Modulation of Neural and Muscular Adaptation Processes During Resistance Training by Fish Protein Ingestions in Older Adults

Abstract

Assessments of both neural and muscular adaptations during interventions would provide valuable information for developing countermeasures to age-related muscle dysfunctions. We investigated the effect of fish protein ingestion on training-induced neural and muscular adaptations in older adults. Twenty older adults participated 8 weeks of isometric knee extension training intervention. The participants were divided into two groups who took fish protein (n = 10, Alaska pollack protein, APP) or casein (n = 10, CAS). Maximal muscle strength during knee extension, lower extremity muscle mass (body impedance method), and motor unit firing pattern of knee extensor muscle (high-density surface electromyography) were measured before, during, and after the intervention. Muscle strength were significantly increased in both CAS (124.7 ± 5.8%) and APP (117.1 ± 4.4%) after intervention (p < .05), but no significant differences between the groups were observed (p > .05). Significant increases in lower extremity muscle mass from 0 to 8 weeks were demonstrated only for APP (102.0 ± 3.2, p < .05). Greater changes in motor unit firing pattern following intervention were represented in CAS more than in APP. These results suggest that nutritional supplementations could modulate neural and muscular adaptations following resistance training and fish protein ingestion preferentially induces muscular adaptation without the detectable neural adaptation in older adults.

Fish Protein Ingestion Induces Neural, but Not Muscular Adaptations, Following Resistance Training in Young Adults

“…Since we noted no significant increases in muscle volume-related variables, the muscle strength gain in the present study may be primarily due to neural adaptations. In our previous study, increases in muscle volume following resistance training were observed in older adults with APP ingestion, but not in older adults with CAS ingestion (9). These present and previous findings suggest that the same training regimen with APP and CAS ingestion induces strength gains and muscular adaptations that differ in young and older adults.…”

“…Although we investigated the effect of APP ingestion on muscle strength, muscle volume, and motor unit activations in the present and previous study (9,22), detailed physiological mechanisms/pathways for the effect of fish protein ingestion on neuromuscular systems have not been clarified. Recently, the effects of fish-derived omega-3 fatty acids on muscle strength and volume has seen considerable interest (45, 46).…”

“…It is well-known that firing patterns are inconsistent among motor unit groups with different recruitment thresholds (30,31). Our previous studies demonstrated recruitment thresholddependent changes in motor unit firing patterns following resistance training (9,22). Also, since the relationship between motor unit firing rate and exerted force is not linear (21,32), firing rate should be analyzed at various force levels in order to assume the detailed neural adaptations.…”

“…The purpose of this study was to investigate the effect of fish protein ingestion on neural and muscular adaptation during resistance training intervention in young adults in order to clarify the age-specific neural and muscular adaptations in combinations of nutritional supplementation and resistance training. We hypothesized that the effect of fish protein ingestion on neural and muscular adaptations following resistance training would be different in young adults when compared with the results for older adults obtained in a previous study (9), because the contribution and/or sensitivity of neural and muscular adaptations to resistance training-induced muscle strength gain (3)(4)(5) and role of muscle protein synthesis with nutritional supplementation are markedly influenced by aging (16,17).…”

“…In fact, we previously reported a trade-off relationship between neural and muscular factors during intervention involving resistance training with protein supplementation. During 8 weeks of resistance training intervention, older adults who ingested fish protein showed gains in muscle strength with muscle hypertrophy but without marked motor unit adaptation, while older adults who ingested casein protein showed similar gains in muscle strength with marked motor unit adaptation but without muscle hypertrophy ( 9 ). Since previous studies already reported that fish protein intake induced greater muscle hypertrophy when compared with casein intake in rat muscle, enhancements of muscle hypertrophy following resistance training by the ingestion of fish protein in older adults may be likely to be reasonable ( 10 – 12 ).…”