between PBC and control groups at baseline (p > 0.05) both in male and in female groups. Descriptive statistics regarding the handgrip strength values in all groups of participants are shown in Table 2. Whereas control group increased handgrip strength (mean values) from T0 to T1 around 0.5 kg in both genders, PBC group showed an increase of around 1.5 kg in men (Figure 2) and around 2 kg in women (Figure 3).

Table 2.
Table 2.:
Descriptive statistics of handgrip strength values (kg) at T0 and T1 in each group of participants.*
Figure 2.
Figure 2.:
T test partial-body cryotherapy (PBC) male group before cryotherapy (PBC T0) versus PBC male group after cryotherapy session (PBC T1) p < 0.007.
Figure 3.
Figure 3.:
T test partial-body cryotherapy (PBC) female group before cryotherapy (PBC T0) versus PBC female group after cryotherapy session (PBC T1) p < 0.0001.

A high intraclass correlation emerged (ICC 0.987), (95% confidence interval 0.975–0.992). The results of the ANOVA showed a significant main effect of exercise (continuously standing rotations) in both groups (F1.196 = 45.59, p ≤ 0.05, η2 = 0.189) on handgrip strength increase and a significant Exercise × Group interaction (F1.196 = 12.77, p ≤ 0.05, η2 = 0.061). Both PBC and control groups showed an increase in handgrip strength values compared with T0 (T0 = 39.55 kg, T1 = 40.68 kg), especially in the experimental group (Control: T0 = 39.48 kg, T1 = 40.01 kg; PBC: T0 = 39.61 kg, T1 = 41.34 kg) (Figures 4–5). The analysis also reported a significant effect of Gender (F1.196 = 491.99, p ≤ 0.05, η2 = 0.715), with female participants showing lower handgrip strength values compared with male participants (females = 30.43 kg, males = 52.27 kg).

Figure 4.
Figure 4.:
T test partial-body cryotherapy (PBC) female and male groups before cryotherapy (Control T0) versus PBC female and male groups after cryotherapy session (Control T1) p < 0.007.
Figure 5.
Figure 5.:
T test partial-body cryotherapy (PBC) female and male groups before cryotherapy (PBC T0) versus PBC female and male groups after cryotherapy session (PBC T1) p < 0.0001.

Discussion

The aim of this study was to test the hypothesis that a single PBC session would not significantly worsen the handgrip maximum isometric strength as measured by a hydraulic hand dynamometer in a large population of healthy men and women. We found an increase, compared with baseline, in the maximum handgrip strength after a short time period (150 seconds) both in the control group and in PBC group. Our results confirmed that immediately after a PBC session, there was a more remarkable increase in handgrip strength compared with baseline and to the control group. Although further investigation is warranted, from a practical perspective, the use of PBC may be important for individuals who practice activities where isometric strength is required (e.g., climbing and racket sports).

The results reported in this study are in line with others that evaluated the effect of cold agents on the maximal isometric force (5,18,30). In fact, a 10-minute cold bath provided an increase of the maximum isometric force production of the hip extensor significantly greater than that of the control and hot bath (water at 43° C) groups (5). Furthermore, Burke et al. found a gender difference in the cold group, with men experiencing greater increases. Additionally, a previous study verified that after placing ice on the arm for 15 minutes, muscle force increased significantly and, in line with our findings, even in the control group, there was a minimal increase in strength compared with baseline (18). Also, Vieira et al. (30) reported that 20 minutes of ice-pack application increased isometric peak torque of plantar flexors (p < 0.001) in healthy men.

The muscle temperature immediately after a PBC session is not known, but it is known (13) that skin temperature of the forearm is near to 23° C. Only one study, to the authors' best knowledge, evaluated the muscle temperature after a WBC session: Costello et al. (8) measured vastus lateralis temperature and recorded significantly lower temperatures (p ≤ 0.05) only after 20, 30, 40, 50, and 60 minutes after WBC. No significant differences (p > 0.05) were found immediately and 10 minutes after the cryogenic exposure. Therefore, it has been documented that a reduction on muscle temperature below the threshold of 27° C could decrease the maximal isometric force level (6). Hence, it would make sense, according to Westerlund (32), to assume that a single cold dry air exposure in PBC does not lead to reach the threshold of 27° C for the muscle temperature immediately after the session, under which a decrease of the maximal isometric force level occurs. To confirm this, immediately after a PBC exposure we noticed an increase in the maximal hand grip strength, that may be induced by the vasodilation occurred after the PBC session, which determines an increased blood flow to muscles and, according to Nodehi Moghadami and Dehghane (18), this may have a beneficial effect on muscle function. At the same time, other authors (12,30) suggested that the increase in isometric strength after cold exposures could depend on a compensatory mechanism that fosters the recruitment of higher threshold motor units in response to the inhibition caused by cooling, considering that this mechanism is prominent in isometric contractions because of lower dependence on this activity in relation to tissue stiffness caused by cooling.

Practical Applications

The results of this study provide the first evidence that a single session of PBC can have a significant and positive impact on isometric strength in healthy people. This is of practical value for coaches and practitioners aiming to include this treatment to improve isometric strength. Again, our results represent a new approach to the longstanding problem of the PBC protocols standardization. In fact, in light of what has emerged, it is now clear that coaches can schedule PBC sessions also before a training session or a competition, for example, climbing, racket sports, and gymnastics ring performances, where hand isometric strength is required.

Acknowledgments

The authors thank all participants involved in this study. No external financial support received. The results of this study were not endorsed by the National Strength and Conditioning Association.

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Keywords:

cryocabin; hand dynamometer; muscle performance; cryostimulation

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