Introduction
Maximal strength and power are influenced by many factors including muscle cross-sectional area and neural activation (13,19). Neural adaptations to resistance training improve the excitability of motor neurons and optimize muscle fibers recruitment and motor unit synchronization (5). Hypertrophy can involve all fiber typologies, leading the muscle to a significant increase in muscle size (21) and changes in muscle morphology (1). Muscle fibers recruitment and changes in cross-sectional area and muscle architecture influence both maximal strength and power expression.
In addition, psychological arousal appears to be particularly important for optimizing muscle activation. Explosive athletic performances, when a maximal neural activation is sustained for a limited time, and strength endurance are influenced by mental factors (14). Psychological arousal and mental preparation have been demonstrated to influence power and maximal strength performance (14). Furthermore, significant improvements in strength endurance have been reported when self-selected music was used to obtain optimal arousal in trained individuals (4).
The use of pre-workout supplements in an attempt to optimize both physiological and psychological performance is common among strength/power athletes and sport enthusiasts (7). In particular, caffeine, widely considered as a mild stimulant (3), represents a common ingredient of many pre-workout supplements (8). It is reported that many athletes competing in powerlifting and weightlifting use ammonia inhalants (AI) before or during the competition (16). Ammonia salts are often inhaled immediately before competition to increase the athlete's focus and aid in “psyching-up” (12). This practice is not banned by the World Anti-Doping Agency, but athletes participating in powerlifting contests are forbidden to use ammonia inhalants in front of the public (23).
Physiological reactions associated with the inhalation of aromatic spirits of ammonia include immediate irritation of the lungs and nasal cavity and activation of a rapid inhalation reflex (12). The incidence of reported adverse effects or complications with use of AI is limited (10). Significant increases in blood flow velocity in cerebral vasculature and heart rate have been reported following ammonia inhalation (15). Ammonia-dependent vasodilation constitutes a cardiovascular response and may provide a stimulatory effect (15). Some authors have suggested that ammonia inhalants may complicate the evaluation of injury during competitions by masking signs and symptoms of injury; thus, they discourage the use of AI during sport contests (22).
Despite the popularity of the use of AI, only a few scientific studies have investigated the effect of ammonia salt inhalation on maximal strength and explosive strength performance. Richmond et al. (17) reported no significant improvements in the number of repetitions performed to failure during a submaximal load (85% of 1 repetition maximum: 1RM) in both the bench press and back squat exercises. Similarly, Perry et al. (15) reported no ergogenic effects with the use of ammonia inhalants on strength expressed during an isometric midthigh pull (IMTP). To the best of our knowledge, no scientific studies have investigated the effects of AI on muscular power. Considering the lack of research relating to AI use and strength and power performance, the purpose of this study was to investigate the influence of ammonia inhalants on lower body power, and maximal force production, and the rate of force development during an IMTP. The hypothesis was that the use of AI might influence the rate of force development more than maximal strength expression in trained individuals.
Methods
Experimental Approach to the Problem
This investigation employed a counterbalanced crossover design consisting of 3 different assessment sessions performed in a randomized order selected by drawing lots. The participants reported to the laboratory on 3 separate occasions, 48 hours apart. During each assessment session, participants were asked to perform maximal strength and power tests using either an AI, a placebo (PL), or no inhalant (N). The experimental study was double-blinded and the substance inhaled before each trial (AI or PL) was unknown to the investigator or the participant.
Ammonia inhalant or PL was inhaled 10-seconds before each attempt for 3 seconds. Ammonia salts (Dynarex Corporation, Orangeburg, NY, USA) were provided in a 0.3-ml capsule that was crushed before the test and placed into a microcentrifuge tube. Placebo (Vicks VapoRub, Cincinnati, OH, USA) was in liquid form and was poured into a microcentrifuge tube. Following the suggestions provided by the product producer, a distance of 10 cm was maintained between the tube and the participant's upper airways in both AI and PL conditions.
Subjects
Twenty experienced resistance trained men (mean +/− SD age = 26.7 ± 3.7 years; body weight = 80.59 ± 9.0 kg; body height = 179.5 ± 5.7 cm; body fat = 9.12 ± 4.13%) volunteered to participate in this investigation. Participants were participating in a strength focused resistance training program a minimum of 3 days per week for more than 3 years (mean = 6.6 ± 3.5 years of experience); hence, they were familiar with powerlifting and weightlifting exercises. Following an explanation of all procedures, risks, and benefits, each participant provided his written informed consent to participate in the study. This investigation was approved by the institutional board of the University of Bologna. Exclusion criteria included injuries that occurred in the year before the study. Participants were asked to abstain from alcohol, caffeine, and resistance training for at least 24 hours before the tests.
Strength and Power Testing
Anthropometric evaluations were performed before the first assessment session. Body measurements included body mass, height, and body fat composition. Body mass was measured to the nearest 0.1 kg. Body fat percentage was estimated from skinfold caliper measures using the method of Evans et al. (6). The same investigators, with intraclass coefficients between 0.98 and 0.99, performed all of the skinfold analysis assessments. Before the strength and power assessments, participants performed a standardized warm-up consisting of 5 minutes on a cycle ergometer against a light resistance, 10 body weight squats, 10 body weight walking lunges, 10 dynamic walking hamstring stretches, 10 dynamic walking quadriceps stretches, and 2 squat jumps.
