Biomechanical analysis of an explosive movement in seniors: a comparative study applied to vertical jumping
The execution of so-called "explosive" movements shows a particularly marked decline throughout aging. Although discreet in daily life, decrease in power qualities is one of the first markers of the collapse of functional capacities of an aging person. It conditions many daily activities and is fundamental to the prevention of falls. For this reason, we have chosen to study the alterations induced by aging in movements that require substantial power, among a population of senior males.
The objective of this work was to identify the mechanical contribution of the muscles crossing the joints of the lower limbs and to understand the neuromuscular adjustments resulting from these numerous changes. To address this issue, we chose to study the execution of vertical jumps (squat jumps) performed at maximum intensity comparing populations of older (74.5 years old ± 4.6 years) and younger men (21.6 years old ± 6.22 years). A dynamic and kinematic analysis of squat jumps was carried out to characterize the modifications of this standardized multi-joint explosive movement in seniors.
Our findings show a decrease in jumping performance in the elderly, resulting from a decrease in joint power. The latter is marked as much by the alteration of strength as by that of speed. Our observations also reveal a significant decrease in the mechanical work of the ankle, knee and hip joints in seniors. Contrary to the results observed while walking or running, this population does not counterbalance the alteration of the distal joints efforts by increasing the work of the more proximal joints efforts. This decrease in mechanical work for each of the joints is mainly due to a decrease in joint endeavor during jumping, while joint amplitudes remain unchanged. From a mobility point of view, our results confirm that a proximo-distal coordination pattern is used during the squat jump among both young and senior athletes. However, it differs in the elderly by earlier knee joint extension as compared to the younger group. The inter-articular coordination strategy of the seniors also shows greater variability during jump execution. This demonstrates an adaptation of the neuromuscular system to compensate for strength deficiencies in seniors and to guarantee their balance and stability.
These principle results confirm the need to strengthen all the muscles crossing the joints of the lower limbs, in order to maintain or even improve explosive movements. In addition, preventive training including strength reinforcement should be carried out for the elderly, at high speeds, as strength and speed are complementary. They also illustrate the importance of including dynamic movement exercises in training or rehabilitation program designs, in particular jumps to boost central nervous system plasticity, thereby enabling more complex tasks and optimizing inter-articular coordination. Hence jumps have their role to play among power rehabilitation exercices, and, to a larger extent, in the preservation of explosive movements and autonomy in the elderly.