Peak power (CMJP) was calculated by the jump height and the participant's body mass using the following equation (1): Peak Power = 60.7 × jump height + 45.3 × body mass−2,055 (18). Participants performed 3 jumps with a 3-minute rest between each jump. They were required to keep their hands on their hips and were asked to maximize their jump height. The intraclass coefficient calculated for the CMJP was 0.96 (SEM = 100.3 W). Isometric maximal strength assessment consisted of an isometric midthigh pull (IMTP) on a power rack that permitted fixation of the bar at a height that corresponded to the participant's midthigh, while standing on a force plate (Kisler Force Plate, Winterthur, Switzerland, 500 Hz). Participants were instructed to assume a body position similar to the second pull of the snatch and clean. Knee angle, hip angle, and grip width were measured to reproduce the same position for all testing sessions (40° and 55° angles for knees and hips, respectively). Participants were secured to the bar using lifting straps and subsequently performed 3 maximal isometric pulls lasting for 6 seconds with a recovery time of 3 minutes between attempts.
For the IMTP, peak force was measured and rates of force development were calculated as previously described by Haff et al. (9). Peak rate of force development (pRFD20) was calculated using a 20 ms window. Intraclass coefficients were 0.94 (SEM = 158.4 N) and 0.72 (SEM = 1,102.5 N·s−1) for IMTP and pRFD20, respectively. During the isometric measurements, participants were strongly encouraged by the researchers.
Statistical Analyses
A Shapiro–Wilk test was used to test the normal distribution of the data. Data were analyzed using a 1-way repeated measures analysis of variance (ANOVA) to evaluate differences between conditions (AI, PL, and N). In the event of a significant F ratio, Bonferroni post hoc tests were used to determine pairwise differences. Pearson product–moment correlations were used to examine selected bivariate relationships. For effect size (ES), the partial eta-squared statistic was reported and according to Stevens (20), 0.01, 0.06, and 0.14 represents small, medium, and large effect sizes, respectively. All data are reported as mean ± SD. A significance level of p ≤ 0.05 was used.
Results
Results of the CMJ and IMTP are reported in Table 1. Results of the pRFD20 are depicted in Figure 1. A significant effect between trials was detected on pRFD20 (F = 6.68; p < 0.01; η2 = 0.323). Pairwise comparisons revealed significant differences between AI and N (p = 0.032) and between AI and PL (p = 0.009). No significant differences were detected between N and PL for pRFD20 (p > 0.1). No significant effects of time were found on IMTP (F = 3.85; p = 0.075; η2 = 0.157) and on CMJ (F = 1.44; p = 0.251; η2 = 0.087). A significant correlation was observed between force output during the IMTP and CMJ (0.62; p = 0.010). A significant correlation was also observed between the CMJ and the pRFD20 (0.495; p = 0.043).
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Table 1.: Power expressed in counter movement jump (CMJP) and maximal isometric force measured at isometric midthigh pull (IMTP) in normal condition (N), using ammonia inhalants (AI) or a placebo (PL).*
Figure 1.: Changes in peak rate of force development (pRFD20) expressed at isometric midthigh pull (IMTP) in normal condition (N), using ammonia inhalants (AI) or a placebo (PL). *Indicates a significant difference (p < 0.01) between the trials. All data are reported as mean and error bars represent SD.
No adverse effects of AI were reported by any participant in the present study.
Discussion
The inhalation of ammonia (AI) showed a significant effect on pRFD20 expressed during a maximal isometric midthigh pull test (IMTP). Greater rates of force production may be associated with the effects of AI on the psychological arousal during the isometric assessment. Results differ from those reported by Perry et al. (15), who reported no significant effects of AI on rate of force development expressed during an IMTP. These differences may be associated in part with the resistance training experience of the subjects. Participants in the latter study were healthy males experienced in resistance training but without a specific experience in weightlifting exercises. The high intersubject variability reported by the authors, likely related to the lack of competitive experience or in maximal effort in these exercises, may have contributed to large degree of variability between the treatments. In contrast, participants in the present study were experienced in weightlifting and powerlifting exercises. Interestingly, Perry et al. did report robust cerebrovascular and cardiovascular responses 15-seconds after inhalation of ammonia and demonstrated a stimulatory effect of these substances. Physiological responses to AI may be associated with the higher degrees of consciousness and alertness anecdotally reported by many athletes (12). The “psyching-up” effect (17) of AI may increase the rate of force development by stimulating the sympathetic branch of the autonomic nervous system and increase the psychic activation.
Consistent with Perry et al. (15), we found no significant effects of AI on maximal force during the IMTP. The pRFD20 appeared to be more sensitive to the psychological potentiation of AI compared with the maximal force expressed at IMTP. Maximal strength expression may be less dependent on the timing of muscle fiber recruitment than the RFD. In addition, no significant effects of AI on lower-body power were detected. The performance in CMJ is influenced by many technical components including the duration of the eccentric action and the maximal angle of knee flexion (11). These variables, in participants without a specific experience in vertical jumps, may have influenced the performance more than the use of AI.
Significant correlations between CMJ and IMTP confirm the importance of maximal strength for vertical jump performance. Interestingly, pRFD20 was significantly related to CMJ, but not correlated with maximal force expressed at IMTP. In conclusion, to the best of our knowledge, this is the first investigation to report significant ergogenic effects of AI on rate of force development measured during isometric contractions. Specifically, AI appeared to be able to enhance the rate of force development rather than maximal strength or jump performance. The neural mechanisms of strength, including muscle fiber recruitment, may be more sensitive to the stimulation of AI, likely related to the AI effects on central nervous system function.
Practical Applications
Ammonia inhalants are widely used in maximal strength and power sports such as weightlifting and powerlifting. Results of the present study confirm the ergogenic potential of these inhalants to enhance strength performances when used immediately before the lift. In particular, the positive effect of AI on the rate of force development may represent an advantage in sports like weightlifting that requires high rates of force production. The use of AI during powerlifting may not be as effective because high rates of force production are not required and the performance is mainly related to maximal strength production (2).
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